JP4865291B2 - X-ray imaging device - Google Patents

Description

  The present invention relates to an X-ray imaging apparatus such as a digital X-ray imaging apparatus, a DR (Digital Radiography) apparatus, a cone beam CT apparatus, and an X-ray CT apparatus, and more particularly, a detector that acquires signals by switching a detection element for reading. The present invention relates to an X-ray imaging apparatus equipped with

  Here, an X-ray CT apparatus which is a kind of X-ray imaging apparatus will be described. The X-ray CT apparatus is an apparatus that can obtain a tomographic image of a subject, and is widely used in the fields of medical treatment and nondestructive inspection. In recent years, in order to realize a wider field of view, higher speed, and higher resolution of an image, miniaturization of detection elements, higher speed of scanning, and multi-row (multi-slice) detectors are progressing.

  However, the number of X-ray quanta incident per one X-ray detection element decreases as the area of the multi-slice X-ray detection element decreases. Become smaller. For this reason, the multi-slice CT is affected by noise, and the image quality is remarkably deteriorated due to circuit noise of the detector circuit and external noise generated by an external circuit.

  As a method for removing and reducing such extrinsic noise, some X-ray detection pixels of the X-ray detector are used as reference pixels, and the extrinsic noise of the X-ray detection element is estimated from the measured values. There is a correction method that uses it to remove and reduce extrinsic noise. In Japanese Patent Laid-Open No. 2000-33083, an X-ray detection element in which X-rays are not incident on a part of the X-ray detector is provided as a reference pixel, and using the data for correcting the line correlation noise measured by this reference pixel, A method for correcting the output data of the X-ray detection element has been proposed. One of the causes of line-correlated noise is exogenous noise, which can reduce the influence of exogenous noise. Japanese Patent Laid-Open No. 2002-158340 provides a reference pixel having a structure in which light from a scintillator does not enter a photoelectric conversion element in a part of an X-ray detector, and the output data of the reference pixel is used in the same manner. There has been proposed a method of correcting the output data of the X-ray detection element by this method.

JP 2000-33083 A JP 2002-158340 A

  However, in the above correction method, when applying the method of determining the extrinsic noise of the X-ray detection element using the reference pixel to the X-ray detector for switching the X-ray detection element for reading and reading the signal, There is a problem that the reference pixel is required. When this is performed by using a part of the X-ray detector, a large number of X-ray detection elements are required, so that the effective field of view of the X-ray detector is narrowed. Further, if the number of reference pixels is reduced, the reference pixel data cannot be acquired at the same time as the X-ray detector data acquisition, so that the accuracy of extrinsic noise correction is reduced.

  An object of the present invention is to remove and reduce the influence of extrinsic noise on an image in an X-ray imaging apparatus.

  In order to solve the above-described problems, an X-ray imaging apparatus according to the present invention includes an X-ray source that irradiates X-rays, and a plurality of X-ray detection elements that detect X-rays transmitted through a subject and convert them into electrical signals. And an X-ray detection means comprising an X-ray signal readout circuit for reading a detection signal from the X-ray detection element and converting it into a digital signal, a noise measuring element for generating an electric signal due to an extrinsic noise factor, and an extrinsic from the noise measuring element A noise measurement means comprising a noise readout circuit for reading out a noise signal and converting it into a digital signal; and an arithmetic means for calculating extrinsic noise contained in the digital signal of the X-ray detection means using the digital signal of the noise measurement means; Correction means for performing correction processing on the digital signal of the X-ray detection means using the calculation result of the calculation means, and the X-ray detection means includes one or more X-ray detection elements by an X-ray signal readout circuit. A plurality of simultaneous X-ray detection means for simultaneously reading out detection signals, and switching the simultaneous X-ray detection means a plurality of times to acquire data for one X-ray image. The readout circuit has a configuration in which at least one simultaneous noise measuring means for simultaneously reading out an extrinsic noise signal from at least one noise measuring element is arranged, and the simultaneous noise measuring means simultaneously detects the external signal simultaneously with the detection signal read out by the simultaneous X-ray detection means. At the same time, at least one identical simultaneous noise measuring means simultaneously reads the detection signal of the simultaneous X-ray detection means at different times and acquires an extrinsic noise signal. Reading is performed from the noise reading circuit and output to the calculation means.

  In order to obtain one X-ray image by such an X-ray imaging apparatus, for example, a sequential switching readout system, an X-ray detector that switches signals over time and reads out signals is mounted. In the X-ray imaging device, an exogenous noise signal is acquired simultaneously with each readout of the X-ray detection means using a small number of noise measurement elements without providing a separate noise detection element for each signal readout of the X-ray detection element. This makes it possible to accurately estimate the extrinsic noise, and to perform accurate correction. Furthermore, the signal of the extrinsic noise can be acquired simultaneously with the signal reading of each X-ray detection element, the extrinsic noise can be estimated with uniform accuracy in the X-ray image, and the correction accuracy is position-dependent. The artifacts that accompany it can be removed and reduced. Furthermore, it is possible to suppress or eliminate a reduction in detection area that occurs when a part of the X-ray detector is used as a noise measurement means. Furthermore, the installation location of the noise measuring means can be selected with a high degree of freedom compared with a method in which a part of the X-ray detector is used as the noise measuring means. Furthermore, compared with the conventional method, the number of reference pixels can be reduced, and this is advantageous in price.

  When the estimation means is configured to estimate the extrinsic noise of the X-ray detection element from the digital signal of the simultaneous noise measurement means that has read out the extrinsic noise signal simultaneously with the X-ray detection signal read-out, the non-integral that varies with time This makes it possible to accurately estimate the extrinsic noise of the mold and to perform accurate correction. Furthermore, high-speed processing is possible by estimating the extrinsic noise from the simultaneously measured noise signal.

  The estimation means performs the estimation of the extrinsic noise of the X-ray detection element, the X-ray detection element and at least one noise measurement element that has read out the extrinsic noise signal simultaneously with the X-ray detection signal readout. If it is configured to use the correlation with the extrinsic noise factor, the extrinsic noise of each X-ray detection element can be accurately obtained from the signal of the noise measuring means. Furthermore, it is possible to correct the variation in response to the extrinsic noise for each X-ray detection element, and to reduce and eliminate artifacts caused by the variation in response.

  In addition, the estimation means reads the detection signal of the X-ray detection element simultaneously with the noise signal readout simultaneously with the digital signal of the simultaneous noise measurement means, and the digital signal of one or more simultaneous noise measurement means with the noise signal readout non-simultaneously. If the X-ray detector is configured to estimate the extrinsic noise using, it can estimate not only the non-integral extrinsic noise but also the integral extrinsic noise, and correct the extrinsic noise more accurately. . Alternatively, by estimating the extrinsic noise of one X-ray detection element using data of noise measuring means measured at a number of times, it becomes possible to estimate and correct the extrinsic noise with high accuracy. .

  The digital signal of the simultaneous noise measuring means in which the X-ray detection means periodically reads out the signal for the X-ray image for each frame a plurality of times, and the estimation means reads out the noise signal simultaneously with the detection signal reading of the X-ray detection element. And the extrinsic noise of the X-ray detector using the digital signal of one or more simultaneous noise measuring means that read the noise signal in a frame different from the detection signal readout of the X-ray detector. Then, even in an X-ray imaging apparatus such as an X-ray DR apparatus, an X-ray CT apparatus, and an X-ray DR apparatus that continuously acquire X-ray images, an extrinsic noise correction effect can be realized. Furthermore, since the noise measurement signal can be obtained in excess of one frame, the degree of freedom in selecting noise data that uses extrinsic noise for estimation can be increased. Furthermore, since the noise measurement signal can be obtained over one frame, high-precision correction can be realized using a large amount of data.

  A signal obtained by weighting and adding the plurality of digital signals of the simultaneous noise measuring means that read out the noise signal in a time zone including the detection signal reading time of the X-ray detection element that performs the extrinsic noise estimation; If the configuration is such that the extrinsic noise is estimated using the correlation coefficient between the noise measuring means and the X-ray detection element, the extrinsic noise can be corrected at higher speed and with higher accuracy.

  At that time, if the weighting weight is uniform for a digital signal of each simultaneous noise measuring means in a certain time zone and zero in other time zones, the correction can be performed at higher speed. become. Further, when correcting X-ray images acquired continuously, the weighting signal of the next frame can be calculated with a small amount of signal processing from the weighting signal of the X-ray image of the previous frame, and high-speed processing can be realized. In addition, by providing a change means that changes the length of the time zone, changing the time zone changes the frequency of the extrinsic noise contained in the noise measurement signal, enabling estimation of the extrinsic noise in various periods. . This makes it possible to selectively correct external noise that affects the image quality. Furthermore, it becomes possible to use the optimal time zone in each environment, and the processing amount can be optimized.

  Further, the estimation means converts the signal read between the detection signal reading time T1 of the X-ray detection element and the detection signal reading time T2 of the same X-ray detection element in the X-ray image of the next frame into a digital signal. Among these, the extrinsic noise of the X-ray detection means that read out the X-ray detection signal at time T2 is estimated using a series of signals that do not include the signal read out at time T1 but includes the signal read out at time T2. With this configuration, it is possible to obtain a noise measurement signal that reflects the influence of an integral type extrinsic noise factor generated in the X-ray detection element particularly during one frame, and this has a strong correlation with the X-ray detection element. , Exogenous correction can be performed with high accuracy.

  According to the present invention, it is possible to remove and reduce extrinsic noise that causes image quality degradation by correction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Hereinafter, an X-ray CT apparatus, which is a kind of X-ray imaging apparatus, will be mainly described as an example. However, the present invention can be applied to an X-ray imaging apparatus other than the X-ray CT apparatus.

Example 1
FIG. 1 is an explanatory view showing an example of an X-ray CT apparatus according to the present invention.

  As shown in FIG. 1, the X-ray CT apparatus of the present embodiment has, as a basic configuration, an X-ray tube 100 that irradiates X-rays, an X-ray detector 104 that detects X-rays and converts them into electrical signals, and extrinsic. The extrinsic noise detector 184 that detects noise and converts it into an electrical signal, the signal collecting means 118 that collects signals from the X-ray detector 104 and the extrinsic noise detector 184, and the data from the signal collecting means 118 are stored. Central processing means 105 for performing image processing, display means 106 for displaying the results of image processing, input means 119 for starting imaging, setting and inputting parameters, X-ray tube 100 and X-ray detector 104, and detection of extrinsic noise And a control means 117 for controlling the device 184 and the rotating body 101. Here, although eight X-ray detectors 104 are shown in FIG. 1, the number of X-ray detectors is eight for the sake of simplicity, and does not limit the present invention. In addition, although eight extrinsic noise detectors 184 are installed on the back surface of each X-ray detector 104, this number and installation position are examples of implementation, and the present invention is not limited to this. .

  The shooting procedure will be described with reference to FIG. When the start of imaging is input from the input unit 119, X-rays are emitted from the X-ray source 100 toward the subject 102 placed on the bed top plate 103. Part of this X-ray passes through the subject 102, is detected by the X-ray detection element of the X-ray detector 104, and outputs an electrical signal corresponding to the X-ray dose. This electrical signal is analog-digital converted (AD converted) by the signal collecting circuit 118 to become a digital signal. In this imaging, a collection of digital signals obtained from a plurality of X-ray detection elements (see FIG. 2) constituting the X-ray detector 104 constitutes one projection image. In synchronization with this X-ray signal readout, the signal is read out using the extrinsic noise detector 184. At this time, the extrinsic noise signal generated by the extrinsic noise factor is acquired. This signal is also subjected to analog-digital conversion (AD conversion) by the signal collection circuit 118 to become a digital signal.

  In tomographic imaging, the rotating body 101 on which the X-ray tube 100, the X-ray detector 104, and the extrinsic noise detector 184 are mounted is rotated in the rotation direction 108, thereby changing the X-ray irradiation angle on the subject. Thus, a projection image for 360 degrees is acquired for each projection. This acquisition is performed, for example, every 0.4 degrees. During this time, the control means 117 controls the rotation of the rotating body 101 and the reading of the X-ray detector 104 and the extrinsic noise detector 184. The central processing unit 105 performs image correction processing and reconstruction calculation on the acquired projection image. The result is displayed on the display means 106.

  An example of the X-ray detector 104 used in the X-ray CT apparatus of the present invention will be described with reference to FIG. The X-ray detector 104 is arranged in a plurality of arcs as shown in FIG. 1 so as to make X-rays enter from the direction 406 and is arranged to face the X-ray tube 100. 108 are arranged so as to correspond to the rotation axis direction 107 and the rotation direction 108 of FIG. The X-ray detector 104 includes a plurality of scintillator elements 112 that convert X-rays into light, a photodiode (not shown) that converts light into an electrical signal, and a switching element (not shown) that switches ON / OFF of signal readout. It has a wiring substrate 113 having a photoelectric conversion substrate 111, an electrode pad 120 for inputting and outputting signals, and wirings for guiding these signals. The scintillator element 112 and the photoelectric conversion substrate 111 are bonded with an optically transparent adhesive 310, and one scintillator element 112 divided by a separator 130, a pair of photodiodes, and a switching element constitute one X A line detection element is formed. Here, the number of X-ray detection elements of the X-ray detector 104 shown in FIG. 2 is eight in order to simplify the description, and does not limit the present invention.

  FIG. 3 is an example of a circuit diagram of the X-ray detector 104 of FIG. 2 viewed from the X-ray incident direction 406, and the circuit configuration of the X-ray detector 104 will be described using this. Here, i (= 1, 2) is the number in the channel direction of the X-ray detection element, j (= 1, 2, 3, 4) is the number in the slice direction, and the X-ray detection element 110 is 110-i-j. It will be expressed as Other components are also described in the same manner.

  The photodiode 140-i-j and the switching element 134-i-j shown in FIG. 3 are fabricated on the photoelectric conversion substrate 111 shown in FIG. Here, the photodiode 140-i-j in FIG. 3 has a capacitance. The capacitance may be a parasitic capacitance of the photodiode or may be provided separately. The scintillator element 112-i-j shown in FIG. 2 is adhered to the photodiode 140-i-j to constitute the X-ray detection element 110-i-j. One of the electrodes of the X-ray detection element 110-i-j on the same photoelectric conversion substrate 111 is electrically connected to the ground electrode pad 135 by a common ground line 141. The other electrode is connected to the drain electrode of the switching element 134-i-j. The source electrode of the switching element 134-i-j is a current-voltage converter that converts a current signal into a voltage signal through a common signal line 142-i for each photodiode 140-i-j located in the same channel i. Via 124, the signal pad 120-i is electrically connected. The gate electrode of the switching element 134-i-j is electrically connected to the control pad 133-j through the common control line 143-j for each photodiode 140-i-j located in the same slice j. ing. With this structure, when a control ON signal is input to the control pad 133-j, the signals of the X-ray detection elements 110-i-j located in the same slice j are simultaneously transmitted from the signal pad 120-i. Can be read. Further, when the control pad 133-j for inputting this control signal is sequentially switched to j = 1, 2, 3 and 4, the X-ray detection element 110-i belonging to the same channel i from the signal pad 120-i. -J electrical signals can be read sequentially.

  4 is a diagram showing an example of the arrangement of the X-ray detector and the extrinsic noise detector 184. As shown in FIG. Since the X-ray detector 104 and the extrinsic noise detector 184 generate noise even by visible light or the like, they are installed in the dark box 189. In the present embodiment, the extrinsic noise detector 184 is disposed on the back side of the X-ray detector 104 (the side opposite to the X-ray incident surface). However, this arrangement is an example of implementation, and the present invention is not limited to this. Between the X-ray detector 104 and the extrinsic noise detector 184, X-rays are prevented from entering a photoelectric conversion substrate 180 on which a photodiode (not shown in FIG. 4) is formed as an extrinsic noise detector. An X-ray shielding plate 183 is provided. As the X-ray shielding plate 183, a X-ray shielding plate 183 that does not easily transmit X-rays and that has little influence on external noise factors is used. This is in order not to lower the correlation between the extrinsic noise detector 184 and the X-ray detector 104 to the extrinsic noise factor, so that the positional distribution of the extrinsic noise factor is not affected. is there. For example, an X-ray generation system can be considered as a source of extrinsic noise, and its radioactive magnetic field is considered to be a major extrinsic noise factor, so it is better not to use a ferromagnetic material such as iron (such as iron) For example, a metal plate made of aluminum or aluminum alloy is used. By using the X-ray shielding plate 183, a detector similar to the X-ray detector 104 can be used as the noise detector 184. Furthermore, the noise detector can be arranged near the X-ray detector, and a signal having a strong correlation with the X-ray detector with respect to the extrinsic noise factor can be obtained by the noise detector. , High-precision correction can be realized.

  The X-ray detector 104 and the extrinsic noise detector 184 may differ in sensitivity to the extrinsic noise factor depending on the direction. For example, since the X-ray detector 104 and the extrinsic noise detector 184 of this embodiment have a wide cross-sectional area with respect to the X-ray incident direction 406 or the opposite direction, the X-ray detector 104 and the extrinsic noise detector 184 are easily affected by the direction. In order to accurately estimate the extrinsic noise of the X-ray detector 104, for example, the sensitivity of the exogenous noise detector 184 is set so that the extrinsic noise detector 184 has sensitivity in the same direction as the X-ray detector 104. It is desirable to arrange them so that they are within a range of 10% or more of the highest sensitivity, or within a range of ± 45 degrees in the direction of highest sensitivity.

  FIG. 5 is an example of a circuit diagram of the extrinsic noise detector 184 shown in FIG. The extrinsic noise detector 184 includes an exogenous noise detecting element 181 that includes a photodiode 190 that outputs an electric signal due to the influence of the extrinsic noise factor, and a switching element 191 that controls ON / OFF of the signal from the photodiode 190. And a wiring board 182 having wiring for reading out the signal. The wiring board 182 includes a control pad 188 that supplies a control signal to the switching element 191, a current-voltage converter 186 that converts a signal from the photodiode 190 into a voltage signal, an electrode pad 185 that outputs the signal, A ground electrode 187 electrically connected to the ground potential of the photodiode 190 is included. With such a structure, when the photodiode 190 accumulates the charge generated by the extrinsic noise factor and inputs a signal readout ON signal from the control pad 188 to the switching element 191, a voltage signal depending on the charge amount is generated. Obtained from electrode pad 185.

  An example of signal readout timings of the X-ray detector 104 and the extrinsic noise detector 184 will be described with reference to FIG. A signal 150-j (j = 1, 2, 3, 4) in FIG. 6 is a timing signal for reading a signal generated in the X-ray detection element belonging to the j-th row of the X-ray detector 104, and is shown in FIG. Each is input to the control pad 133-j (j = 1, 2, 3, 4). A signal 151 is a timing signal for reading a signal generated by the extrinsic noise factor in the extrinsic noise detector 184, and is input to the control pad 188 shown in FIG. These signals are at a high level (in FIG. 6, the signal level when the signal is stabilized after rising) (ON) when the signal is read (ON), and at a low level (in FIG. 6, the signal is stabilized after falling) Is the time when the signal is not read (OFF). Here, FIG. 6 illustrates the read timing of only two frames, but this number of frames is for the sake of simplicity and does not limit the present invention.

  In FIG. 6, time 152 is one frame time, and signals are read by sequentially switching the X-ray detection elements from the first slice (j = 1) to the fourth slice (j = 4) during one frame. The extrinsic noise detector 184 reads the signal of the extrinsic noise detector 184 simultaneously with the signal reading of the X-ray detection element 110 in all slices of j = 1, 2, 3 and 4. Here, the signal reading is to read out an electric signal generated in the X-ray detection element 110 by X-rays or an electric signal generated in the extrinsic noise detector 184 due to an extrinsic noise factor. In this embodiment, the charge generated in the photodiode 140 of the X-ray detection element 110 and the photodiode 190 of the extrinsic noise detector 184 is read out, and the switching element 134 (see FIG. 3), This is executed by turning ON 191 (see FIG. 5). The simultaneous signal readout of the X-ray detection element 110 and the extrinsic noise detector 184 means that there is a time that overlaps the time of signal readout. In this embodiment, the switching element 134 and the switching element 191 It means that there is an overlap in the time when is turned on. That is, the signal readout time 160 and the signal readout time 164 shown in FIG. 6 are the signal readout time 161 and the signal readout time 165, the signal readout time 162 and the signal readout time 166 are the signal readout time 210 and the signal readout time. 214, signal readout time 211 and signal readout time 215, signal readout time 212 and signal readout time 216, respectively, signal readout time 163 and signal readout time 167, signal readout time 213 and signal readout time. Since each of 217 has an overlap time 168 in signal readout, it is at the same time.

  In this way, for example, by controlling the extrinsic noise detector 184 at the timing shown in FIG. 6, using one extrinsic noise detector 184, all signals are read out simultaneously with the X-ray detector 104, respectively. Noise signal readout can be performed.

  An example of processing of the central processing unit 105 of the X-ray CT apparatus shown in FIG. 1 will be described with reference to FIG. This processing includes pre-processing for extracting and storing the characteristics of the X-ray detector 104 in advance, real-time processing for correcting a signal obtained during actual imaging using the stored detector characteristics, and There is. In FIG. 7, dotted arrows represent pre-processing, and solid arrows represent real-time processing.

  As indicated by the dotted arrows in FIG. 7, in the preprocessing, the detector characteristic extraction unit 407 extracts the characteristics of the detector and the system using the signals of the X-ray detector 104 collected in the signal collection unit 118. In this process, for example, a projection image is obtained by irradiating X-rays when an object is not previously arranged, and a process for obtaining the X-ray distribution and the sensitivity characteristics of the X-ray detector 104, or no X-ray irradiation in advance. Processing to obtain a zero level (offset level) of the X-ray detector 104 and its readout circuit. The acquired characteristic is stored in the detector characteristic storage means 303.

  As pre-processing for extrinsic noise correction, the correlation of the response to the extrinsic noise factor between the extrinsic noise detector 184 and the X-ray detection element 110 used for correction is determined and stored in the detector characteristic storage means 303. This is used when the extrinsic noise of the X-ray detection element 110 is calculated from the output value of the extrinsic noise detector 184. This correlation is obtained when, for example, imaging is performed by irradiating X-rays with an X-ray shield provided immediately in front of the X-ray detector so that X-rays do not enter the X-ray detection element 110. It can be obtained from the output of the X-ray detection element 110 and the output of the extrinsic noise detector 184. At this time, for example, the ratio (correlation coefficient) of noise generated between the X-ray detection element 110 and the extrinsic noise detector 184 is calculated for each X-ray detection element 110.

  As indicated by the solid line arrows in FIG. 7, in the real-time processing, the correction unit 301 uses the detector characteristics and system characteristics stored in the detector characteristic storage unit 303 to correct the projection image acquired by actual photographing. Make corrections. The processing performed at this time includes, for example, sensitivity correction processing for correcting an actual image using the X-ray distribution and sensitivity characteristics of the X-ray detector 104, and dark current of the X-ray detector 104 using offset level characteristics. This is an offset correction process that excludes the output of minutes. Here, the contents of real-time processing of extrinsic noise will be described below with reference to FIG.

  After the correction process is performed by the correction unit 301, a convolution (convolution) or back projection (back projection) process is performed by the reconstruction unit 302 to reconstruct a cross-sectional image of the X-ray absorption coefficient distribution of the subject. This cross-sectional image is displayed on the display means 106.

  An example of extrinsic noise correction processing performed by the correction processing unit 301 in FIG. 7 will be described with reference to FIG. The extrinsic noise correction of this embodiment is performed for one X-ray detector 104 using the signal of one extrinsic noise detector 184 arranged on the back surface thereof.

  The correction unit 301 first outputs the digital signal of the X-ray detector 104 for one slice output from the signal acquisition unit 118 to the X-ray detector signal storage unit 411 and simultaneously reads the digital signal of the extrinsic noise detector 184. The signals are stored in the extrinsic noise measurement value storage means 410, respectively. Next, the extrinsic noise for each X-ray detection element 110 is calculated using the data stored in the extrinsic noise measurement value storage means 410 and the correlation between the X-ray detection element 110 and the extrinsic noise detector 184 for correction. And the result is stored in the estimation result storage means 412. The correlation is obtained in advance as described above, and is stored in the extrinsic noise estimation means 408. Next, the correction processing means 409 subtracts the estimation result stored in the estimation result storage means 412 from the data stored in the X-ray detector signal storage means 411 to remove the extrinsic noise. The data corrected for extrinsic noise in this way is output to the reconstruction means 302. This process is performed for each slice, and is similarly performed for the subsequent frames.

  In this manner, the extrinsic noise included in the output of the X-ray detector 104 is corrected using the signal of the extrinsic noise detector 184 that has been read simultaneously with the X-ray detector 104. With the X-ray CT apparatus as described above, it is possible to remove the extrinsic noise of the X-ray detector 104, in particular, the non-integrating external noise.

  The readout method and circuit configuration used in this embodiment are an example of a method of sequentially reading out signals from the X-ray detector 104, and the present invention is not limited to this. In the present embodiment, reading is realized simultaneously in the channel direction and sequentially in the slice direction, but there may be a circuit configuration in which reading is simultaneously performed in the slice direction and sequentially in the channel direction. In this case, extrinsic noise correction can be realized by the structure and control in which the slice and the channel are replaced in the present embodiment. Further, there may be a reading method and a circuit configuration in which reading is performed by sequentially switching for each set of one or a plurality of X-ray detection elements 110. At this time, similarly to the present embodiment, it may be controlled to read the signal of the extrinsic noise detector 184 simultaneously with the signal reading of the set of the X-ray detection elements 110.

  In this embodiment, the signal reading time width of the X-ray detector 104 and the signal reading time width of the extrinsic noise estimation means 408 (for example, the width of time 160 and the time 164 in FIG. 6) are the same. However, the present invention is not limited to this. There may be cases where the signal readout time of the extrinsic noise estimation means 408 is shorter than the signal readout time of the X-ray detector 104 or vice versa.

  In this embodiment, an X-ray detector that converts light converted from X-rays into an electrical signal is used as the X-ray detector 104. However, this is an example of the embodiment, and the present invention is not limited to this. Absent. For example, an X-ray detector that directly converts X-rays into electrical signals may be used.

  In this embodiment, the extrinsic noise detector 184 is arranged for each X-ray detector 104 on the back surface of the X-ray detector 104 (opposite surface to the X-ray incident surface). It is not limited. The location of the extrinsic noise detector 184 includes the front surface of the X-ray detector 104 and the end position in the slice direction (direction 107 in FIG. 2) (upper and lower portions of the X-ray detector 104 shown in FIG. 2). In the case of being arranged on one or both of them, the end position of the X-ray detector 104 in the rotation direction 108 (see FIG. 1) (the end of the arc of the X-ray detector 104 arranged in the arc shown in FIG. 1) ) May be arranged. A number of extrinsic noise detectors 184 irrelevant to the number of X-ray detectors 104 may be used. Further, the signal of any extrinsic noise detector 184 may be used to correct the extrinsic noise of an X-ray detector 104. Further, extrinsic noise correction may be performed using signals calculated from a plurality of extrinsic noise detectors 184. For example, as in the present embodiment, signals obtained by simultaneous measurement of eight extrinsic noise detectors 184 are added and averaged, and this added average signal is applied to all X-ray detection elements 101 measured at the same time. It may be used to correct.

  In this embodiment, the case where a photodiode is used as the extrinsic noise detector 184 has been described. However, this is an example of the embodiment, and the present invention is not limited to this. In addition to photodiodes, various detectors that can detect an electric field, a magnetic field, an electromagnetic wave, heat, and acceleration to obtain an electrical signal can be used. In addition, various detections such as a detector that generates a signal according to the absolute amount of at least one of electric field, magnetic field, electromagnetic wave, heat, position, and velocity, and a detector that generates a signal according to the amount of change. Can be used. As a result, for example, it is possible to measure extrinsic noise caused by a change in heat and extrinsic noise caused by a change in acceleration caused by vibration or the like. It is also possible to use a detector that is converted into another physical quantity and then converted into an electrical signal. For example, a detector that converts light into heat and then converts it into an electrical signal can be used. A plurality of these detectors may be used. For example, an extrinsic noise detector that detects extrinsic noise caused by electromagnetic waves may be used in combination with an extrinsic noise detector that detects extrinsic noise caused by heat.

  In this embodiment, the correlation between the extrinsic noise detector 184 and the X-ray detection element 110 is approximated by a proportional expression, and the extrinsic factor of the X-ray detection element 110 is determined from the signal of the extrinsic noise detector 184 based on the correlation coefficient. However, the present invention is not limited to this. The correlation may be obtained by a polynomial function or various nonlinear functions. Further, the extrinsic noise of the X-ray detection element 110 may be estimated from the signal of the extrinsic noise detector 184 by any method regardless of the use of the function. The estimation may be performed using not only one extrinsic noise environment but also the result of changing the strength (amount) of the extrinsic noise factor by, for example, changing the X-ray tube current. Further, in this embodiment, the correlation with the extrinsic noise detector 184 is obtained for each X-ray detection element, but this is an example of the embodiment, and the present invention is not limited to this. The case may be the case of each of a plurality of X-ray detection elements 110 that perform reading simultaneously, or the case of each X-ray detector 104. Further, it may be the same for all X-ray detection elements. Further, when the correlation coefficient is 1 for all X-ray detection elements, that is, the measurement value obtained from the extrinsic noise detector 184 may be used as the extrinsic noise of the X-ray detection element 110.

  In this embodiment, as the extrinsic noise detector 184, a case is used in which the charge generated by the extrinsic noise is accumulated for sampling and the sampling time width, that is, a detector that integrates the electrical signal and generates an output signal. Although described, this is an example of implementation and the present invention is not limited to this. For example, a detector that does not accumulate a signal, such as a coil that generates a voltage due to a change in the magnetic field and does not have a capacitor that accumulates the signal, may be used.

  In the present embodiment, the X-ray shielding plate 183 is provided in front of the extrinsic noise detector 184, but this is an example of the embodiment, and the present invention is not limited to this. When X-rays are sufficiently shielded by the X-ray detector 104, the X-ray detector 104 may also function as the X-ray shielding plate 183, and it may not be necessary to separately provide the X-ray shielding plate 183. As another embodiment, there may be a structure in which a part of the X-ray detector 104 also functions as the X-ray shielding plate 183. In the case of a detector that does not generate a signal due to X-rays, the X-ray shielding plate 183 may not be provided, and the detector may be disposed in a space irradiated with X-rays, for example, the front surface of the X-ray detector.

  In this embodiment, the extrinsic noise correction processing is performed for each slice, but the present invention is not limited to this. For example, after acquiring data for one frame and storing it in the X-ray detector output storage means 411 and the extrinsic noise measurement value storage means 410, the extrinsic noise of each X-ray detection element 110 is estimated, and the result is obtained. It may be used to perform extrinsic noise correction. Further, extrinsic noise correction may be performed in combination with other correction processing. For example, the extrinsic noise correction and the offset correction may be performed simultaneously by adding the estimated value of the extrinsic noise to the zero level (offset level) data of the actual data and subtracting this from the actual data.

  In the present embodiment, the circuit diagram of FIG. 5 is shown as an example of the circuit configuration of the extrinsic noise detector 184, but the present invention is not limited to this. For example, there is a case where reading is performed discretely outside without providing the switching element 191 for each element. At this time, the signal reading from the electrode pad 185 may be performed as in the timing shown in FIG.

(Example 2)
In the first embodiment, the removal of non-integral extrinsic noise has been described. In the second embodiment, the integration-type exogenous noise removal will be described.

  FIG. 9 is a diagram for explaining an example of extrinsic noise correction processing performed in the correction processing unit 301 of the present embodiment. First, the digital signal of the extrinsic noise detector 184 output from the signal collecting means 118 is stored in the extrinsic noise measurement value storage means 410, and the digital signal of the X-ray detector 104 is stored in the X-ray detector signal. Store in means 411. At this time, except for the first frame, data for one frame (one projection image) is stored. Next, a weighting signal is created from a plurality of data stored in the extrinsic noise measurement value storage means 410. For example, the weighting signal for extrinsic noise correction at time 210 shown in FIG. 6 is the adding means 413 for the signal of the extrinsic noise detector 184 read at time 165, time 166, time 167, and time 214. Calculate by weighting and adding. This signal reflects the influence of the extrinsic noise factor accumulated from the previous reading by the X-ray detection element 110 in the first column, that is, the influence of the extrinsic noise factor for one frame, and the extrinsic factor generated during that time. Since the signal is obtained by integrating the noise, the integral type extrinsic noise of the X-ray detection element is strongly reflected. Next, the extrinsic noise is estimated for each X-ray detection element 110 using the correlation between the weighted signal and the X-ray detection element 110 to be corrected and the extrinsic noise detector 184. This correlation is obtained in advance and stored in the extrinsic noise estimation means 408. This estimation result is stored in the estimation result storage means 412.

  This weighting weight is, for example, uniform at a certain time and zero at other times. At this time, the weighted signal is an averaged signal of the digital signals of the extrinsic noise detector 184. Specifically, for example, the weighting signal P (210) used in the X-ray detection element 101 at the readout time 210 in FIG. 6 is the signal of the extrinsic noise detector 184 at the readout times 165, 166, 167, and 214 (each O (165), O (166), O (167), O (214)), P (161) = O (165) / 4 + O (166) / 4 + O (167) / 4 It can be calculated by the averaging process of + O (214) / 4. Further, the weighting signal P (211) used in the X-ray detection element 101 at the next readout time 211 is set to P (211) = P (210) −O (165) using the weighting signal P (210) at the previous time. / 4 + O (215) / 4 can be calculated. Thus, since the processing amount of the process of calculating the next weighting signal from the previous weighting signal does not depend on the number of slices, it is advantageous for a detector having a large number of slices, for example, a detector having four or more slices, High-speed processing can be realized.

  Next, the correction processing means 409 performs the extrinsic noise correction by subtracting the extrinsic noise stored in the estimation result storage means 412 from the data stored in the X-ray detector signal storage means 411. After this extrinsic noise, the data is output to the reconstruction means 302.

  Through the processing as described above, it is possible to remove and reduce the extrinsic noise of the X-ray detector 104, particularly the integral-type exogenous noise.

  The weight described in the present embodiment is an example, and the present invention is not limited to this. For example, there can be various weighting methods such as weighting depending on time and weighting in which the weight is changed according to the output of the extrinsic noise detector 184. There may also be a case where a threshold is provided and the weight is changed by comparison with the threshold.

  In the present embodiment, the case where the weighted signal is obtained from the signal of the extrinsic noise detector 184 for one frame has been described, but the present invention is not limited to this. For example, the weighted signal may be obtained by using a signal of several slices or a section longer than one frame. In this case, the frequency range of the extrinsic noise included in the weighted signal changes depending on the section in which the weighted addition is performed. For example, as the interval becomes shorter, the weighting signal includes even high-frequency extrinsic noise components. Therefore, it is possible to efficiently remove the integral-type extrinsic noise by calculating the weighting signal in a section where a component having a large influence on the projection image can be extracted. By optimizing this section, it is possible to reduce the amount of data. Furthermore, a function of changing this section may be provided. Thereby, for example, the effect of the extrinsic noise correction can be adjusted by changing this section while confirming the projected image. In addition, for example, by automatically adjusting this section so that the SNR of the projection image is maximized, it is possible to perform effective extrinsic noise even in an environment where the extrinsic noise factors are different.

  In the present embodiment, as the extrinsic noise detector 184, a detector that accumulates the charge generated by the extrinsic noise for the duration of sampling and sampling, that is, integrates the electric signal to generate an output signal is used. Although the case has been described, this is an example of implementation, and the present invention is not limited to this. For example, a detector that does not have a function of accumulating signals, such as a coil that generates a voltage by a change in a magnetic field, may be used. However, in the case of a detector that integrates an electric signal to generate an output signal, for example, the added value Padd of the signal of the extrinsic noise detector 184 sampled many times between T1 and T2 is only T1 and T2. However, when using a detector that does not have a function for accumulating signals, the signal Pad may have a difference between the signal and PT2.

  In the present embodiment, only the case of correcting the integral type extrinsic noise is described, but this is an example of the embodiment, and the present invention is not limited to this. By using both the method of the first embodiment for correcting non-integral extrinsic noise caused by voltage fluctuation during sampling, both the integral and non-integral extrinsic noise can be corrected. That is, for example, when estimating the extrinsic noise of the X-ray detection element 110 at time 211, the addition obtained by weighted addition to the signal of the extrinsic noise detector 184 acquired at times 166, 167, 214, and 215 The integration type extrinsic noise is estimated using the signal, and the non-integration type extrinsic noise is estimated using the signal of the extrinsic noise detector 184 acquired at time 215. At this time, for example, the correlation between the extrinsic noise detector 184 and the X-ray detection element 110 is used. This needs to be measured and determined in advance. In this determination, when the integral type correlation is determined, the addition signal and the signal of the X-ray detection element 110 are used, and in the non-integration type estimation, the extrinsic noise detector 184 obtained at the same time is used. The signal and the signal of the X-ray detection element 110 are used. Since this sum signal also includes non-integral extrinsic noise, the integral extrinsic noise is estimated and the non-integral extrinsic noise is Some will be included. In this case, a value obtained by weighting and adding the estimated values of the extrinsic noise of the integral type and the non-integral type may be used as the estimated value of the total extrinsic noise. The weighting value may be determined so that the influence of the extrinsic noise of the X-ray image is minimized, specifically, for example, the SNR of the X-ray image is minimized. However, the integration type and non-integration type extrinsic noise estimation methods described above are examples of the embodiments and do not limit the present invention.

(Example 3)
The X-ray CT apparatus according to the third embodiment of the present invention is different from the first or second embodiment in that the extrinsic noise is estimated using a fitting function.

  An example of the estimation method in the present embodiment will be described with reference to FIG. 10, the vertical axis 270 represents the output value of the extrinsic noise detector 184, and the horizontal axis 271 represents the elapsed time. The time at which signal readout ends at the readout times 164, 165, 166, 163, 167, 214, 215, 216, 213, and 217 in FIG. 6 is indicated by dotted lines as the acquisition time of each signal. The output value of the extrinsic noise detector 184 acquired at each time is indicated by a black circle, and the result of fitting to this is indicated by a curve 201. This fitting curve 201 can be described by a polynomial, for example.

  When the signal readout of the X-ray detection element 110 substantially coincides with the signal readout of the extrinsic noise detector 184, for example, when obtaining the extrinsic noise at time 214, the extrinsic factor acquired from time 165 to time 167, for example. The fitting curve 201 is estimated from the output value of the characteristic noise detector 184, and the extrinsic noise is estimated using the value at the time 210 of the curve 201. At this time, in order to correct the variation in the correlation between each X-ray detection element 110 and the extrinsic noise detector 184, the correlation may be used. Similarly, when obtaining the integral type exogenous noise at time 214, for example, a value obtained by integrating the curve 201 in the section from time 164 to time 214 is used.

  On the other hand, when the signal readout of the X-ray detection element 110 does not completely match the signal readout of the extrinsic noise detector 184, for example, when obtaining the extrinsic noise at time 213, for example, from time 214 to time 217 The fitting curve 201 is estimated from the output value of the extrinsic noise detector 184 acquired in the above step, and the extrinsic noise is estimated using the value at the time 213 of the function 201. Similarly, when obtaining the integral type extrinsic noise, for example, a value obtained by integrating the curve 201 in a section from time 214 to time 213 is used. In this way, even when the signal readout of the X-ray detection element 110 does not completely coincide with the signal readout of the extrinsic noise detector 184, the integral and non-integral extrinsic noise can be accurately estimated.

  Thus, by using the fitting curve, it is possible to estimate the extrinsic noise while suppressing the influence of signal fluctuation such as thermal noise in the extrinsic noise detector 184.

  In this embodiment, the signal of the extrinsic noise detector 184 for one frame is used for calculating the fitting curve. However, the present invention is not limited to this, and a signal having a section longer than one frame is used. Or, a signal of less than one frame may be used. In addition, although the case where the time for obtaining the extrinsic noise falls within the interval in which the data for determining the fitting curve is acquired has been shown, the present invention is not limited to this, and the extrinsic noise is reduced using the fitting curve. It may be obtained by extrapolation.

Example 4
The X-ray CT apparatus according to the fourth embodiment of the present invention uses an extrinsic noise detector 184 composed of a plurality of exogenous display elements. This embodiment will be described with reference to FIG. 11 showing an example of the extrinsic noise detector 184 and FIG. 12 showing an example of the extrinsic noise correction process.

  In the first embodiment shown in FIG. 5, the extrinsic noise detector 184 is composed of one extrinsic noise detecting element, whereas the exogenous noise detector 184 of the present embodiment is shown in FIG. Thus, it is comprised of three extrinsic noise detection elements 181 in the channel direction. Here, the reason why the number of the extrinsic noise detection elements 181 shown in FIG. 11 is three is to simplify the explanation, and does not limit the present invention. The extrinsic noise detection element 181 is composed of a photodiode 190 and a switching element 191, and is formed on the photoelectric conversion substrate 180. The extrinsic noise detecting element belonging to the i channel is denoted as 181-i. In addition, the photodiode 190, the switching element 191, the current-voltage converter 186, and the electrode pad 185 are similarly described.

  The switching element 191-i of the extrinsic noise detection element 181-i is electrically connected to the common control pad 188. When a read-on control signal is input to the control pad 188, the extrinsic noise detection of each channel is performed. Signals are simultaneously output from the element 181-i. The signal 151 shown in FIG. 6 is input to the control pad 188, for example, as in the first embodiment. The signal output at this time is output from the electrode 185-i via the current-voltage converter 186-i for each channel i.

  Next, an example of an embodiment of the extrinsic noise detection element output signal processing of this example will be described with reference to FIG. First, the correction processing means 301 stores the digital signal of the extrinsic noise detector 184 output from the signal collecting means 118 in the extrinsic noise measurement value storage means 410, and the digital signal of the X-ray detector 104 is stored in the X-ray. The data is stored in the detector signal storage means 411. Next, sensitivity / offset correction means 415 performs sensitivity / offset correction on the digital signal of the extrinsic noise detection element 181. This sensitivity correction is a correction that normalizes the sensitivity of each extrinsic noise detection element 181, and the offset correction is a correction that matches the zero level when no X-rays are incident. For these corrections, sensitivity correction data and offset correction data acquired in advance and stored in the detector characteristic storage means 303 are used. The sensitivity correction data can be created, for example, by calculating the sensitivity of each extrinsic noise detection element 181 from the extrinsic noise signal generated by operating the X-ray drive system. The offset correction data can be created by calculating the zero level of each extrinsic noise detection element 181 from the detector signal measured in a situation where the extrinsic noise factor is small enough to be ignored.

  Next, the averaging means 414 performs an averaging process on the signal from the extrinsic noise detection element 181-i. In this embodiment, for example, all signals for three channels are added and averaged. Since the extrinsic noise detection element 181-i (i = 1, 2, 3) is simultaneously measuring, one extrinsic noise detection element 181 is formed by three elements, and the calculated addition average signal is One exogenous noise detection element 181 in Example 1 can be regarded as a signal measured at a certain time. Therefore, the processing after the addition averaging means 414 is the same as that in the first embodiment, so that the extrinsic noise in the X-ray detector signal storage means 411 can be estimated and extrinsic noise correction can be performed.

  By using the signals of the plurality of extrinsic noise detection elements 181 in this way, the estimation accuracy of the extrinsic noise is improved. This is because the thermal noise of the extrinsic noise detection element 181 has no correlation in each element, so that it is close to zero by averaging, whereas the extrinsic noise is caused by the same factor. This is because there is a correlation, and the average of the addition reduces the measurement variation and approaches the true value, so that a signal with a better SNR can be obtained than when measuring with one element.

  In this embodiment, both the sensitivity correction and the offset correction of the extrinsic noise detection element 181 are performed. However, the present invention is not limited to this, and only one of the corrections or both may not be performed. obtain. In particular, when the sensitivity variation is small or the offset level can be regarded as almost zero, the respective correction processes may be omitted.

  In the present embodiment, a plurality of extrinsic noise detection elements 181 are arranged in the channel direction 108, but the present invention is not limited to this, and when a plurality of exogenous noise detection elements 181 are arranged in the slice direction, It may be arranged at an angle with respect to the direction.

  In this embodiment, the averaging is performed using the signals of the extrinsic noise detection element 181 arranged in one extrinsic noise detector 184, but the present invention is not limited to this, and a plurality of extrinsic noises are used. A signal from the extrinsic noise detection element 181 disposed in the detector 184 may be used.

(Example 5)
The X-ray CT apparatus according to the fourth embodiment uses the extrinsic noise detector 184 in which the extrinsic noise detection elements 181 are arranged one-dimensionally, whereas the X-ray CT apparatus according to the fifth embodiment uses the external noise. An extrinsic noise detector 184 in which detection elements 181 are two-dimensionally arranged is used. An example of the extrinsic noise detector 184 of this embodiment is shown in FIG. 13, and an example of the control timing of the exogenous noise detector 184 of FIG. 13 is shown in FIGS.

  As shown in FIG. 13, the extrinsic noise detector 184 of the present embodiment has a configuration in which the extrinsic noise detecting elements 181 are arranged two-dimensionally in 3 channels × 2 slices. Here, the number of channels and the number of slices of the extrinsic noise detection element 181 shown in FIG. 13 are merely examples, and do not limit the present invention. The extrinsic noise detection element 181 includes a photodiode 190 and a switching element 191, and is formed on the photoelectric conversion substrate 180. The extrinsic noise detecting element belonging to the i channel j slice is denoted as 181-i-j. In addition, the photodiode 190 and the switching element 191 are similarly described. Similarly, current-voltage converters belonging to the i-th channel are referred to as 186-i and electrode pads 185-i. Similarly, a control pad 188-j for controlling the jth slice is described.

  The extrinsic noise detector 184 reads out, for example, as shown in the control timing of FIG. This reading is realized by inputting the control signal 151-j (j = 1, 2) shown in FIG. 14 to the control pad 188-j (j = 1, 2) shown in FIG. The line detection element 110-i-j (j = 1, 2, 3, 4) sends a control signal 150-j (j = 1, 2, 3, 4) to the control pad 133-j (j = 1, 2, 3 and 4), respectively, to control. With this control, the extrinsic noise signals of all the extrinsic noise detecting elements 181 are read out simultaneously with the X-ray detecting element 110. The signals read simultaneously at this time are added and averaged in the adding process 414 shown in FIG. When being controlled and processed in this way, as in the fourth embodiment, the extrinsic noise detecting element 181 of 3 channels × 2 slices is regarded as one extrinsic noise detecting element 181 and used for extrinsic noise correction. I can do it. As described above, by increasing the number of extrinsic noise detection elements 181 used for the averaging, the SNR of the signal is improved and the estimation accuracy of the extrinsic noise is improved.

  However, the control method of the extrinsic noise detector 184 is not limited to this. For example, the control may be performed as shown in FIG. Control signals 151-j (j = 1, 2) shown in FIG. 15 are respectively input to control pads 188-j (j = 1, 2) shown in FIG. At this time, the extrinsic noise detection element 181-i-1 in the first slice reads out signals simultaneously with the X-ray detection elements 110-i-j in the first and second slices, and the extrinsic noise detection element 181 in the second slice. -I-2 performs signal readout simultaneously with the 3 and 4 slice X-ray detection elements 101-i-j. The signals acquired at the same time are added and averaged in the addition process 414 shown in FIG. 12, so that the extrinsic noise detecting element 181 of 3 channels × 1 slice is regarded as one extrinsic noise detecting element 181 and extrinsic noise is detected. It can be used for correction. By dividing the extrinsic noise detector 184 in this way, the extrinsic noise detecting element 181 located close to the X-ray detecting element 110 to be corrected for extrinsic noise or the extrinsic noise detecting element 181 having a strong correlation can be obtained. As a result, the signal can be corrected, so that a highly correlated signal can be acquired from the extrinsic noise detector 184.

(Example 6)
In the X-ray CT apparatus of Example 1 or Example 2, the signal readout of the extrinsic noise detection element 181 and the signal readout of the X-ray detection element 110 were in the same period, whereas the X-ray CT apparatus of Example 6 The signal reading of the extrinsic noise detection element 181 is also performed during the signal reading of the X-ray detection element 110.

  An example of the control timing of the extrinsic noise detector 184 of this embodiment will be described with reference to FIG. Reading of the extrinsic noise detector 184 is controlled by inputting the control signal 151 shown in FIG. 14 to the control pad 188 shown in FIG. Reading of the X-ray detection element 110-i-j (j = 1, 2, 3, 4) is performed by using the control signal 150-j (j = 1, 2, 3, 4) as the control pad 133-j in FIG. (J = 1, 2, 3, 4) is controlled by inputting it respectively. The extrinsic noise detector 184 performs signal readout at times 244, 245, 246, and 247 in addition to acquiring simultaneously with the signal readout times 160, 161, 162, and 163 of the X-ray detection element 110. Here, in this embodiment, during the signal readout of the X-ray detection element 110, the case where the extrinsic noise detection element 181 reads a signal only once non-simultaneously is shown, but this number is for simplifying the explanation. It is not intended to limit the invention.

  In this embodiment, in order to estimate non-integral extrinsic noise, the signal of the extrinsic noise detecting element 181 read simultaneously with the signal reading time of the X-ray detecting element 110 and the signal read non-simultaneously are added. And use. For example, for estimation of the extrinsic noise of the X-ray detection element 110 at time 160, the signals read at time 244 and time 164 are added and used. By using this addition signal, non-integral extrinsic noise can be corrected by the same signal processing as in the first embodiment, for example. In order to estimate the integral extrinsic noise, a signal obtained by adding the signals of the extrinsic noise detector 184 read out during one frame is created as in the second embodiment. Unlike the signal of the extrinsic noise detector 184 read at the same time as the signal reading time of the X-ray detection element 110, the signals read non-simultaneously are also added. For example, the addition signal used for the integral type extrinsic noise estimation of the X-ray detection element 110 that reads out the signal at the readout time 210 is the signal acquired at the readout times 164, 245, 165, 246, 166, 247, 167, 248, 214. Is obtained by adding all of the above. By using this added value, for example, by performing the same processing as in the second embodiment, the integral type exogenous noise can be corrected.

  Further, as in the third embodiment, fitting may be performed on the extrinsic noise signal to obtain an approximate function, and non-integral or integral extrinsic noise may be estimated and corrected using this function. At this time, in the reading of the present embodiment, the number of readings of the extrinsic noise signal can be increased as compared with the third embodiment, so that the SNR of the fitting function can be improved and the estimation accuracy of the extrinsic noise can be improved.

  In this embodiment, the addition signal is used to estimate non-integral extrinsic noise, but the present invention is not limited to this. As in the first embodiment, the extrinsic noise of the X-ray detection element 110 may be estimated using only the signal of the extrinsic noise detection element 181 read out at the same time.

(Example 7)
The X-ray CT apparatus of the seventh embodiment differs from the element structure of the X-ray detector 104 of the first or second embodiment in that the element structure of the X-ray detector is different from that of the X-ray detector 104 in that the function of amplifying the generated charge amount Have every 110. FIG. 17 is a circuit diagram of an example of such an X-ray detector 104, and FIG. 18 is an explanatory diagram for explaining the control timing of the X-ray detector 104 and the extrinsic noise detector 184. However, this circuit configuration and control timing are merely examples, and do not limit the present invention.

  Compared to the first embodiment (FIG. 3), the X-ray detector 104 shown in FIG. 17 includes a reset switch 250 for turning on / off the reset potential supply and a MOS in which a current depending on the output potential of the photodiode 140 flows. A device 251; a reset power pad 341 for supplying a reset potential; and a reset control pad 252-j for controlling ON / OFF of a reset switch 250-j of the j-th slice. A photodiode 140, a reset switch 250, a MOS device 251, and a switching element 134 are included.

  With such a configuration, a signal generated by X-rays can be read out. When X-rays enter the X-ray detection element 110, charges are generated in the photodiode 140, and a voltage is generated by accumulating this in the capacitor. When the switching element is ON, a current dependent on this voltage is supplied to the current-voltage converter 124. If the integration time of the current-voltage converter 124 is appropriately set, more charge than the charge stored in the photodiode 140 can be stored in the current-voltage converter 124, and a voltage signal corresponding to this charge is used for the signal. It can be obtained from the pad 120. Therefore, a signal depending on the incident X-ray dose can be obtained.

  Next, read timings of the X-ray detector 104 and the extrinsic noise detector 184 of an example of this embodiment will be described with reference to FIG. The signal 150-i in FIG. 18 is supplied to the control pad 133-j in FIG. 17, the signal 259-j is supplied to the reset control pad 252-j, and the signal 151 is the extrinsic noise detector shown in FIG. 184 control pads 188 are supplied.

  Reading of the X-ray detector 104 is performed for each slice. For example, after the first slice is read at time 160, the second slice is read at time 161. Simultaneously with this reading, the external noise detector 184 is read. For example, the reading of the extrinsic noise detector 184 (time 164) is performed simultaneously with the reading of the X-ray detection element 110-i-1 in the first slice (time 160). Immediately after the readout of the X-ray detector 104, the reset switch 250 is turned on to apply the potential applied to the reset power pad 341 to the photodiode 140 in order to reset the charge accumulated in the photodiode 140. . For example, immediately after reading the X-ray detection element 110-i-1 in the first slice at time 160, the reset switch 250-1 is turned on at time 260 to reset the charge of the photodiode 140-i-1. I do.

  By using the signal of the extrinsic noise detector 184 thus read out, the signal of the X-ray detector 104 is corrected by the method shown in the first embodiment and / or the second embodiment, for example. Realize the correction.

  In the present embodiment, a detector without an amplification function is used as the extrinsic noise detector 184, but the present invention is not limited to this, and a detector having an amplification function may be used. In this case, for example, as shown in FIG. 19, an extrinsic noise detector 184 having an amplification function may be used in the same circuit as the X-ray detector 104. Here, the extrinsic noise detector 184 shown in FIG. 19 has a reset switch 255 for turning ON / OFF the reset potential supply and a photodiode 190 as compared with the extrinsic noise detector 184 shown in FIG. The extrinsic noise detecting element 181 includes a MOS device 256 in which a current depending on the output potential flows, a reset power pad 257 for supplying a reset potential, and a reset control pad 258 for controlling ON / OFF of the reset switch 255. 1 includes a photodiode 190, a reset switch 255, a MOS device 256, and a switching element 191.

  The extrinsic noise detecting element 181 shown in FIG. 19 can be controlled, for example, at the timing shown in FIG. Here, the signal 320 is a control signal input to the control pad 258. As shown in FIG. 19, the photodiode 190 is reset simultaneously with the resetting of the photodiode 140 of the X-ray detection element. By performing resetting at the same time, the extrinsic noise caused by fluctuations in reset power and the like can be measured in the same manner by the X-ray detector 104 and the extrinsic noise detector 184. A signal having a strong correlation can be obtained.

  In this embodiment, the X-ray detector 104 and / or the extrinsic noise detector 184 is a detector having a function of amplifying the charge amount for each pixel. However, the present invention is not limited to this, and the pixel In some cases, each pixel has an amplifying function for amplifying the voltage generated in the pixel. In addition, there may be an amplification function in units of a plurality of pixels.

(Example 8)
The X-ray CT apparatus of the eighth embodiment is different from the X-ray CT apparatus of the first or second embodiment in the extrinsic noise detector 184, and the extrinsic noise detector 184 uses an X-ray detector having a defect element. Realized. Here, the defect element means that the X-ray sensitivity, the zero level (offset level), etc. are significantly different from other elements, or the output characteristics with respect to the input of X-rays, etc. This is an element that has been determined to be inappropriate for use because of its physical characteristics, etc. Detectors having such defect elements occur during the manufacturing stage, during movement, during use, etc., and such detectors are often discarded. Using an external noise detector that is the same detector as the X-ray detector and that is not used as an X-ray detector due to defects is advantageous in terms of price.

  FIG. 21 is a diagram showing an example of the extrinsic noise detector 184 of the present embodiment, which is realized by an X-ray detector having a defect element. Here, the defect element is an element at a position represented by the oblique line 330. Specifically, the exogenous noise detection elements 181-1-1, 181-1-2, 181-1-3, 181-2- 3 is a defect element. The extrinsic noise detector 184 is disposed outside the X-ray irradiation field or in a place where X-rays are shielded, or has an X-ray shield in front of the detection surface.

  The estimation of the extrinsic noise is performed using a signal other than the defect element of the extrinsic noise detector 184, for example. For example, extrinsic noise measurement is performed using some of the normal elements of the detector. In this case, for example, the signal 151 of FIG. 6 is input only to the control pad 188-4 of FIG. 21, and the extrinsic noise detection elements 181-1-4 and 181 are transmitted from the electrode pad 185-1 and the electrode pad 185-2. Reads the signal of -2-4. The extrinsic noise correction shown in the first or second embodiment can be realized by using a signal obtained by analog-digital conversion of this signal and using, for example, a signal obtained by averaging the signals.

  In the present embodiment, only elements of the same slice are used, but the present invention is not limited to this. For example, a signal of the same channel element may be used. In this case, for example, the same signal is input to the control pad 188-1 and the control pad 188-1, and is generated from the electrode pad 185-2 to the extrinsic noise detection elements 181-2-1 and 181-2-2. An addition signal of the obtained signals may be used. In addition, by switching the signal 151 to one of the control pad 188-1 and the control pad 188-1 and switching it, the external noise detection element 181-2-1 or 181-2-2 reads the signal 151, respectively. The output signal may be used. Furthermore, elements may be selected regardless of the channel and slice. For example, the signal 155 is input to the control pad 188-1, the control pad 188-1, and the control pad 188-4, and the signal is obtained from the electrode pad 185-1 and the electrode pad 185-2. At this time, addition signals of the extrinsic noise detection elements 181-2-1, 181-2-2, and 181-2-4 are obtained from the electrode pad 185-2. The added signal of the extrinsic noise detection elements 181-1-1, 181-1-2, and 181-1-4 can also be obtained from the electrode pad 185-1, but the extrinsic noise detection elements should not be used. The output lines of the noise detection elements 181-1-1 and 181-1-2 are disconnected so that they are not output simultaneously. A signal obtained by adding the analog-digital converted signal and dividing the signal of the electrode pad 185-1 and the electrode pad 185-2 at this time by the number of elements may be used for extrinsic noise correction.

  Further, if possible, signals are acquired using the extrinsic noise detection element 181 of the same slice as the slice from which the X-ray detector 104 is read, and other slices in which there is no usable extrinsic noise detection element 181 Signals obtained using the extrinsic noise detection element 181 of the slices may be acquired and extrinsic noise correction may be performed. As an example for explaining this, the case where the extrinsic noise correction is performed using the extrinsic noise detector 184 of FIG. 21 and the output from the electrode pad 185-2 as the output from the second channel will be described. .

  FIG. 28 shows an example of control timing. In the first, second, and fourth slices, signals of the same slice of the extrinsic noise detector 184 and the X-ray detector 104 are acquired simultaneously. That is, the time 160 for reading the X-ray detection element 110 in the first slice and the time 164 for reading the extrinsic noise detection element 181 in the first slice are the same. Similarly, the time 161, the time 165, the time 163 and time 167 are simultaneous. However, since the extrinsic noise detection element 181-1-3 in the third slice is a defect element, the extrinsic noise cannot be acquired using the extrinsic noise detection element 181 in the same slice as the X-ray detector 104. For this reason, the extrinsic noise signal of the third slice is acquired using another slice. In FIG. 28, for example, the extrinsic noise of the X-ray detection element 110 of the third slice is acquired using the extrinsic noise detection element 181 of the fourth slice, and the time 162 and the time 166 are the same. By performing the control in this way, the extrinsic noise detection element 181 for measuring the extrinsic noise is switched between using the same readout slice as the X-ray detector 104 and using a different slice to reduce the extrinsic noise. Can be acquired.

  In this embodiment, extrinsic noise correction is performed without using the output of the defect element, but the present invention is not limited to this. Since the X-ray detector 104 and the extrinsic noise detector 184 have different characteristics and accuracy, the X-ray detector 104 and the extrinsic noise detector 184 may be usable as the extrinsic noise detecting element 181 even when the X-ray detecting element 110 cannot be used. For example, while the X-ray detection element 110 requires a wide dynamic range, the extrinsic noise detection element 181 measures almost an offset level (zero level) and does not require a wide dynamic range. Therefore, an X-ray detection element can be used as the extrinsic noise detection element 181 even if it is determined to be a defect element due to a narrow dynamic range, or an element determined to be a defect element due to output characteristics with respect to an input X-ray. There may be possible elements.

Example 9
The X-ray CT apparatus according to the ninth embodiment is different from the X-ray CT apparatus according to the first or second embodiment in that the extrinsic noise detector is used, and the control signal of the switching element 191 that controls the reading of the X-ray detector 104 is used. , The switching element 191 of the extrinsic noise detector 184 is controlled. An explanatory diagram for explaining the X-ray detector 104 and the extrinsic noise detector of this embodiment is shown in FIG.

  The extrinsic noise detecting element 181 of the present embodiment is formed on the back surface of the X-ray detector 104 as shown in FIG. Here, FIG. 22 shows a circuit diagram 104-f of the X-ray detector 104 viewed from the X-ray incident direction and a circuit diagram 104-b on the back thereof. The control line of the switching element 191 of the extrinsic noise detection element 181 is connected to the control line of the X-ray detection element 110 of slice j via the changeover switch 350-j. The gate electrode of the changeover switch 350-j is electrically connected to the control pad 351-j. Accordingly, when an ON control signal is input to the changeover switch 350-j, the control line of the X-ray detection element 110 of the slice j where the ON signal is present and the control line of the extrinsic noise detection element 181 are electrically connected.

  By forming the extrinsic noise detecting element 181 on the back surface of the X-ray detector 104, it becomes possible to arrange the exogenous noise detecting element 181 near the X-ray detector 104. A signal having a strong correlation with the X-ray detector can be obtained by the extrinsic noise detection element, and high-precision correction can be realized. Furthermore, since the X-ray detector acts as an X-ray shield, it is not necessary to provide a separate X-ray shield.

  Using such a configuration, the reading of the extrinsic noise detection element 181 is controlled using the control signal of the slice from which the X-ray detector 104 reads. That is, when reading the X-ray detection element 110 in the jth slice, an ON control signal is input to the control pad 351-j. By such control, the extrinsic noise detection element 181 can be read using the same control signal as the X-ray detection element 110 that performs reading. Therefore, even when the control line fluctuates due to the extrinsic noise factor and this causes the extrinsic noise in the X-ray detection element 110, the extrinsic noise detection element 181 can measure the extrinsic noise in the same manner. Noise correction can be performed. Therefore, it is possible to accurately correct the extrinsic noise due to the fluctuation of the control line of the X-ray detection element 110.

  In this embodiment, the input control signal to the extrinsic noise detecting element 181 is switched by the circuit configuration changeover switch 350 in FIG. 22, but the present invention is not limited to this, and various circuit configurations are possible. . For example, there may be a circuit configuration of the changeover switch 350 as described in the tenth embodiment.

  In this embodiment, the X-ray detector 104 has a structure in which the exogenous noise detection element 181 is mounted on the back surface, but the present invention is not limited to this. For example, there may be a case where the extrinsic noise detection element 181 is provided in front of the X-ray detector 104, or a case where the X-ray detector 104 and the extrinsic noise detector 184 are provided on different substrates.

(Example 10)
The X-ray imaging apparatus of Embodiment 10 is an embodiment of the present invention in an X-ray DR apparatus equipped with a flat panel detector. FIG. 23 is an explanatory diagram illustrating an example of an embodiment of the X-ray DR apparatus according to the present embodiment. FIG. 24 is an explanatory diagram showing an example of the flat panel detector 104 and the extrinsic noise detector 184 of the present embodiment. 25 and 26 are explanatory diagrams for explaining an example of read timing at the time of moving image shooting. FIG. 27 is an explanatory diagram for explaining an example of read timing at the time of still image shooting.

  As shown in FIG. 23, as the basic configuration of the X-ray DR apparatus of the present embodiment, an X-ray tube 100 that irradiates X-rays, an X-ray detector that detects X-rays and converts them into electrical signals (flat panel detector) 104) From the extrinsic noise detector 184 that detects the extrinsic noise and converts it into an electrical signal, from the signal collecting means 118 that collects signals from the flat panel detector 104 and the extrinsic noise detector 184, from the signal collecting means 118 Central processing means 105 for storing image data and performing image processing, display means 106 for displaying the results of image processing, input means 119 for starting imaging, setting parameters, and inputting, X-ray tube 100, flat panel detector 104 , Control means 117 for controlling the extrinsic noise detector 184.

  In imaging, first, imaging start is input from the input means 119, and X-rays are emitted from the X-ray source 100 toward the subject 102. A part of this X-ray passes through the object 102 and is detected by the X-ray detector 104 to generate an electric signal depending on the X-ray dose. This electric signal is AD converted by the signal collecting circuit 118 to become a digital signal. In this imaging, a collection of digital signals obtained from a large number of X-ray detection elements of the X-ray detector 104 constitutes one projection image. In synchronization with the acquisition of the X-ray detection signal, the signal is read using the extrinsic noise detector 184. At this time, the extrinsic noise signal generated by the extrinsic noise factor is acquired. This signal is also converted into a digital signal by analog-digital conversion (AD conversion) by the signal collecting circuit 118. Next, the central correction circuit 105 performs image correction processing on the digital signal of the X-ray detection signal. The correction process is, for example, the sensitivity correction process or the offset correction process described in the first embodiment, or the extrinsic noise correction described in the first and second embodiments. The result is displayed on the display means 106.

  A circuit configuration of the flat panel detector 104 and the extrinsic noise detector 184 as an example of the embodiment of the present invention will be described with reference to FIG. Here, the flat panel detector 104 is provided with an X-ray detection element 110 in a matrix of 6 rows and 4 columns. However, these numbers are merely examples, and the present invention is not limited thereto. One extrinsic noise detection element 181 is installed as the extrinsic noise detector 184, but this number is an example of implementation, and the present invention is not limited to this.

  The X-ray detection element 110 of the flat panel detector 104 of this embodiment is composed of a photodiode 140 and a switching element 134. The gate electrode of the switching element is connected to the vertical shift register 334 by a common control line for each row. Therefore, when an ON signal is output from the vertical shift register 334 to the switching element, the electrical signals of the X-ray detection elements 110 belonging to the same row are read out simultaneously. The output signal is input to the current-voltage converter 124 to become a voltage signal and input to the parallel-serial converter 335. The parallel-serial converter 335 outputs the signals to the signal collecting unit 118 in order for each column, for example, the first column, the second column, the third column, and the fourth column while holding the signals of all columns. The signal collecting means 118 converts the signals in each column into digital signals.

  The control signal of the vertical shift register 334 is also input to the extrinsic noise detection element 181 via the changeover switch 350. The extrinsic noise detection element 181 includes a photodiode 190 that generates and stores an extrinsic noise signal, and a switching element 191 that turns ON / OFF reading of the stored signal, and is output from the vertical shift register 334. Reading is controlled by the control signal. The changeover switch 350 inputs the control signal of the row to which the ON signal is input to the extrinsic noise detection element 181. Therefore, the extrinsic noise detection element 181 reads the signal simultaneously with the signal reading of the X-ray detection element 110 in each row. Similar to the X-ray detector 104, the read signal is converted into a voltage signal by the current-voltage converter and output to the signal collecting means 118.

  Next, the vertical shift register 334 outputs an ON signal to the X-ray detection elements 110 in different rows and performs the same reading. Thereafter, all the X-ray detection elements 110 of the flat panel detector 104 can be read by switching the rows to be read sequentially, and the signals of the extrinsic noise detection elements 181 are read in synchronization with the respective signal readings. .

  The changeover switch 350 according to the present embodiment is supplied with a power amount from the voltage source 337 and has a current source circuit 338 so that the MOS transistor that performs switching is in a saturation region, thereby forming a source follower circuit. Therefore, the voltage input to the gate electrode can be output to the source electrode almost as it is (lowered by the threshold voltage). However, this is an example, and the present invention is not limited to this. For example, there may be a circuit configuration shown in the ninth embodiment.

  In this embodiment, the case where the X-ray detector 104 and the extrinsic noise detector 184 are provided on separate substrates is described, but the present invention is not limited to this. In some cases, both may be provided on an integrated substrate, or as in the ninth embodiment, the extrinsic noise detector 184 may be provided on the back surface of the X-ray detector 104 substrate. Further, although the exogenous noise detector 184 is disposed adjacent to the side of the X-ray detector 104, the present invention is not limited to this. In some cases, it may be arranged. In the present embodiment, the case where there is one extrinsic noise detector 184 is shown, but the present invention is not limited to this. There may be a case where a plurality of exogenous noise detectors 184 are received at one place, or a case where they are provided at a plurality of places.

  In general, an X-ray DR apparatus has imaging functions for both moving image shooting (perspective shooting) and still image shooting (general shooting, simple shooting). An example of each photographing sequence will be described with reference to FIGS. In each figure, a signal 150-j is a control signal for controlling the signal readout of the X-ray detection element 110 in slice j, a signal 151 is a control signal for controlling the signal readout of the extrinsic noise detection element 181, and a signal 331 Is a signal for controlling X-ray irradiation of the X-ray tube 100 (shown in FIG. 1), time 365 is the imaging start time, and time 152 is the length of one frame. Here, the number of shooting frames shown in FIGS. 25 and 26 is for simplifying the description, and does not limit the present invention.

  In moving image shooting, there are continuous fluoroscopic imaging using continuous X-rays and pulsed fluoroscopic imaging using pulsed X-rays. As shown in FIG. 25, the continuous fluoroscopic imaging is an imaging in which, after an imaging start input, X-ray irradiation is started from an imaging start time 365, irradiation is continuously performed for a plurality of frames, and a generated signal is read out for each frame. is there. As shown in FIG. 26, the pulse fluoroscopy is performed in such a manner that the X-ray irradiation is turned on and off during the blanking time 332 before the reading is finished in each frame after entering the imaging start and before entering the next frame. X-ray irradiation, and the operation of sequentially reading the generated signals in the post-irradiation frame is repeated. The extrinsic noise is read out in synchronism with this signal reading, and the central processing means 105 uses the signal to read the digital signal of the X-ray detection signal, for example, the extrinsic described in the first and / or the second embodiment. Noise correction is performed, and the result is continuously displayed on the display means 106.

  In still image shooting, as shown in FIG. 27, after input of imaging start, X-ray irradiation is started from imaging start time 365, and the generated signal is read out. In synchronization with this signal readout, the extrinsic noise is read out, and the central processing unit 105 uses the signal to detect the extrinsic noise described in the first and / or second embodiments, for example, for the X-ray detection data. Make corrections and save the results. The corrected image is displayed on the display means 106.

  The analog signal processing shown in this embodiment is an example of the embodiment, and the present invention is not limited to this. For example, in this embodiment, the analog signal is converted from analog to digital after parallel-serial conversion, but parallel-serial conversion may be performed after analog-to-digital conversion.

In the present embodiment, the case where the X-ray detection element 110 of the flat panel detector is simultaneously read for each row is described, but the present invention is not limited to this. In the case of simultaneous reading for each column, or in the case of multiple rows of columns, multiple columns or multiple rows may be read simultaneously. Further, the structure of the X-ray detection element 110 of the flat panel detector shown in this embodiment is an example, and the present invention is not limited to this. For example, there may be various structures such as a structure having an amplification function as shown in the seventh embodiment.

  In the present embodiment, the case where the extrinsic noise correction in the moving image is applied to the X-ray DR apparatus has been described, but the present invention is not limited to this. It can be applied to various devices capable of capturing moving images, equipped with a detector that acquires signals by switching the detection element that performs reading. For example, there may be various devices such as various devices that do not store moving images in the central processing unit 105, and devices that store moving images continuously, such as a cone beam CT device. Alternatively, the present invention can be applied to various devices capable of taking still images, such as digital X-ray image taking devices.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. Further, the above embodiment includes various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed components. For example, some components may be deleted from all the components shown in the embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows an example of the X-ray CT apparatus by this invention. Explanatory drawing of an example of the X-ray detector used for the X-ray CT apparatus of this invention. Explanatory drawing of an example of the circuit of an X-ray detector. The figure explaining an example of arrangement | positioning of an X-ray detector and an extrinsic noise detector. The circuit diagram which shows an example of an extrinsic noise detector. The figure explaining the signal read-out timing of an X-ray detector and an extrinsic noise detector. The figure explaining an example of a process of a central processing means. The figure explaining an example of an exogenous noise removal process. The figure explaining an example of an exogenous noise removal process. The figure explaining an example of the exogenous noise estimation method. Explanatory drawing which shows an example of an extrinsic noise detector. Explanatory drawing which shows an example of an extrinsic noise correction process. Explanatory drawing which shows an example of an extrinsic noise detector. The figure explaining an example of the control timing of an exogenous noise detector. The figure explaining an example of the control timing of an exogenous noise detector. The figure explaining an example of the control timing of an exogenous noise detector. The circuit diagram of an example of an X-ray detector. The figure explaining an example of the control timing of an exogenous noise detector. The circuit diagram of an example of an exogenous noise detector. The figure explaining an example of the control timing of an exogenous noise detector. The circuit diagram of an example of an exogenous noise detector. Explanatory drawing of an X-ray detector and an extrinsic noise detector. Explanatory drawing which shows an example of an X-ray DR apparatus. Explanatory drawing which shows an example of a flat panel detector and an extrinsic noise detector. The figure explaining an example of the signal read-out timing in a X-ray DR apparatus. The figure explaining an example of the signal read-out timing in a X-ray DR apparatus. The figure explaining an example of the signal read-out timing in a X-ray DR apparatus. The figure explaining an example of the control timing of an exogenous noise detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... X-ray source, 101 ... Rotating body, 102 ... Subject, 103 ... Bed top plate, 104 ... X-ray detector, 105 ... Central processing means, 106 ... Display means, 107 ... Rotation axis direction (slice direction), 108 Rotational direction (channel direction), 110 X-ray detection element, 111 Photoelectric conversion substrate, 112 Scintillator element, 113 Wiring substrate, 117 Control unit, 118 Signal collection unit, 119 Input unit, 120 Electrode Pad, 124 ... Current-voltage converter, 130 ... Separator, 133 ... Control pad, 134 ... Switching element, 135 ... Ground electrode pad, 140 ... Photodiode, 141 ... Ground line, 142 ... Signal line, 143 ... Control line, 150 ... X-ray detector control signal, 151 ... extrinsic detector control signal, 152 ... time of one frame, 160 to 167, 2 0 to 217, 224 to 227, 234 to 237, 244 to 248, 260 to 267, 310 to 317 ... time, time, 168 ... overlap time, 180 ... photoelectric conversion substrate, 181 ... extrinsic noise detection element, 182 ... wiring Substrate, 183 ... X-ray shielding plate, 184 ... extrinsic noise detector, 185 ... electrode pad, 186 ... current-voltage converter, 187 ... ground electrode, 188 ... control pad, 189 ... dark box, 190 ... photodiode, 191 ... switching element, 201 ... fitting curve, 250 ... reset switch, 251 ... MOS device, 252 ... control pad, 255 ... reset switch, 256 ... MOS device, 257 ... reset power pad, 258 ... reset control pad, 259 ... Reset control signal, 270 ... extrinsic noise detector output value, 271 Elapsed time 301... Correction means 302. Reconstruction means 303. Detector characteristic storage means 310. Blanking time, 334 ... Vertical shift register, 335 ... Parallel serial converter, 337 ... Voltage source, 338 ... Current source circuit, 341 ... Reset power pad, 350 ... Changeover switch, 351 ... Control pad, 365 ... Shooting start time , 406 ... X-ray incident direction, 407 ... Detector characteristic extraction means, 408 ... Exogenous noise estimation means, 409 ... Correction processing means, 410 ... Exogenous noise measurement value storage means, 411 ... X-ray detector output storage means, 412 ... Estimation result storage means, 413 ... Addition means, 414 ... Addition averaging means, 415 ... Sensitivity / offset correction means

Claims (13)

An X-ray source that emits X-rays;
An X-ray comprising a plurality of X-ray detection elements that detect X-rays transmitted through the subject and convert them into electrical signals, and an X-ray signal readout circuit that reads detection signals from the X-ray detection elements and converts them into digital signals. Detection means;
Noise measuring means comprising a noise measuring element that generates an electric signal due to an extrinsic noise factor, and a noise readout circuit that reads the extrinsic noise signal from the noise measuring element and converts it into a digital signal;
Computing means for computing extrinsic noise contained in the digital signal of the X-ray detection means using the digital signal of the noise measuring means;
Correction means for performing correction processing on the digital signal of the X-ray detection means using the calculation result of the calculation means;
The X-ray detection means switches the X-ray detection element that performs detection signal readout a plurality of times by the X-ray signal readout circuit, and acquires data for one X-ray image,
The noise measuring means reads out the extrinsic noise signal of at least one identical noise measuring element while acquiring the data for one X-ray image, and reads out the detection signal of the X-ray detecting element at different times. An X-ray imaging apparatus, wherein the X-ray imaging apparatus performs the same from the noise readout circuit simultaneously and outputs the same to the arithmetic means. 2. The X-ray imaging apparatus according to claim 1, wherein the X-ray detection means includes a plurality of simultaneous X-ray detection means for simultaneously reading detection signals from a plurality of X-ray detection elements by the X-ray signal readout circuit. Then, the simultaneous X-ray detection means is switched M times (M is an integer of 2 or more) to acquire data for one X-ray image,
While the noise measuring means reads out the extrinsic noise signal simultaneously with the detection signal reading by the simultaneous X-ray detecting means and acquires data for one X-ray image, at least one identical noise measuring means includes: An X-ray imaging apparatus, wherein an external noise signal is read from the noise readout circuit simultaneously with detection signal readout of the simultaneous X-ray detection means at different times. 2. The X-ray imaging apparatus according to claim 1, wherein the noise measuring means includes one or more M simultaneous noise measuring means for simultaneously reading extrinsic noise signals from a plurality of noise measuring elements by the noise reading circuit (M is 2). Have an arrangement less than an integer),
The simultaneous noise measurement means reads out the extrinsic noise signal simultaneously with the detection signal read by the X-ray detection means, and acquires at least one identical simultaneous noise measurement means while acquiring data for one X-ray image. An X-ray imaging apparatus characterized in that the exogenous noise signal is read from the noise readout circuit simultaneously with the detection signal readout of the X-ray detection means at different times. 2. The X-ray imaging apparatus according to claim 1, wherein the X-ray detection means includes a plurality of simultaneous X-ray detection means for simultaneously reading detection signals from a plurality of X-ray detection elements by the X-ray signal readout circuit. Then, the simultaneous X-ray detection means is switched M times (M is an integer of 2 or more) to acquire data for one X-ray image,
The noise measuring means has a configuration in which one or more and less than M simultaneous noise measuring means for simultaneously reading out extrinsic noise signals from a plurality of noise measuring elements by the noise reading circuit are arranged,
The simultaneous noise measuring means reads the extrinsic noise signal simultaneously with the detection signal reading by the simultaneous X-ray detecting means, and acquires at least one same simultaneous noise measuring means while acquiring data for one X-ray image. However, the X-ray imaging apparatus reads out the extrinsic noise signal simultaneously from the detection signal of the simultaneous X-ray detection means at different times from the noise readout circuit.   2. The X-ray imaging apparatus according to claim 1, wherein the computing means is based on a digital signal of the noise measuring element that has read out an extrinsic noise signal simultaneously with reading out a detection signal by the X-ray detecting means. An X-ray imaging apparatus characterized by calculating noise.   2. The X-ray imaging apparatus according to claim 1, wherein the calculating means performs the extrinsic noise calculation of the X-ray detection element, and reads the extrinsic noise signal simultaneously with the detection signal reading of the X-ray detection element. An X-ray imaging apparatus characterized by performing a correlation between an element and the X-ray detection element with respect to the extrinsic noise factor.   2. The X-ray imaging apparatus according to claim 1, wherein the calculation means includes a digital signal of the noise measuring element that has read out the extrinsic noise signal simultaneously with reading of a detection signal of the X-ray detecting element and an extrinsic noise signal not simultaneously. An X-ray imaging apparatus, wherein extrinsic noise of the X-ray detection element is calculated using digital signals of one or more noise measurement elements that have been read.   2. The X-ray imaging apparatus according to claim 1, wherein the X-ray detection means periodically reads out signals for the X-ray image for each frame a plurality of times, and the calculation means reads out detection signals of the X-ray detection element. At the same time, the digital signal of the noise measurement element that has read out the extrinsic noise signal and the one or more noise measurement elements that have read out the extrinsic noise signal in a frame different from the detection signal read-out of the X-ray detection element. An X-ray imaging apparatus characterized by calculating extrinsic noise of the X-ray detection element using a digital signal.   2. The X-ray imaging apparatus according to claim 1, wherein the noise measuring means includes X-ray shielding means for preventing X-rays from entering the noise measuring element.   2. The X-ray imaging apparatus according to claim 1, wherein the noise measuring means is arranged adjacent to or close to a surface opposite to the X-ray incident surface of the X-ray detecting means.   2. The X-ray imaging apparatus according to claim 1, wherein the X-ray detection means includes a switching element that controls 0N / OFF switching of signal readout of the X-ray detection element, and a control line that inputs a control signal to the switching element. The noise measuring means includes a switching element for controlling ON / OFF switching of signal readout of the noise measuring element, a control line for inputting a control signal to the switching element, a control line for the noise measuring element, Control line switching means for selectively connecting a control line of the X-ray detection element, the control line switching means comprising: a control line of the X-ray detection element for reading a signal; and the X-ray detection element At the same time, the control line of the noise measuring element that performs reading is connected, and switching control of the noise measuring element is performed using the control signal of the X-ray detecting element. X-ray imaging apparatus according to claim.   2. The X-ray imaging apparatus according to claim 1, wherein the X-ray detection means has a structure in which a plurality of X-ray detection modules each composed of a plurality of X-ray detection elements are arranged, and the noise measurement means is a defect X-ray detection. An X-ray imaging apparatus comprising the X-ray detection module having an element.   2. The X-ray imaging apparatus according to claim 1, further comprising arithmetic processing means for generating a tomographic image by performing reconstruction arithmetic processing on the signal obtained from the correcting means.

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