JP4114717B2 - CT equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a CT apparatus used for industrial nondestructive inspection and medical inspection.
[0002]
[Prior art]
As a technology in such a field, a conventional CT (Computed Tomography) apparatus is configured to accumulate the number of photons and energy by the incidence of a radiation source and a photon irradiated from the radiation source and passing through a subject. And a detector having a semiconductor or a combination of a scintillator and a semiconductor that generates electric charges according to the above. Then, a tomographic image of the subject is reconstructed using a signal corresponding to the integrated value of the charges accumulated in the detector as projection data. Such a method is called a charge integration method.
[0003]
[Problems to be solved by the invention]
In the above-described CT device using the charge integration method, projection data is generated as an integral value of a signal based on charges excited in the semiconductor element by photons in all energy bands. Therefore, in the charge integration type detector, since the signal once integrated cannot be separated for each original incident energy, analysis and visualization using photon energy cannot be performed.
[0004]
The projection data includes components due to low energy multiple scattered photons in addition to components due to primary photons that are useful information. This low-energy multi-scattered photon has a large attenuation, and when the transmission distance of the photon becomes long, a phenomenon called beam hardening that causes a large attenuation occurs even if the density distribution inside the subject is uniform. As described above, there is a problem that an artifact (false image) is generated in a tomographic image generated when beam hardening occurs.
[0005]
In order to solve such problems, conventionally, a method has been adopted in which a low-energy multiple scattered photon is removed by physically installing an aluminum or iron filter in front of the detector. However, such a physical filter has a problem of reducing the number of primary photons that are useful information.
[0006]
The present invention has been made to solve the above-mentioned problems, and has a function of identifying the energy of incident photons on the detector side, and has a new analysis method and visualization technique born by identifying the energy of incident photons. In addition to providing a CT apparatus, a CT apparatus capable of reconstructing an image inside a subject free from artifacts due to beam hardening without using a physical filter.
[0007]
[Means for Solving the Problems]
  In order to solve the above-mentioned problems, a CT apparatus according to the present invention is arranged so as to face radiation irradiation means for irradiating radiation and the radiation irradiation means across a measurement space, and has a predetermined central axis penetrating the measurement space. Each time a photon included in the radiation is incident on each of the plurality of semiconductor elements and the plurality of semiconductor elements arranged in a direction perpendicular to the irradiation direction of the radiation passing through the predetermined central axis. Signal generating means for outputting a signal corresponding to the energy of the incident photon;Multiple predetermined thresholdsA detection means having a counting means for counting the number of the signals having a wave height in a range set based on each of the plurality of semiconductor elements, an object placed in the measurement space, the detection means, and the Based on the rotating unit that changes the relative angle with the radiation irradiating unit for each predetermined angle around the predetermined central axis, and the count value counted by the counting unit, the tomographic image of the subject is reproduced. An arithmetic means for performing the configuration,The radiation irradiating means emits X-rays having a continuous spectrum or a plurality of monochromatic energy radiations each having different energy as the radiation, and the subject has first and second different in at least one of density and element. The counting means includes at least a substance, and the counting means is between two predetermined thresholds predetermined to selectively detect photons of the first energy contained in the radiation among a plurality of predetermined thresholds. Of the plurality of predetermined thresholds, the number of signals having a wave height is different from the two predetermined thresholds, and is determined in advance to selectively detect photons of the second energy contained in the radiation. The number of signals having a wave height between two predetermined threshold values is counted at least for each of the plurality of semiconductor elements, and the first and second energies are different.
[0008]
  According to the CT apparatus of the present invention, the radiation irradiating means for irradiating radiation and the detecting means are provided facing the radiation irradiating means across the measurement space. This detection means has a plurality of semiconductor elements arranged in a direction perpendicular to the axial direction of a predetermined central axis passing through the measurement space and the radiation irradiation direction passing through the predetermined central axis. These semiconductor elements generate charges corresponding to the energy of the photons each time the photons contained in the radiation are incident. And the signal generation means which a detection means has outputs the signal based on said electric charge for every semiconductor element. And the counting means with which the detection means is provided, among the signals output from the signal generation means,Multiple predetermined thresholdsCount the number of signals having a wave height in the range set by. Here, the count value counted by the counting means is obtained by counting the number of photons in a specific energy band corresponding to the set threshold value. The count value for each semiconductor element obtained in this way is used as projection data, and the projection data is obtained by changing the relative angle between the subject, the radiation irradiation means, and the detection means for each predetermined angle by the rotating means. From the other direction. Then, the tomographic image inside the subject is reconstructed using the projection data collected by the calculation means. As described above, since projection data based on the number of photons in a specific energy band is used, projection data excluding low-energy multiple scattered photons can be obtained without using a physical filter. As a result, since the influence of beam hardening can be removed, a tomographic image free from artifacts can be reconstructed.
[0009]
  In order to solve the above-described problem, a CT apparatus according to the present invention is disposed opposite to the radiation irradiating means for irradiating radiation and the radiation irradiating means across the measurement space, and has a predetermined penetration through the measurement space. Each time a photon included in the radiation is incident on each of the plurality of semiconductor elements arranged in a direction parallel to the axial direction of the central axis, a signal corresponding to the energy of the incident photon is output. Signal generating means forMultiple predetermined thresholdsA detection means having a counting means for counting the number of the signals having a wave height in a range set based on each of the plurality of semiconductor elements, an object placed in the measurement space, the detection means, and the Rotating means that changes the relative angle with the radiation irradiating means for each predetermined angle with the predetermined central axis as a center, and relative to the subject, the detecting means, and the radiation irradiating means by the rotating means. Scanning means for scanning the detection means in a tangential direction at the position of the detection means on the circumference including the position where the detection means is arranged around the predetermined central axis each time a specific angle changes And calculation means for reconstructing the three-dimensional image of the subject based on the count value counted by the counting means,The radiation irradiating means emits X-rays having a continuous spectrum or a plurality of monochromatic energy radiations each having different energy as the radiation, and the subject has first and second different in at least one of density and element. The counting means includes at least a substance, and the counting means is between two predetermined thresholds predetermined to selectively detect photons of the first energy contained in the radiation among a plurality of predetermined thresholds. Of the plurality of predetermined thresholds, the number of signals having a wave height is different from the two predetermined thresholds, and is determined in advance to selectively detect photons of the second energy contained in the radiation. The number of signals having a wave height between two predetermined thresholds is counted at least for each of the plurality of semiconductor elements, and the first and second energies are different from each other.

[0010]
According to the CT apparatus according to the present invention, the detection means described above is arranged such that a plurality of semiconductor elements provided therein are arranged in parallel to the axial direction of a predetermined central axis that penetrates the measurement space. Then, the relative angle between the subject, the radiation irradiation unit, and the detection unit is changed by the rotation unit by a predetermined angle about the predetermined center axis. Further, each time the angle is changed by the rotating means, the scanning means moves in the tangential direction at the position of the detecting means on the circumference including the position where the detecting means is arranged around the predetermined central axis. Scan the detection means. Data obtained by one semiconductor element by scanning the detection means is used as projection data, and one tomographic image can be reconstructed by projection data acquired from multiple directions by this one semiconductor element by changing the angle by the rotation means. And also about the projection data acquired by each semiconductor element, if each tomogram is generated in this way, a three-dimensional image of the subject can be reconstructed. In addition, as described above, in this CT apparatus, the number of photons in a specific energy band can be counted by the detection means, so that the influence of beam hardening can be removed, so that an image free from artifacts can be reconstructed. Can do.
[0017]
  In the CT apparatus of the present invention,the aboveRadiation irradiation meansButIrradiate multiple monochromatic energy radiation, each with different energyWhen toThe counting means calculates the number of the signals having a wave height between the predetermined threshold values set in accordance with the energy of the plurality of monochromatic energy radiations among the signals output by the signal generating means. It is preferable that counting is performed for each of the threshold values, and the calculation unit reconstructs a plurality of images based on the count values for the respective threshold values counted by the counting unit. is there.
[0018]
According to the present invention, the number of photons in a specific energy band can be counted by detecting the number of signals having a wave height between two threshold values by the detection means. The number of photons having different energies can be counted independently by irradiating energy radiation and setting two thresholds according to each energy. Therefore, even in a specimen in which high-density substances and low-density substances are distributed, high-energy monochromatic energy radiation suitable for imaging high-density substances with good contrast and low-density substances with good contrast Using low energy monochromatic energy radiation suitable for imaging, both distributions can be imaged simultaneously with good contrast.
[0019]
In the CT apparatus of the present invention, the semiconductor element includes CdTe, CdZnTe, HgI.₂, PbI₂Or GaAs.
[0020]
CdTe, CdZnTe, HgI₂, PbI₂A semiconductor element made of GaAs or GaAs has higher photon collection efficiency than a semiconductor element made of Ge, Si, or the like, and can be downsized. In particular, since CdTe has a large band gap and does not require a cooling device, the element can be made smaller. Therefore, according to these inventions, since a plurality of semiconductor elements can be arranged at a narrow interval, the spatial resolution can be improved.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a CT apparatus according to an embodiment of the present invention will be described. In the following description of the embodiments, for ease of understanding of the description, the same components are denoted by the same reference numerals as much as possible in each drawing, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.
[0022]
(First Embodiment) First, a CT apparatus 1 according to a first embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view of a CT apparatus 1 according to the first embodiment. As shown in FIG. 1, the CT apparatus 1 includes a radiation source (radiation irradiation means) 3, a rotary table (rotation means) 5, and a detector (detection means) 10 on a stage 2. Is connected to a computer (arithmetic unit) 30 via a USB (Universal Serial Bus) cable 30.
[0023]
As shown in FIG. 1, the radiation source 3 emits X-rays toward the subject 7 installed on the turntable 5. In addition, the turntable 5 is a measurement space above, and the subject 7 placed on the upper surface is rotated by a predetermined angle about the central axis 6 penetrating the turntable 5.
[0024]
Next, as shown in FIG. 1, the detector 10 is arranged to face the radiation source 3 with the measurement space above the turntable 5 interposed therebetween. Then, X-rays emitted from the radiation source 3 are detected. FIG. 2 is a perspective view for explaining the configuration of the detector 10. As shown in FIG. 2, the detector 10 includes a plurality of prismatic semiconductor elements 12 made of CdTe (cadmium telluride). The plurality of semiconductor elements 12 are arranged in a direction perpendicular to the axial direction of the central axis 6 shown in FIG. 1 and the irradiation direction of X-rays irradiated by the radiation source 3 and passing through the central axis 6.
[0025]
Returning to FIG. 2, a bias voltage is applied to each of the semiconductor elements 12 with the upper surface serving as the anode 13 and the lower surface serving as the cathode 14. Then, X-rays irradiated from the radiation source 3 are incident, and charges corresponding to the energy of incident photons of the X-rays are generated in the respective semiconductor elements 12. A current signal based on the charge generated in each semiconductor element 12 is output to the pulse counting IC 16.
[0026]
FIG. 3 is a block diagram showing the configuration of the pulse counting IC 16. As shown in FIG. 3, the pulse counting IC 16 converts the current signal output from the semiconductor element 12 into a voltage signal by the preamplifier 21 and amplifies it, and further amplifies this voltage signal by the main amplifier 22. The voltage signal output from the main amplifier 22 is shaped by the waveform shaper 23. Then, the voltage signal shaped by the waveform shaper 23 is output to the comparator 24. The comparator 24 compares the input voltage signal with each of the two reference voltages, and outputs a constant pulse voltage signal to the A / D converter 25 when the wave height of the voltage signal is larger than the respective reference voltages. To do. That is, the comparison result between the above-described two reference voltages and the wave height of the voltage signal is output to the A / D converter 25 as two systems of pulse voltage signals. These two reference voltages are predetermined voltage values for detecting photons in a specific energy band. Then, the A / D converter 25 converts each of the two pulse voltage signals thus output into a digital signal and outputs the digital signal to the scaler 26. The scaler 26 counts the number of pulses included in each digital signal output from the A / D converter 25.
[0027]
FIG. 4A is a graph showing the time variation of the signal 100 output from the semiconductor element 12 and shaped by the waveform shaper 23. 4 (b) and 4 (c) show the timing at which the scaler 26 counts the pulses included in each digital signal. As shown in FIG. 4A, the signal 100 output from the waveform shaper 23 is compared with the reference voltages 101 and 102 in the comparator 24, respectively, and has a pulse voltage higher than the reference voltage. A signal is output from the comparator 24. That is, two pulse voltage signals based on comparison with each of the reference voltages 101 and 102 are output, and each pulse signal is converted into a digital signal by the A / D converter 25, and then the scaler 26 performs FIG. ) And (c), the number of each pulse is counted.
[0028]
Returning to FIG. 1, the detector 10 outputs the count values of the above-described two pulses based on the photons incident on the plurality of semiconductor elements 12 to the computer 31 via the cable 30.
[0029]
The computer 31 obtains the difference between these two count values for each of the plurality of semiconductor elements 12 and sets it as projection data in one direction. The projection data thus obtained, that is, the difference value between the two count values, indicates the number of photons in a specific energy band incident on the semiconductor element 12. Then, every time the turntable 5 rotates by a predetermined angle, this projection data is collected to collect multi-directional projection data, and a reconstruction operation in known CT is performed using the collected projection data. Thus, a tomographic image of the subject 7 is generated. The computer 31 controls the bias voltage applied to the semiconductor element 12, the threshold applied to the comparator 24, the shaping time applied to the waveform shaper 23, the exposure time, and the like via this cable 30.
[0030]
As described above, the CT apparatus 1 according to the present embodiment counts the number of photons in a specific energy band and uses the tomogram of the subject 7 even if X-rays having a spectrum width are used as the radiation source 3. Since it can be reconstructed, a tomographic image similar to that when irradiating monochromatic energy γ rays can be obtained. In addition, since the number of photons in a specific energy band can be counted, the influence of low energy multiple scattered photons can be eliminated. Therefore, since there is no influence by beam hardening, a tomographic image free from artifacts can be obtained. Furthermore, since only the number of photons in a specific energy band can be counted, signals without noise can be collected over a long period of time, so that the S / N ratio can be improved.
[0031]
Although the photon detection efficiency of X-rays and γ-rays generally tends to increase with the atomic number, CdTe constituting the semiconductor element 12 is a compound semiconductor of Cd of atomic number 48 and Te of 52, and silicon (atom The photon detection efficiency is much higher than that of No. 14). Furthermore, since CdTe has a large band gap, it can be used at room temperature without the need for a cooling device, so that the semiconductor element 12 can be miniaturized. Therefore, since the semiconductor elements 12 can be arranged at a narrow interval, the spatial resolution can be increased. The semiconductor element 12 includes CdZnTe, HgI instead of CdTe.₂, PbI₂Semiconductors with high detection efficiency such as GaAs can also be applied.
[0032]
(Second Embodiment) Next, a CT apparatus 1 according to a second embodiment of the present invention will be described. FIG. 5 is a perspective view of the CT apparatus 1 according to the second embodiment. As shown in FIG. 5, the CT apparatus 1 includes a radiation source 3, a scanning mechanism (scanning means) 4, a rotating table 5, a detector 10, and a scanning mechanism (scanning means) 11 on a stage 2. Data measured by the detector 10 is output to the computer 31 via the signal cable 30.
[0033]
The radiation source 3 is a radiation source similar to the radiation source 3 described in the first embodiment. The detector 10 has a plurality of semiconductor elements 12 arranged in parallel to the axial direction of the central axis 6 that penetrates the measurement space above the turntable 5, and the function thereof is the detector 10 described in the first embodiment. It is the same. The turntable 5 also has the same function as the turntable 5 described in the first embodiment.
[0034]
The scanning mechanism 4 and the scanning mechanism 11 scan the radiation source 3 and the detector 10 in synchronization each time the subject 7 is rotated about the central axis 6 by a predetermined angle by the turntable 5. This scanning direction is a tangential direction of the position of the detector 10 on the circumference including the position where the detector 10 is arranged around the central axis 6.
[0035]
The computer 31 collects the count value counted by the scaler 26 for each position scanned by the scanning mechanism 11 as described in the first embodiment, based on the current signal output by one semiconductor element 12. Let it be projection data. Each time the subject 7 is rotated by the turntable 5, a tomographic image of the subject 7 is reconstructed using the projection data obtained by scanning one semiconductor element 12. A plurality of such tomographic images are generated based on each projection data obtained by scanning each of the plurality of semiconductor elements 12. The computer 31 generates a three-dimensional image from the tomographic images generated in this manner.
[0036]
Thus, according to the second embodiment, a three-dimensional image inside the subject 7 can be reconstructed. Further, as described in the first embodiment, a tomographic image similar to the case of irradiating monochromatic energy γ-rays can be obtained even if X-rays having a wide spectrum are used for the radiation source 3. In addition, as a result of removing the influence of multiple scattered photons, the influence of beam hardening is eliminated and a tomographic image free from artifacts can be obtained.
[0037]
Moreover, since the semiconductor element 12 made of CdTe that can be reduced in size is used, the semiconductor elements 12 can be arranged at a narrow interval to increase the spatial resolution. The semiconductor element 12 includes CdZnTe, HgI instead of CdTe.₂, PbI₂Semiconductors with high detection efficiency such as GaAs can also be applied.
[0038]
Although the first and second embodiments have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, only one reference voltage may be given to the above-described comparator 24 in order to eliminate the influence of low-energy multiple scattered photons. Even in this case, the count value output from the scaler 26 is the photon count value excluding the low-energy multiple scattered photons, and thus the influence of the beam hardening described above is eliminated.
[0039]
Further, according to the concept of the present invention, the detector 10 can independently count the number of photons in a predetermined energy band, and the following modifications are possible. For example, a plurality of monochromatic energy γ rays having different energies are emitted from the radiation source 3, and the detector 10 applies two reference voltages to the comparator 24 according to the energy of each of the monochromatic energy γ rays. Thus, the number of photons having different energy can be counted independently. According to this modification, even if a high-density substance and a low-density substance are distributed inside the subject 7 such as the bones and teeth around the human body and the reinforcing steel in the concrete, the high-density substance The distribution of both low-density materials and low-density substances can be visualized with a good contrast and their boundaries can be visualized clearly. That is, a high-energy monochromatic energy radiation suitable for imaging a high-density material with good contrast and a low-energy monochromatic energy radiation suitable for imaging a low-density material with high contrast are irradiated from the radiation source 3. By doing so, both distributions can be imaged simultaneously with good contrast. Note that the radiation source 3 has an emission line spectrum suitable for imaging each component of the subject 7 with good contrast, and it is necessary to select an RI that generates a spectrum separated by more than the energy resolution of the detector 10. There is. As an example, ytterbium 169, europium 152, barium 133, or the like can be used as a radiation source. In addition, as RI, it is also important to select a nuclide with a long half-life in order to enable stable measurement for a long time, and to select a peak with high emissivity in order to shorten the measurement time.
[0040]
Further, instead of a plurality of monochromatic energy γ rays having different energies, X-rays having a continuous spectrum may be irradiated from the radiation source 3. In this case, two reference voltages are applied to the comparator 24 so as to detect photons in an energy band suitable for imaging the distribution of the high-density substance, and the voltage signal output from the waveform shaper 23 is supplied. Of these, the number of signals having a wave height between these reference voltages is counted and used as projection data, thereby visualizing the distribution of the high-density substance. Further, two reference voltages are given to the comparator 24 so as to detect photons in an energy band suitable for imaging the distribution of the low density substance, and among the voltage signals output from the waveform shaper 23, The number of signals having a wave height between the reference voltages is counted and used as projection data, thereby visualizing the distribution of the low-density substance. Thereby, also about the subject 7 in which a high-density substance and a low-density substance are distributed, both distributions can be obtained simultaneously with good contrast.
[0041]
Further, in order to visualize the distribution of a specific element contained in the subject 7, the K absorption edge of this element can be used as follows. FIG. 6 is a graph for explaining the K absorption edge energy of an element. In FIG. 6, the horizontal axis indicates the photon energy, and the vertical axis indicates the absorption coefficient. The characteristics of the change of the absorption coefficient with respect to the photon energy of each of the three elements A, B, and C are shown. Here, in the characteristic 201 of the element B, the point at which the absorption coefficient is discontinuous is the K absorption edge of the element B, and the characteristics 200 and 202 of the elements A and C are energy in the vicinity of the K absorption edge energy, respectively. There is no change in the absorption coefficient. Therefore, the reference voltage corresponding to the energy 204 higher than the K absorption edge energy and the reference voltage corresponding to the energy 203 lower than the K absorption edge energy are supplied to the comparator 24, and the voltage signal output from the waveform shaper 23. The scaler 26 counts the number of pulses included in the two-system pulse voltage signals that are compared with the respective reference voltages and output by the comparator 24. Then, if the difference value of these count values is used as projection data and the image is reconstructed by the computer 31, the distribution of the element B can be visualized. That is, when the difference is taken as described above, since the change in the absorption coefficient between the energy before and after the K absorption edge energy is small for the elements A and C, the count value is canceled out. The element B contributes. Therefore, an image obtained by reconstructing the difference value as projection data represents the distribution of the element B. For example, when imaging the distribution of gold (Au) contained in an electronic component, the K absorption edge energy of gold (Au) is 80.7 [keV]. When two reference voltages are applied to the comparator 24 so as to detect photons with energy equal to or higher than keV], the scaler 26 outputs count values of photons with energy higher than each energy, and projects the difference between these count values. By performing reconstruction as data, it is possible to visualize the distribution of gold (Au) contained in the electronic component described above.
[0042]
In addition, instead of taking the difference value in this way, an image in which a count value of photons with energy lower than the above K absorption edge energy is reconstructed as projection data, and a count value of photons with energy higher than this K absorption energy It is also possible to visualize the distribution of a specific element contained in the subject 7 having this K absorption edge energy by generating a difference image with an image reconstructed as projection data.
[0043]
In addition, when imaging the distribution of a specific element in the subject 7 using the K absorption edge as described above, an X-ray source may be used as the radiation source 3, but compared with an X-ray source. It is preferable to use RI with little contribution of other wavelengths and scattered rays. For example, in order to visualize the distribution of gold (Au), peaks are observed at energies 79.6 [keV] and 81.0 [keV] before and after the K absorption edge energy 80.7 [keV] of gold (Au). Barium 133 and ytterbium 169 having peaks at 63.1 [keV] and 93.6 [keV] can be used as the radiation source. In this case, the reference voltage is set in the comparator 24 so as to count photons of each energy, and gold (Au) is used as described above by using the count value between the reference voltages counted by the scaler 26. ) Distribution can be visualized.
[0044]
【The invention's effect】
According to the present invention, by identifying photon energy on the detector side, it is possible to construct a CT apparatus having a new function of visualizing component analysis and distribution thereof. Further, the number of photons excluding low-energy multiple scattered photons can be counted from a signal based on the charge generated in the semiconductor element without using a physical filter. As a result, beam hardening does not occur and an image free from artifacts can be reconstructed. In addition, a three-dimensional image for each component inside the subject can also be generated from the image generated in the same manner.
[Brief description of the drawings]
FIG. 1 is a perspective view of a CT apparatus according to a first embodiment.
FIG. 2 is a perspective view for explaining a detector.
FIG. 3 is a block diagram showing a configuration of a pulse counting IC.
FIG. 4 is a diagram for explaining signal processing in a detector;
FIG. 5 is a perspective view of a CT apparatus according to a second embodiment.
FIG. 6 is a diagram illustrating a K absorption end.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... CT apparatus, 3 ... Radiation source, 5 ... Turntable, 10 ... Detector, 12 ... Semiconductor element, 16 ... Pulse counting IC, 31 ... Computer

Claims (4)

Radiation irradiating means for irradiating radiation;
Arranged in a direction perpendicular to the axial direction of the predetermined central axis passing through the measurement space and the irradiation direction of the radiation passing through the predetermined central axis while being arranged to face the radiation irradiating means across the measurement space A plurality of semiconductor elements, a signal generating means for outputting a signal corresponding to the energy of the incident photons each time a photon included in the radiation enters each of the plurality of semiconductor elements, and a plurality of predetermined threshold values Detecting means having counting means for counting the number of the signals having a wave height in a range set based on each of the plurality of semiconductor elements;
A rotation unit that changes a relative angle between the subject placed in the measurement space, the detection unit, and the radiation irradiation unit at a predetermined angle about the predetermined central axis;
Computation means for reconstructing a tomographic image of the subject based on the count value counted by the counting means,
The radiation irradiating means irradiates, as the radiation, X-rays having a continuous spectrum or a plurality of monochromatic energy radiations each having different energy,
The analyte includes at least first and second substances having different densities and / or elements,
The counting means has a wave height between two predetermined thresholds that are predetermined to selectively detect photons of the first energy included in the radiation among the plurality of predetermined thresholds. The number of signals is different from the two predetermined threshold values among the plurality of predetermined threshold values, and two predetermined energy photons are detected so as to be selectively detected. At least counting the number of the signals having a wave height between the predetermined threshold values for each of the plurality of semiconductor elements;
The CT apparatus, wherein the first energy and the second energy are different from each other. Radiation irradiating means for irradiating radiation;
A plurality of semiconductor elements arranged opposite to the radiation irradiating means across a measurement space and arranged in a direction parallel to an axial direction of a predetermined central axis penetrating the measurement space, and each of the plurality of semiconductor elements Each time a photon contained in the radiation is incident, a signal generating means for outputting a signal corresponding to the energy of the incident photon, and a signal having a wave height in a range set based on a plurality of predetermined thresholds . Detecting means having counting means for counting the number for each of the plurality of semiconductor elements;
A rotation unit that changes a relative angle between the subject placed in the measurement space, the detection unit, and the radiation irradiation unit at a predetermined angle about the predetermined central axis;
A circle including the position where the detection means is arranged around the predetermined central axis each time the relative angle between the subject, the detection means and the radiation irradiation means changes by the rotation means. Scanning means for scanning the detection means in a tangential direction at the position of the detection means on the circumference;
Computation means for reconstructing a three-dimensional image of the subject based on the count value counted by the counting means,
The radiation irradiating means irradiates, as the radiation, X-rays having a continuous spectrum or a plurality of monochromatic energy radiations each having different energy,
The analyte includes at least first and second substances having different densities and / or elements,
The counting means has a wave height between two predetermined thresholds that are predetermined to selectively detect photons of the first energy included in the radiation among the plurality of predetermined thresholds. The number of signals is different from the two predetermined threshold values among the plurality of predetermined threshold values, and two predetermined energy photons are detected so as to be selectively detected. At least counting the number of the signals having a wave height between the predetermined threshold values for each of the plurality of semiconductor elements;
The CT apparatus, wherein the first energy and the second energy are different from each other. When the radiation irradiating means irradiates a plurality of monochromatic energy radiation having different energy,
The counting means calculates the number of signals having a wave height between the predetermined threshold values set in accordance with the energy of the plurality of monochromatic energy radiations among the signals output by the signal generating means, Counting between each said threshold,
The CT apparatus according to claim 1, wherein the calculation unit reconstructs a plurality of images based on a count value for each of the threshold values counted by the counting unit. The CT apparatus according to claim 1, wherein the semiconductor element includes CdTe, CdZnTe, HgI ₂ , PbI ₂ , or GaAs.

Images