JP2007130232A - Radiation imaging device - Google Patents

Abstract

A radiation imaging apparatus capable of suppressing an increase in noise for a radiation detection signal with a small time delay included in the radiation detection signal while removing a large time delay included in the radiation detection signal. For the purpose.
When a time delay included in an X-ray detection signal for X-ray image acquisition taken out from an FPD 2 at a predetermined sampling time interval Δt is removed by recursive calculation processing by a time delay removal unit 10, removal adjustment is performed. The unit 11 is configured to make an adjustment to increase the degree of removal of the time delay only when the time delay is large than when the time delay is small. Therefore, when the time delay included in the radiation detection signal is small while the large time delay included in the radiation detection signal is removed, the degree of time delay being removed by the time delay removal unit 10 is weak and noise is reduced. The increase can be suppressed.
[Selection] Figure 1

Description

  The present invention provides medical or industrial use in which a radiation detection signal for acquiring a radiation image is taken out from a radiation detection means at a predetermined sampling time interval from a radiation detection means in accordance with radiation irradiation to a subject to be imaged by the radiation irradiation means. In particular, the present invention relates to a technique for removing the time delay of the radiation detection signal caused by the radiation detection means from the radiation detection signal extracted from the radiation detection means.

  As an X-ray detector for detecting a transmitted X-ray image of a subject that has recently been generated in association with X-ray irradiation by an X-ray tube in a medical X-ray fluoroscopic apparatus, which is one of the representative devices of a radiation imaging apparatus. A flat panel X-ray detector (hereinafter referred to as “FPD” where appropriate) in which an extremely large number of X-ray detection elements using X-ray sensitive semiconductors are arranged vertically and horizontally on an X-ray detection surface is used. Yes.

  That is, in the X-ray fluoroscopic apparatus, the subject is based on the X-ray detection signal for one X-ray image taken out from the FPD at a predetermined sampling time interval with the X-ray irradiation to the subject by the X-ray tube. X-ray images corresponding to the transmitted X-ray images are acquired at predetermined sampling time intervals. The FPD is lighter than a conventionally used image intensifier or the like, and does not generate complicated detection distortion, so that it is advantageous in terms of apparatus structure and detection signal processing.

  However, when the FPD is used, for example, when panning (that is, when the imaging position is moved), a part of the X-rays irradiated from the X-ray tube does not pass through the subject and directly enters the FPD. An X-ray with a high signal intensity is detected, and an X-ray detection signal with a higher signal intensity is output. In the X-ray image based on the X-ray detection signal output from the FPD, a white and strong shadow remains. Here, there is a relationship that the greater the intensity of the X-ray detection signal, the greater the time delay of the X-ray detection signal output from the FPD. Therefore, when the sampling time interval for extracting the X-ray detection signal from the FPD is short, the remainder of the signal that cannot be extracted is added to the next X-ray detection signal as a time delay. Therefore, for example, when an X-ray detection signal for one image is taken out from the FPD at a sampling time interval of 30 times per second to acquire an X-ray image and display a moving image, the time delay is an afterimage of the previous X-ray image. As a result of appearing and causing the image double phenomenon, the moving image is blurred.

  Therefore, in the conventional apparatus, recursive calculation processing for uniformly removing the time delay is performed on all X-ray detection signals output from the FPD, and the X-ray detection signals subjected to this recursive calculation processing are subjected to recursive calculation processing. The X-ray image based on this is acquired, and the time delay part is prevented from appearing as an afterimage (refer patent document 1).

JP 2004-24741 A (pages 6 to 8, FIGS. 1 and 7 to 9)

  However, the conventional X-ray fluoroscopic apparatus has the following problems. In other words, in order to remove a large time delay included in a part of the X-ray detection signals, recursive calculation processing for uniformly removing the time delay is performed on all X-ray detection signals. As a result, noise increases in all X-ray detection signals, and the image quality of the X-ray image decreases. That is, in the X-ray detection signal related to the region of interest of the X-ray image, the intensity of the X-ray detection signal is usually not large, and it is not necessary to remove the time delay, so that the time delay can be removed. There is a problem in that recursive calculation processing is performed, noise increases due to this processing, and image quality in the region of interest deteriorates.

  The present invention has been made in view of such circumstances, and removes a large time delay included in the radiation detection signal from the radiation detection signal extracted from the radiation detection means such as the FPD. An object of the present invention is to provide a radiation imaging apparatus that can suppress an increase in noise for a radiation detection signal with a small time delay included in the detection signal.

In order to achieve such an object, the present invention has the following configuration.
That is, a radiation imaging apparatus according to the invention of claim 1 includes: (A) a radiation irradiating unit that irradiates a subject to be imaged; (B) a radiation detecting unit that detects radiation transmitted through the subject; C) signal sampling means for extracting a radiation detection signal for acquiring a radiation image corresponding to the transmitted radiation image of the subject from the radiation detection means at a predetermined sampling time interval; and (D) a predetermined sampling time interval by the signal sampling means. A time delay removing means for removing the time delay included in the radiation detection signal taken out from the radiation detection signal by recursive calculation processing; and (E) time delay removal by recursive calculation processing by the time delay removal means. When the time delay is large, the removal adjustment is performed to increase the degree of removal of the time delay compared to when the time delay is small. And it is characterized in that it comprises a means.

  [Operation / Effect] According to the apparatus of the first aspect of the present invention, a radiological image is output that is output from the radiation detection means at a predetermined sampling time interval when the subject to be imaged is irradiated by the radiation irradiation means. The time delay included in the radiation detection signal for use is removed by a recursive calculation process by the time delay removal means. However, when removing the time delay by recursive calculation processing, the removal adjustment means performs an adjustment to increase the degree of removing the time delay when the time delay is large, compared to when the time delay is small. In the case of the apparatus according to the first aspect of the present invention, a radiation image is acquired in accordance with the radiation detection signal from which the time delay has been removed by the recursive arithmetic processing by the time delay removal means.

As described above, the apparatus according to the first aspect of the invention includes a time included in a radiation detection signal for acquiring a radiological image output at a predetermined sampling time interval from the radiation detection means in accordance with radiation irradiation to the subject to be imaged. When removing the delay by recursive calculation processing, a configuration is provided in which the degree of removal of the time delay is adjusted more strongly when the time delay is large than when the time delay is small. Further, there is a correlation that the noise of the radiation detection signal applied with the recursive calculation processing increases as the degree of removal of the time delay becomes stronger.
Therefore, in the case of the apparatus according to the first aspect of the present invention, when the time delay included in the radiation detection signal for acquiring the radiographic image is removed by recursive calculation processing, when the time delay is large, the time delay is small. The degree of time delay removal is stronger than that, so that the time delay included in the radiation detection signal is small while the time delay included in the radiation detection signal is small. The degree of removal of the delay is weak, and the increase in noise can be suppressed.

According to a second aspect of the present invention, in the radiation imaging apparatus according to the first aspect, the time delay removing means performs recursive calculation processing for removing the time delay from the radiation detection signal according to the following equation A: ,
X (n) = [1 / (k / u)] I (n)-{([1- (k / u)] / (k / u)} I (n-1) .. A
However,
X (n): Radiation detection signal after removal of the time delay at the nth sampling time (radiation detection signal before the time delay occurs)
I (n): Radiation detection signal extracted at the nth sampling time point I (n-1): Radiation detection signal extracted at the (n-1) th sampling time point k: Parameter that defines the degree of time delay (0 <k <1 range)
u: a parameter for adjusting the degree of removal of the time delay (k <u <1 range)
The adjustment of the degree of removal of the time delay by the removal adjusting means is performed by radiation detection using a radiation detection signal I (n-1) or a radiation detection signal close in time to the radiation detection signal I (n-1). This is performed by changing the parameter u in the expression A based on the magnitude of the signal intensity.

  [Operation / Effect] In the case of the invention of claim 2, the radiation detection signal from which the time delay has been removed is quickly obtained by the simple expression of Expression A. Further, based on the magnitude of the intensity of the radiation detection signal using the radiation detection signal I (n−1) or the radiation detection signal temporally close to the radiation detection signal I (n−1), Since it can be performed by changing the parameter u in the inside, the adjustment of the removal degree for the time delay by the removal adjusting means can be made with high accuracy corresponding to the magnitude of the intensity of the radiation detection signal. In addition, since the radiation detection signal I (n-1) or a radiation detection signal that is close in time to the radiation detection signal I (n-1) can be used, the degree of removal of the time delay by the removal adjustment means In this adjustment, the accuracy and processing of the adjustment are examined, and an optimal radiation detection signal can be used, and the removal degree for the time delay can be variously adjusted.

According to a third aspect of the present invention, in the radiation imaging apparatus according to the first aspect, the time delay removing means performs recursive calculation processing for removing the time delay from the radiation detection signal according to the following equation A: ,
X (n) = [1 / (k / u)] I (n)-{([1- (k / u)] / (k / u)} I (n-1) .. A
However,
X (n): Radiation detection signal after removal of the time delay at the nth sampling time (radiation detection signal before the time delay occurs)
I (n): Radiation detection signal extracted at the nth sampling time point I (n-1): Radiation detection signal extracted at the (n-1) th sampling time point k: Parameter that defines the degree of time delay (0 <k <1 range)
u: a parameter for adjusting the degree of removal of the time delay (k <u <1 range)
The adjustment of the removal degree for the time delay by the removal adjusting means is performed when the parameter u in the equation A is set when the average intensity of all the radiation detection signals extracted before the radiation detection signal I (n) is large. This is done by making the radiation detection signal larger than when the average intensity is small.

  [Operation / Effect] In the case of the invention of claim 3, the radiation detection signal from which the time delay is removed is quickly obtained by the simple expression of Expression A. In addition, there is a correlation that the time delay of the radiation detection signal increases as the average intensity (signal intensity) of all the radiation detection signals extracted before the radiation detection signal I (n) increases. The removal adjustment means by increasing the parameter u in the case where the average intensity of all the radiation detection signals extracted before the radiation detection signal I (n) is larger than when the average intensity of the radiation detection signals is small. The degree of removal of the time delay due to can be easily adjusted. Further, since the adjustment of the degree of removal of the time delay uses the average intensity of all the radiation detection signals extracted before the radiation detection signal I (n), one of the acquired total radiation detection signals. Even if it is abnormal due to some problem, the parameter u can be obtained from the average of all the radiation detection signals and can be highly accurate.

  According to a fourth aspect of the present invention, in the radiation imaging apparatus according to the second aspect of the present invention, the adjustment of the degree of removal of the time delay by the removal adjustment means is performed by setting the parameter u in the expression A to the radiation detection signal I. This is performed by increasing the intensity of the radiation detection signal I (n-1) when the intensity of (n-1) is large than when the intensity of the radiation detection signal I (n-1) is small.

  [Operation / Effect] In the case of the invention of claim 4, since there is a correlation that the time delay of the radiation detection signal increases as the intensity (signal intensity) of the radiation detection signal I (n-1) increases. The parameter u is set to be larger when the intensity of the radiation detection signal I (n-1) is larger than when the intensity of the radiation detection signal I (n-1) is small. The removal degree can be easily adjusted. Further, the adjustment of the degree of removal of the time delay is performed using the radiation detection signal sampled immediately before the nth sampling ((n−1) th), and the nth and (n−1) th. Since the radiation detection signals are approximated, it is possible to perform highly accurate adjustment.

  According to a fifth aspect of the present invention, in the radiation imaging apparatus according to any one of the second to fourth aspects, a parameter sudden change suppression that suppresses a rapid change in the parameter u accompanying a sudden intensity change in the radiation detection signal. Means are provided.

[Operation / Effect] In the case of the invention of claim 3, the rapid change of the parameter u in the expression A accompanying the rapid intensity change of the radiation detection signal is often caused by an undesirable image change in the radiation image. However, since the rapid change of the parameter u in the equation A due to the rapid change in the intensity of the radiation detection signal is suppressed by the parameter sudden change suppression means, an undesirable image change due to the rapid change of the parameter u is caused by the radiation image. Can be avoided.

  In the case of the radiation imaging apparatus of the present invention, the time delay included in the radiation detection signal for acquiring a radiological image output at a predetermined sampling time interval from the radiation detection means in accordance with the radiation irradiation to the subject to be imaged is recursed. When the time delay is large, the adjustment is made so that the degree of removal of the time delay is stronger when the time delay is large than when the time delay is small. On the other hand, there is a correlation that the noise of the radiation detection signal applied with the recursive calculation processing increases as the degree of time delay removal increases.

Therefore, in the radiation imaging apparatus of the present invention, when removing the time delay included in the radiation detection signal for acquiring the radiation image by recursive calculation processing, only when the time delay is large than when the time delay is small. Since the degree of removal of the time delay is strengthened, it is possible to suppress an increase in noise of the radiation detection signal accompanying the recursive calculation process except when the time delay is large.
Therefore, according to the radiation imaging apparatus of the present invention, it is possible to remove the time delay of the radiation detection signal caused by the radiation detection means from the radiation detection signal extracted from the radiation detection means such as the FPD while suppressing increase in noise. it can.

  Embodiments of the radiation imaging apparatus of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an overall configuration of a medical X-ray fluoroscopic apparatus according to the embodiment, and FIG. 2 is a flat panel X-ray detector (radiation detection means) used in the X-ray fluoroscopic apparatus of the embodiment. FIG. 3 is a schematic view showing an X-ray image acquisition situation by the X-ray fluoroscopic apparatus of the embodiment.

  The X-ray fluoroscopic apparatus of FIG. 1 includes an X-ray tube (radiation irradiating means) 1 that irradiates a subject M to be radiographed with X-rays, and a flat panel X-ray detection that detects X-rays transmitted through the subject M. And an X-ray detection signal (radiation detection signal) for acquiring an X-ray image corresponding to the transmitted X-ray image of the subject M from the FPD 2 is converted into a digital signal and subjected to predetermined sampling. The detection data collecting unit (signal sampling means) 3 taken out at the time interval Δt and the X-ray detection signal (described later in detail) taken out by the detection data collecting unit 3 are subjected to necessary signal processing and output as an X-ray image. A detection signal processing unit 4 and an image monitor 5 for displaying an X-ray image output from the detection signal processing unit 4 are provided.

In the case of the apparatus of the embodiment, during X-ray imaging, an X-ray detection signal for X-ray image acquisition is sent from the FPD 2 to the detection data collection unit 3 in accordance with the X-ray irradiation to the subject M by the X-ray tube 1. Are extracted at the sampling time interval Δt, and necessary signal processing is performed by the detection signal processing unit 4, and an X-ray image is output and displayed on the image monitor 5 at a predetermined sampling time interval Δt. For example, if the sampling time interval Δt is (1/30) seconds, 30 X-ray images are displayed one after another on the image monitor 5 and so-called moving image display is performed.
Hereinafter, the configuration of each part of the X-ray fluoroscopic apparatus according to the embodiment will be described in detail.

  The X-ray tube 1 and the FPD 2 are arranged to face each other with the subject M interposed therebetween, and the X-ray tube 1 is subjected to the control of the X-ray irradiation control unit 6 during X-ray imaging, and the subject M has a cone-beam X shape. At the same time as irradiating the X-ray, a transmission X-ray image of the subject M generated by the X-ray irradiation is arranged on the X-ray detection surface of the FPD 2. An irradiation condition such as an X-ray irradiation dose is input by an operator through the operation unit 7 or the like, and the X-ray irradiation control unit 6 controls the X-ray tube 1 according to the input irradiation condition. For example, the X-ray irradiation dose irradiated from the X-ray tube 1 in the case of continuous fluoroscopic irradiation and single X-ray imaging irradiation is the X-ray irradiation dose in the single X-ray imaging irradiation. The control is increased. The image monitor 5 displays an operation menu necessary for execution of X-ray imaging, and performs operations such as setting conditions and command input related to X-ray imaging by the operation unit 7 and the like according to the displayed operation menu. It is.

As shown in FIG. 2, the FPD 2 has a large number of X-ray detection elements 2a along the body axis direction X and body side direction Y of the subject M on the X-ray detection surface onto which the transmitted X-ray image of the subject M is projected. The configuration is arranged vertically and horizontally. For example, the X-ray detection elements 2a are arranged vertically and horizontally in a matrix of about 1000 to 2000 × 1000 to 2000 on the X-ray detection surface having a width of about 30 cm × 30 cm. Each X-ray detection element 2a of the FPD 2 has a corresponding relationship with each pixel of the X-ray image acquired by the detection signal processing unit 4, and the detection signal processing unit 4 performs X-rays based on the X-ray detection signal extracted from the FPD 2. An X-ray image corresponding to the transmitted X-ray image projected on the detection surface is obtained.
The FPD 2 provided in the apparatus of the embodiment is a direct conversion type X-ray detector that directly converts incident X-rays into carriers. However, after the FPD 2 converts incident X-rays into light once, the carrier further It may be an indirect conversion type X-ray detector that converts to X.

The detection data collecting unit 3 includes a current / voltage conversion amplifier (not shown), a multiplexer (not shown), an A / D converter (not shown), and the like, and X-rays for each X-ray image. The detection signals are continuously taken out at the sampling time interval Δt and output to the detection signal processing unit 4 at the subsequent stage.
That is, all the X-ray detection signals for the transmitted X-ray image at that time are collected at the sampling time interval Δt and output to the detection signal processing unit 4, and as shown in FIG. Line images P (1), P (2), P (3)... P (n-1), P (n)... Are successively acquired and output at predetermined sampling time intervals Δt, and image monitor 5 Is displayed on the screen.

  In the case of the apparatus of the embodiment, as shown in FIG. 1, the detection signal processing unit 4 stores a first detection signal memory 8 for storing the X-ray detection signal I (n) extracted at the n-th sampling time point. A second detection signal memory 9 for storing the X-ray detection signal I (n-1) taken out at the nearest (n-1) th sampling time, and a k value memory 23 for storing the parameter k Based on the X-ray detection signal I (n) and the X-ray detection signal I (n-1), the time delay included in the X-ray detection signal extracted at the sampling time interval Δt is detected by recursive calculation processing. A time delay removing unit 10 for obtaining an X-ray detection signal X (n) after removal from the signal and removing a time delay at the n-th sampling time point (no time delay), and the intensity of the X-ray detection signal Based on the magnitude, recursively by changing the parameter u in equation A And removing adjuster 11 for adjusting the removal degree of time delay caused by calculation process is deployed.

That is, the time delay removal unit 10 is configured to perform recursive calculation processing for removing the time delay from the X-ray detection signal according to the following equation A.
X (n) = [1 / (k / u)] I (n)-{([1- (k / u)] / (k / u)} I (n-1) .. A
However,
X (n): X-ray detection signal after removal of the time delay at the nth sampling time point I (n): X-ray detection signal taken out at the nth sampling time point I (n-1): (n− 1) X-ray detection signal taken out at the time of the first sampling k: parameter defining the degree of time delay (range 0 <k <1)
u: a parameter for adjusting the degree of removal of the time delay (k <u <1 range)

  The adjustment of the degree of removal of the time delay in the removal adjustment unit 11 is performed when the time delay is large when the time delay is removed by the recursive calculation process. The adjustment is made to increase the degree to which it is performed. Specifically, the parameter u in the equation A is set larger when the intensity of the X-ray detection signal I (n-1) is larger than when the intensity of the X-ray detection signal I (n-1) is small. It is set as the structure performed by.

  The parameter k is a fixed number determined by the time delay characteristic (response speed) of the FPD 2 and is a value obtained by a measurement performed in advance. The parameter u is obtained by a monotonically increasing function as shown in FIG. 4, for example, and the value of the parameter u increases monotonously as the intensity of the X-ray detection signal I (n-1) increases. is there. Note that the monotonically increasing function as shown in FIG. 4 is obtained in advance through experiments or the like.

Further, the derivation of the formula A is performed as follows. First, Expression B for obtaining a uniform time delay for all X-ray detection signals by recursive calculation processing is obtained. The X-ray detection signal I (n) taken out at the nth sampling time and the X-ray detection signal I (n-1) taken out at the (n-1) th sampling time one frame before are expressed by the following equations. Represented.
I (n) = kX (n) + k (1-k) X (n-1) + k (1-k) (1-k) X (n-2) +.
I (n-1) = kX (n-1) + k (1-k) X (n-2) + k (1-k) (1-k) X (n-3) +.
Furthermore, multiplying both sides of the formula of I (n-1) by (1-k),
(1-k) I (n-1) = k (1-k) X (n-1) + k (1-k) (1-k) X (n-2) + k (1-k) (1- k) (1-k) X (n-3) + ...
Then, subtracting this (1-k) I (n-1) equation from the equation I (n)
I (n)-(1-k) I (n-1) = kX (n)
And multiplying both sides of this equation by (1 / k),
X (n) = (1 / k) I (n)-[(1-k) / k] I (n-1)... B
It becomes.

Here, when recursive calculation processing is performed using Expression B, the quantum noise is only included in X (n) and does not increase in the recursive calculation processing. Since σ is included in both I (n) and I (n−1), it is increased by recursive computation. Here, the sum of the variance of electrical noise of I (n) and I (n-1) is obtained as follows.
(1 / k) * σ * σ + [(1−k) k] * σ * σ = [(2−k) k] * σ * σ = (2K−1) * σ * σ
However, K = 1 / k. In addition, since the variance of electrical noise is obtained as an average value obtained by squaring electrical noise, the square root of (2K−1) * σ * σ is used to return this electrical noise variance to simple electrical noise. Is obtained as √ (2K−1) * σ. That is, the electrical noise σ of the X-ray detection signal increases by √ (2K−1) times by recursive calculation processing.

  Therefore, if the recursive calculation process is performed on an X-ray detection signal that does not require a recursive calculation process, noise is unnecessarily increased. Therefore, the time delay removal is not performed with the same degree for all X-ray detection signals. In other words, when the time delay that requires recursive computation is large, the degree of time delay removal is increased, and when the time delay that does not require recursive computation is small, the time delay is removed. Decrease the degree to do. Therefore, in order to realize this, by putting the parameter u depending on the intensity (magnitude) of the X-ray detection signal I (n-1) into the expression B by dividing the parameter k of the expression B, Formula A is derived, and the parameter u in Formula A is made larger when the intensity of the X-ray detection signal I (n-1) is larger than when the intensity of the X-ray detection signal I (n-1) is small. This is the configuration that is realized.

  As shown in FIG. 5, the time delay removal unit 10 stores the X-ray detection signal I (n) read from the first detection signal memory 8 and the parameter u and k value memory 23 output from the removal adjustment unit 11. The first calculation unit 12 that performs the calculation of [1 / (k / u)] I (n) based on the parameter k and the X-ray detection signal I (n−1) read from the second detection signal memory 9. ) And the parameter u output from the removal adjusting unit 11 and the parameter k stored in the k value memory 23, ([1- (k / u)] / (k / u)) I (n− 1) and a subtracting unit 14 for subtracting the calculation result of the second calculation unit 13 from the calculation result of the first calculation unit 12, and at the n-th sampling time point from the subtraction unit 14 The X-ray detection signal X (n) after the time delay is removed is output.

  As shown in FIG. 6, the removal adjustment unit 11 converts the X-ray detection signal I (n−1) read from the second detection signal memory 9 into a parameter u according to the monotonically increasing function shown in FIG. And a recursive filter (parameter abrupt change suppression means) 16 that suppresses a sudden change in the parameter u accompanying a sudden change in the intensity of the X-ray detection signal I (n-1).

  The rapid change of the parameter u in the expression A accompanying the rapid intensity change of the X-ray detection signal I (n-1) often causes an undesirable image change in the X-ray image. 16 suppresses an abrupt change in the parameter u in the equation A due to an abrupt intensity change in the X-ray detection signal I (n-1). It is possible to avoid the occurrence in the line image.

  The recursive filter 16 multiplies the parameter u output from the I · u converter 15 by a constant m (0 <m <1), and the parameter u one point before output from the frame memory 20. The second multiplier 18 that multiplies [1-m (0 <m <1)], the value multiplied by the first multiplier 17 and the value multiplied by the second multiplier 18 are added, and the current parameter The adder 19 is output to the frame memory 20 as u, and the frame memory 20 stores the parameter u output from the adder 19.

That is, if the current parameter u is u (n), the parameter u (n) represented by the following equation is output from the frame memory 20 to the time delay removing unit 10.
u (n) = mu (n) + m (1-m) u (n-1) + m (1-m) ² u (n-2) +.
Where m is a constant (0 <m <1)

The X-ray detection signal X (n) after the time delay removal output from the time delay removal unit 10 is adjusted to an X-ray image by the X-ray image acquisition unit 21 and output to the image monitor 5.
The main control unit 22 is mainly composed of a computer and its operation program. The main control unit 22 sends command signals and data to each unit in accordance with the progress of X-ray imaging and the content of commands from the operation unit 7. Operate normally.

  Next, the operation of removing the time delay by the recursive calculation processing in the time delay removing unit 10 based on the adjustment of the degree of removal of the time delay performed in the removal adjusting unit 11 will be described with reference to FIGS. To do. First, as shown in FIG. 5, the first arithmetic unit 12 removes the X-ray detection signal I (n) taken out at the n-th sampling time, a parameter k that defines the degree of time delay, and the removal of time delay. The parameter u for adjusting the degree is input, and the second arithmetic unit 13 defines the X-ray detection signal I (n−1) extracted at the (n−1) th sampling time and the degree of time delay. A parameter k and a parameter u for adjusting the degree of removal of the time delay are input.

Further, as shown in FIG. 4, the parameter u is a parameter that changes from k to 1 in accordance with the value (intensity) of I (n-1). When the value of I (n-1) is small, the parameter u Becomes a value close to k. Here, an expression [1 / (k / u)] I (n) indicating an operation performed by the first operation unit 12 and an expression ([1- (k / u) indicating an operation performed by the second operation unit 13 are shown. )] / (K / u)) Substituting u = k into I (n-1)
In the first calculation unit 12, [1 / (k / k)] I (n) = I (n)
In the second calculation unit 13, ([1- (k / k)] / (k / k)) I (n-1) = 0
Thus, the subtractor 14 performs processing of I (n) -0 = I (n). That is, the time delay removal unit 10 does not remove the time delay by recursive calculation processing.

When the value of I (n−1) is large, the parameter u is close to 1. Here, an expression [1 / (k / u)] I (n) indicating an operation performed by the first operation unit 12 and an expression ([1- (k / u) indicating an operation performed by the second operation unit 13 are shown. )] / (K / u)) Substituting u = 1 into I (n-1)
In the first calculation unit 12, [1 / (k / 1)] I (n) = (1 / k) I (n)
In the second calculation unit 13, ([1- (k / 1)] / (k / 1)) I (n-1) = [(1-k) / k] I (n-1)
Thus, the subtracting unit 14 performs processing of (1 / k) I (n)-[(1-k) / k] I (n-1). That is, the same processing as that shown in Expression B is performed. That is, recursive calculation processing for removing the time delay included in the X-ray detection signal is performed.

  Therefore, in the first calculation unit 12 and the second calculation unit 13 of the time delay removal unit 10, when the time delay is large, the time delay is removed based on the value of the parameter u compared to when the time delay is small. Adjustment of the removal of the time delay for increasing the degree is performed, and further, the calculation result of the second calculation unit 13 is subtracted from the calculation result of the first calculation unit 12 by the subtraction unit 14, thereby obtaining the nth sampling time point. The X-ray detection signal X (n) after removal of the time delay is output.

  As described above, in the case of the apparatus of the embodiment, X-rays for acquiring X-ray images output from the FPD 2 at a predetermined sampling time interval in accordance with the X-ray irradiation to the subject M to be imaged by the X-ray tube 1. When removing the time delay included in the detection signal by recursive calculation processing by the time delay removal unit 10, the degree of removing the time delay is larger when the time delay is large than when the time delay is small. Is configured to be performed by the removal adjusting unit 11. In addition, there is a correlation that the noise of the X-ray detection signal applied along with the recursive calculation processing increases as the degree of time delay removal increases.

  Therefore, in the apparatus of the embodiment, when the time delay included in the X-ray detection signal for X-ray image acquisition is removed by recursive calculation processing, the time delay is larger than when the time delay is small. Since the degree of removal of the time delay is strengthened, the time delay removal unit 10 uses the time delay removal unit 10 to remove the time delay included in the X-ray detection signal while removing the large time delay included in the line detection signal. The degree of removal of the delay is weak, and the increase in noise can be suppressed.

  Further, an X-ray detection signal from which the time delay is removed is quickly obtained by a simple expression of Expression A. In addition, since there is a correlation that the time delay of the X-ray detection signal increases as the intensity (signal intensity) of the X-ray detection signal I (n-1) increases, the parameter u in equation A is expressed as X-ray. When the intensity of the detection signal I (n-1) is large, the removal adjustment unit 11 can easily adjust the degree of removal of the time delay by increasing the intensity of the detection signal I (n-1) than when the intensity of the X-ray detection signal I (n-1) is small. It can be done. Further, the adjustment of the degree of removal of the time delay is performed using the radiation detection signal sampled immediately before the nth sampling ((n−1) th), and the nth and (n−1) th. Since the radiation detection signals are approximated, it is possible to perform highly accurate adjustment.

  Further, a sudden change in the parameter u in the equation A accompanying a sudden intensity change of the X-ray detection signal I (n-1) often causes an undesirable image change in the X-ray image. Since the recursive filter 16 suppresses the rapid change of the parameter u in the equation A accompanying the rapid change in the intensity of the X-ray detection signal I (n-1), an undesirable image change due to the rapid change of the parameter u. Can be avoided in the X-ray image.

The present invention is not limited to the above embodiment, and can be modified as follows.
(1) In the apparatus of the above embodiment, the adjustment of the removal degree for the time delay in the removal adjusting unit 11 is performed when the parameter u in the expression A is set to a high intensity of the X-ray detection signal I (n-1). Although the X-ray detection signal I (n-1) is made larger than when the intensity is small, the parameter u in the equation A is set to the X-ray detection signal I (n-1). When the intensity of the X-ray detection signal selected from any one of the X-ray detection signals close in time is large, the selected X-ray detection signal is made larger than when the intensity is small. It may be.

  Specifically, it demonstrates using FIGS. 7-9. FIG. 7 is a block diagram showing a detailed configuration of the detection signal processing unit of the apparatus of the modification (1). FIG. 8 is a graph showing the correlation between the parameters of the apparatus of the modification (1) and the intensity of the X-ray detection signal. FIG. 9 is a block diagram illustrating a detailed configuration of a detection signal processing unit including a third detection signal memory of the apparatus of the modification example (1). Examples of X-ray detection signals that are close in time to the X-ray detection signal I (n-1) include X-ray detection signals I (n) and I (n-2). Here, when the X-ray detection signal that is close in time to the X-ray detection signal I (n−1) is the X-ray detection signal I (n), the removal adjustment unit 11 is as shown in FIG. Further, an X-ray detection signal I (n) read from the first detection signal memory 8 is converted into a parameter u according to a monotonically increasing function shown in FIG. The recursive filter 16 suppresses the rapid change of the parameter u accompanying the rapid intensity change of (n).

  Further, when the X-ray detection signal that is close in time to the X-ray detection signal I (n−1) is the X-ray detection signal I (n−2), the removal adjustment unit 11 is shown in FIG. As shown, an X-ray detection signal I (n-2) read from the third detection signal memory 24 is converted into a parameter u according to a monotonically increasing function shown in FIG. The recursive filter 16 suppresses a sudden change in the parameter u accompanying a sudden intensity change of the line detection signal I (n-2).

  The rapid change of the parameter u in the equation A accompanying the rapid intensity change of the X-ray detection signal I (n) and the X-ray detection signal I (n-2) is often an undesired image change in the X-ray image. However, the recursive filter 16 suppresses the rapid change of the parameter u in the expression A accompanying the rapid intensity change of the X-ray detection signal I (n) and the X-ray detection signal I (n-2). Therefore, it is possible to avoid an undesirable image change caused by a sudden change in the parameter u in the X-ray image.

  Here, there is a correlation that the time delay of the X-ray detection signal increases as the intensity (signal intensity) of the X-ray detection signal close in time to the X-ray detection signal I (n−1) increases. Therefore, it is selected not only based on the intensity of the X-ray detection signal I (n-1) but also from any one of the X-ray detection signals that are temporally close to the X-ray detection signal I (n-1). For example, the parameter u in the expression A is set to the X-ray detection signal I (n-1) based on the intensities of the X-ray detection signal I (n) and the X-ray detection signal I (n-2). When the intensities of the X-ray detection signal I (n) and the X-ray detection signal I (n-2) that are close in time are high, the selected X-ray detection signal I (n) and X-ray detection signal I (n The removal adjustment unit 11 can easily adjust the removal degree of the time delay by increasing the intensity such as -2). Further, since the X-ray detection signal I (n-1) or the X-ray detection signal close in time to the X-ray detection signal I (n-1) can be used, the time delay in the removal adjusting unit 11 As the adjustment of the removal degree of the minute, the accuracy and processing of the adjustment can be studied, the optimum radiation detection signal can be used, and the removal degree of the time delay can be variously adjusted. Further, an X-ray detection signal from which the time delay is removed is quickly obtained by a simple expression of Expression A.

  (2) In the apparatus of the above embodiment, the adjustment of the removal degree for the time delay in the removal adjusting unit 11 is performed when the parameter u in the equation A is set to a high intensity of the X-ray detection signal I (n-1). The X-ray detection signal I (n-1) is made larger than when the intensity is small, but the parameter u in the equation A is extracted before the X-ray detection signal I (n). Alternatively, when the average intensity of all the X-ray detection signals is large, the average intensity of the X-ray detection signals may be set larger than when the average intensity is small.

  Specifically, description will be made with reference to FIGS. FIG. 10 is a block diagram showing a detailed configuration of the detection signal processing unit of the apparatus of the modification (2). FIG. 11 is a graph showing the correlation between the parameters of the apparatus of the modification (2) and the intensity of the X-ray detection signal. As shown in FIG. 10, the signal detection processing unit 4 detects all X-ray detection signals (I (n ()) extracted before the X-ray detection signal I (n), which is detection data collected by the detection data collection unit in the past. n-1), I (n-2), I (n-3),...)) and all X-ray detection signal memories 25 stored in this X-ray detection signal memory 25 Based on the average intensity of the X-ray detection signals calculated by the average intensity calculator 26 for calculating the average intensity of the X-ray detection signals and the average intensity of all the X-ray detection signals calculated by the average intensity calculator 26, the parameter u I / u conversion section 15 for converting to X, and recursive filter 16 for suppressing a rapid change in parameter u accompanying a rapid intensity change in X-ray detection signal I (n).

  A sudden change in the parameter u in the equation A accompanying a sudden change in the average intensity of all the X-ray detection signals often causes an undesirable image change in the X-ray image, but the recursive filter 16 This suppresses the rapid change of the parameter u in the equation A accompanying the sudden change in the average intensity of all the X-ray detection signals, so that an undesired image change due to the rapid change of the parameter u is caused by the X-ray image. Can be avoided.

  Here, there is a correlation that the time delay of the X-ray detection signal increases as the average intensity (signal intensity) of all the X-ray detection signals extracted before the X-ray detection signal I (n) increases. Therefore, not only based on the intensity of the X-ray detection signal I (n-1), but also based on the average intensity of all X-ray detection signals taken before the X-ray detection signal I (n), The parameter u is removed by increasing the average intensity of all X-ray detection signals extracted before the X-ray detection signal I (n) than when the average intensity of the X-ray detection signals is small. Adjustment of the degree of time delay removal by the adjustment unit 11 can be easily performed. Further, an X-ray detection signal from which the time delay is removed is quickly obtained by a simple expression of Expression A. The adjustment of the degree of removal of the time delay uses the average intensity of all X-ray detection signals extracted before the X-ray detection signal I (n). Even if one of them is abnormal due to some problem, the parameter u can be obtained from the average of all the X-ray detection signals and can be highly accurate.

  (3) The apparatus of the above embodiment has a configuration in which the time delay removal unit 10 performs recursive calculation processing according to Formula A, but the time delay removal unit 10 performs recursive calculation processing according to a formula other than Formula A. It may be what you do.

  (4) In the case of the apparatus of the above embodiment, the relationship between the parameter u and the intensity of the X-ray detection signal I (n-1) is as shown in FIG. The strength relationship of -1) is not limited to that shown in FIG.

  (5) In the apparatus of the above embodiment, the X-ray is detected by the FPD 2. However, the present invention is applied to an apparatus using an X-ray detector that causes a time delay of X-ray detection signals other than the FPD. Is also applicable.

  (6) Although the apparatus of the above embodiment is an X-ray fluoroscopic apparatus, the present invention can be applied to devices other than the X-ray fluoroscopic apparatus such as an X-ray CT apparatus.

  (7) The apparatus of the above embodiment is a medical apparatus, but the present invention is not limited to medical use but can be applied to industrial apparatuses such as non-destructive inspection equipment.

  (8) Although the apparatus of the said Example was an apparatus which uses X-rays as a radiation, this invention is applicable not only to an X-ray but the apparatus which uses radiations other than an X-ray.

  It should be noted that the adjustment of the degree of removal of the time delay by the removal adjusting means according to claim 2 is performed in time with respect to the radiation detection signal I (n-1) or the radiation detection signal I (n-1). “Using a near radiation detection signal” means that the adjustment of the degree of removal of the time delay by the removal adjustment unit 11 is performed on the radiation detection signal I (n−1) or the radiation detection signal I (n−1). A value or an average value selected from any one of the radiation detection signals that are close in time may be used. In addition, the radiation detection signal I (n-1) or the radiation detection signal I may be used. The scope of right is also included in the case of using a value indicating that the time delay is large from the radiation detection signal close in time to (n-1).

It is a block diagram which shows the whole structure of the X-ray fluoroscopic imaging apparatus of an Example. It is a top view which shows the basic composition of FPD used for the apparatus of an Example. It is a schematic diagram which shows the acquisition condition of the X-ray image by the apparatus of an Example. It is a graph which shows the correlation with the parameter in the apparatus of an Example, and the intensity | strength of a X-ray detection signal. It is a block diagram which shows the detailed structure of the time delay removal part of the apparatus of an Example. It is a block diagram which shows the detailed structure of the removal adjustment part of the apparatus of an Example. It is a block diagram which shows the detailed structure of the detection signal process part of the apparatus of a modification (1). It is a graph which shows the correlation of the parameter of the apparatus of a modification (1), and the intensity | strength of a X-ray detection signal. It is a block diagram which shows the detailed structure of the detection signal process part provided with the 3rd detection signal memory of the apparatus of the modification (1). It is a block diagram which shows the detailed structure of the detection signal process part of the apparatus of a modification (2). It is a graph which shows the correlation of the parameter of the apparatus of a modification (2), and the intensity | strength of a X-ray detection signal.

Explanation of symbols

1 X-ray tube (radiation irradiation means)
2 ... FPD (radiation detection means)
3 ... Detection data collection unit (signal sampling means)
10: Time delay removal unit (time delay removal means)
11: Removal adjustment unit (removal adjustment means)
16 ... Recursive filter (parameter sudden change suppression means)
I (n) ... X-ray (radiation) detection signal extracted at the nth sampling time point I (n-1) ... X-ray (radiation) detection signal extracted at the (n-1) th sampling time point k ... Parameter that defines the degree of time delay M ... Subject u ... Parameter that adjusts the degree of removal of time delay X (n) ... X-ray (radiation) detection signal Δt after removal of time delay at the n-th sampling time … Predetermined sampling time interval

Claims (5)

  (A) radiation irradiating means for irradiating a subject to be imaged; (B) radiation detecting means for detecting radiation transmitted through the subject; and (C) a transmitted radiation image of the subject from the radiation detecting means. A signal sampling means for taking out a corresponding radiation detection signal for acquiring a radiological image at a predetermined sampling time interval; and (D) a time delay included in the radiation detection signal taken out at a predetermined sampling time interval by the signal sampling means, A time delay removing means for removing from the radiation detection signal by recursive calculation processing; and (E) when the time delay is removed by recursive calculation processing by the time delay removing means, if the time delay is large, the time delay is A radiation imaging apparatus comprising: a removal adjustment unit that performs adjustment to increase the degree of removal of the time delay compared to a case where the time delay is smaller . The radiation imaging apparatus according to claim 1, wherein the time delay removing unit performs recursive calculation processing for removing a time delay from the radiation detection signal according to the following expression A:
X (n) = [1 / (k / u)] I (n)-{([1- (k / u)] / (k / u)} I (n-1) .. A
However,
X (n): Radiation detection signal after removal of the time delay at the nth sampling time point I (n): Radiation detection signal taken out at the nth sampling time point I (n-1): (n-1) Radiation detection signal taken out at the time of the first sampling k: parameter that defines the degree of time delay (range 0 <k <1)
u: a parameter for adjusting the degree of removal of the time delay (k <u <1 range)
The adjustment of the removal degree for the time delay by the removal adjusting means is performed by using a radiation detection signal I (n-1) or a radiation detection signal that is temporally close to the radiation detection signal I (n-1). A radiation imaging apparatus that is performed by changing the parameter u in Formula A based on the magnitude of the intensity of the detection signal. The radiation imaging apparatus according to claim 1, wherein the time delay removing unit performs recursive calculation processing for removing a time delay from the radiation detection signal according to the following expression A:
X (n) = [1 / (k / u)] I (n)-{([1- (k / u)] / (k / u)} I (n-1) .. A
However,
X (n): Radiation detection signal after removal of the time delay at the nth sampling time point I (n): Radiation detection signal taken out at the nth sampling time point I (n-1): (n-1) Radiation detection signal taken out at the time of the first sampling k: parameter that defines the degree of time delay (range 0 <k <1)
u: a parameter for adjusting the degree of removal of the time delay (k <u <1 range)
The adjustment of the degree of removal of the time delay by the removal adjustment means is performed when the average intensity of all the radiation detection signals extracted before the radiation detection signal I (n) is set to the parameter u in the equation A. A radiation imaging apparatus which is performed by making the average of all the radiation detection signals larger than when the average intensity is small.   3. The radiation imaging apparatus according to claim 2, wherein the adjustment of the degree of removal of the time delay by the removal adjusting means is performed when the intensity of the radiation detection signal I (n-1) is set to the parameter u in the equation A. A radiation imaging apparatus that performs the radiation detection by increasing the intensity of the radiation detection signal I (n-1) as compared with the case where the intensity is small. 5. The radiation imaging apparatus according to claim 2, further comprising a parameter sudden change suppression unit that suppresses a sudden change in the parameter u accompanying a sudden change in intensity of the radiation detection signal.

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