JP7066375B2 - Radiation imaging device - Google Patents

Description

The present invention relates to a radiation imaging device equipped with a photon counting type detector, and relates to a technique for suppressing shadows generated by a collimator for removing scattered radiation.

In recent years, various organizations have been developing a photon counting CT (Computed Tomography) device equipped with a detector (photon counting type detector) that employs a photon counting method. Unlike the charge integration type detector used in the conventional CT device, the photon counting type detector can individually count the radiation photons incident on the semiconductor layer which is the detection element. By counting the individual radiation photons, the energy of each radiation photon can be measured, and there is a feature that more information can be obtained as compared with the conventional CT device.

The semiconductor layer of the photon counting type detector is composed of zinc telluride (CZT), cadmium telluride (CdTe), or the like, and the semiconductor layer generates an electric charge corresponding to the energy of each incident photon. The charge is read out by a photon counting circuit connected to an electrode formed on the semiconductor layer.

In a CT device equipped with such a photon counting type detector, a collimator is arranged on the radiation incident side of the semiconductor layer in order to improve the image quality. The collimator has two main roles. The first is to prevent radiation photons from entering the boundaries of a plurality of pixels configured in the semiconductor layer and suppress crosstalk between pixels. The second is to suppress the scattered rays generated by the subject or the like from entering the semiconductor layer.

Collimators are needed to improve image quality, but they can cause other problems if the focus, which is the point of radiation, shifts. In the CT device, the focal point moves due to centrifugal force caused by the rotation of the scanner including the detector, thermal expansion of the X-ray tube, and the like. When the focal point moves, a part of the radiation originally incident on the detection surface is blocked by the collimator, and the sensitivity of the pixel changes. As a result, there is a problem that artifacts (false images) occur in the reconstructed tomographic image.

In order to suppress a change in pixel sensitivity, Patent Document 1 discloses a collimator composed of a stalk portion (stem portion) and a base portion (base portion) wider than the stalk portion. According to this collimator, the shadow of the stem portion that changes due to the movement of the focal point is stored on the base portion, so that the change in the sensitivity of the pixel is suppressed.

US Pat. No. 9,601,223

However, in the collimator disclosed in Patent Document 1, although the shadow of the stem portion that changes due to the movement of the focal point can be stored on the pedestal, the shadow generated by the pedestal causes an unnecessarily large dead zone in the semiconductor layer. It ends up. When the dead zone becomes large, a part of the radiation radiated to the subject is not used for creating a tomographic image, which leads to an increase in so-called ineffective exposure.

Therefore, the present invention provides a radiation imaging apparatus capable of suppressing an increase in the area of the dead zone of the semiconductor layer while suppressing a change in pixel sensitivity even when the focal point moves relative to the radiation detector. The purpose is.

In order to achieve the above object, the present invention is a collimator having a base portion and a stem portion, the base portion is arranged at the boundary of the pixels of the radiation detector, and the stem portion is in the direction in which the focal point moves. It is characterized in that it is arranged at a position shifted from the boundary.

More specifically, the present invention comprises a radiation source, a radiation detector that detects radiation emitted from the focal point of the radiation source, and a collimeter arranged between the radiation source and the radiation detector. The collimeter has a pedestal and a stem portion that is arranged closer to the radiation source than the pedestal and has a width narrower than the width of the pedestal. The portion is arranged at the boundary of the pixels of the radiation detector, and the stem portion is arranged at a position shifted from the boundary in the first direction in which the focus moves relative to the radiation detector. It is characterized by that.

According to the present invention, there is provided a radiation imaging apparatus capable of suppressing an increase in the area of a dead zone of a semiconductor layer while suppressing a change in pixel sensitivity even when the focus moves relative to a radiation detector. be able to.

It is a figure which shows the whole structure of the X-ray CT apparatus to which this invention is applied. It is a figure explaining the deflection caused by the rotation of a scanner. It is a figure which shows the conventional collimator shape. It is a figure which shows an example of the collimator shape of 1st Embodiment. It is a figure which shows another example of the collimator shape of 1st Embodiment. It is a figure which shows the relationship between the collimator and the semiconductor layer which concerns on 1st Embodiment. It is a figure explaining the tilt shooting. It is a figure which shows the relationship of the collimator which concerns on 2nd Embodiment, a semiconductor layer, and a mounting part. It is a figure which shows the relationship between the collimator, the semiconductor layer, and the attachment part which concerns on the modification of 2nd Embodiment. It is a figure which shows the relationship between the collimator, the semiconductor layer, and the reinforcing part which concerns on the modification of 2nd Embodiment. It is a figure which shows the state of alignment of the collimator and the semiconductor layer which concerns on 3rd Embodiment, the position in the body axis direction in each state, and the sensitivity of a pixel. It is a flowchart which shows the position adjustment method of the collimator and the semiconductor layer which concerns on 3rd Embodiment. It is a figure which shows the focal position and the sensitivity of a pixel which concerns on 3rd Embodiment. It is a flowchart which shows the position adjustment method of the detection element module which concerns on 3rd Embodiment. It is a figure which shows the relationship between the rotation speed of the scanner which concerns on 4th Embodiment, and the width of a collimator base part. It is a figure which shows the shape of the collimator which concerns on 5th Embodiment. It is a figure which shows the relationship between the collimator, the semiconductor layer, and the attachment part which concerns on 5th Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The radiation image pickup apparatus of the present invention is applied to an apparatus including a radiation source and a photon counting type detector, but in the present embodiment, as an example, the radiation is an X-ray and the radiation image pickup apparatus is an X-ray CT apparatus. The case will be described.

As shown in FIG. 1, the X-ray CT apparatus of the present embodiment has an X-ray source 100 for irradiating X-rays, an X-ray detector 101 for two-dimensionally arranging a plurality of detection elements for detecting X-rays, and a detection device. It includes a signal processing unit 102 that performs processing such as correction on the detection signal by the element and controls the device, and an image generation unit 103 that generates an image of the subject 106 using the corrected signal. The X-ray source 100 and the X-ray detector 101 are fixed to the turntable 104 at opposite positions, and are configured to rotate relatively around the subject 106 laid on the bed 105. It is also referred to as a scanner 110 including an X-ray source 100, an X-ray detector 101, and a turntable 104.

The X-ray detector 101 is composed of detection element modules 107 arranged in an arc shape centered on the X-ray source 100. The incident direction of the X-ray is the vertical direction (Y) of the paper surface, the channel direction is the horizontal direction (X) of the paper surface, and the body axis direction is the vertical direction (Z) of the paper surface. The detection element module 107 is a photon counting type detector, and includes a semiconductor layer 109 that outputs a charge corresponding to an incident X-ray photon, a collimator 108, and a photon counting circuit (not shown). The collimator 108 reduces crosstalk between pixels configured in the semiconductor layer and scattered rays generated by the subject 106 and the like. The photon counting circuit counts the electric charge output by the semiconductor layer 109 and outputs a counting signal. The semiconductor layer 109 is the same as the conventional semiconductor layer, and is composed of a semiconductor layer such as zinc telluride (CZT) or cadmium telluride (CdTe). The specific configuration of the collimator and its mounting portion will be described later.

The imaging operation of the X-ray CT device having such a configuration is the same as that of the conventional X-ray CT device, and the X-ray source 100 and the X-ray detector 101 are arranged to face each other and rotate around the subject 106. While irradiating X-rays from the X-ray source 100, the X-ray detector 101 detects the X-rays that have passed through the subject 106. The counting signal output by the photon counting circuit of the X-ray detector 101 is subjected to processing such as correction as necessary in the signal processing unit 102, and then a tomographic image (CT image) of the subject is obtained by the image generation unit 103. Generate.

Here, the X-ray CT apparatus has a plurality of imaging modes such as a state in which the scanner 110 is stationary or a state in which the scanner 110 is rotated at a predetermined speed. Further, there are cases where a plurality of rotation speeds are used properly in the same device. When the scanner 110 is rotating, centrifugal force is applied to the load of the scanner 110 due to the rotation, and the X-ray source 100 and the X-ray detector 101 bend in the direction of the arrow shown in FIG. 2, so that the X-ray detector 101 bends in the direction of the body axis. Relative focus shift occurs. Then, the X-ray incident angle to the detection element module 107 changes due to such focus movement. The collimator 108 has a function of suppressing a change in the sensitivity of the semiconductor layer while suppressing the generation of a dead zone for the semiconductor layer in response to the change in the X-ray incident angle.

Hereinafter, the conventional structure of the collimator 108 will be described in detail with reference to FIG. FIG. 3 is a cross-sectional view showing the relationship between the collimator 108 constituting the detection element module 107, the semiconductor layer 109, the focal point 206 in which the scanner 110 is stationary, and the focal point 207 in which the scanner 110 is rotating. The incident direction of the X-ray is the vertical direction (Y) of the paper surface, the body axis direction is the horizontal direction (Z) of the paper surface, and the channel direction is the vertical direction (X) of the paper surface. The collimator 108 composed of the stem portion 205 and the base portion 204 is arranged between the semiconductor layer 109 and the focal points 206 and 207. A plurality of pixels are formed in the semiconductor layer 109 by the boundary 203 of the pixels. Here, in order to obtain stable image quality in the CT apparatus, it is important that the area of the sensitive band of the semiconductor layer 109 is constant even if the focal point moves due to the rotation of the scanner 110 or the like. For that purpose, the shadow generated by the collimator 108 on the semiconductor layer 109 needs to be constant. In the conventional example, the stem portion 205 of the collimator 108 is arranged directly above the boundary 203 of the pixels. The height of the stem portion 205 is H, and the width is W. Further, the Y component of the distance between the semiconductor layer 109 side end portion of the stem portion 205 and the focal points 206 and 207 is F. The focal point 206 in which the scanner 110 is stationary is located directly above the stem 205, while the focal point 207 in which the scanner 110 is rotating moves in the apparent position in the body axis direction, and the moving distance from the focal point 206 to the focal point 207. Is E. At this time, the width B1 of the base portion 204 is determined from the range in which the shadow cast by the stem portion 205 on the base portion 204 moves due to the movement of the focal point.
B1 = 2 × H × (W / 2 + E) / (F—H) + W
= (2EH + FW) / (FH) ... (Equation 1)
Will be. The base portion 204 is arranged symmetrically directly above the boundary 203 of the pixels in order to make the crosstalk such as charge sharing that occurs between the pixels symmetrical. As a result, the base portion 204 causes a dead zone 201 in the semiconductor layer 109, and the sensitive zone becomes 200 and 202. The Z-direction width of the dead zone 201 is S1, and the Z-direction width of the sensitive bands 200 and 202 is D1. If the focal size and the height of the base in the Y direction are ignored, it can be approximated as S1≈B1. The X-ray utilization efficiency expressed as the ratio occupied by the sensitive band is D1 / (D1 + S1). Here, considering again that the rotation of the scanner 110 causes the focus movement, the movement direction of the focus is one direction from the stationary focus 206 to the rotating focus 207. Therefore, it can be said that the width originally required for the base portion 204 is N in consideration of the focus movement on only one side, and the difference U from B1 is unnecessary. A collimator having a conventional structure reduces the X-ray utilization efficiency by this width U. To solve this problem, for example, the amount of focal movement due to the rotation of the scanner 110 is grasped in advance, and the focal point and the arrangement of the detection element module are adjusted so that the moving distance of the focal point is symmetrical in the body axis direction (Z direction). That is, by adjusting the midpoint between the focal point 206 and the focal point 207 so as to be directly above the boundary 203 of the pixels, it is possible to eliminate the unnecessary width U. However, such a method is not desirable because it increases the cost of design, verification, manufacturing, and the like.

Based on the above, next, a specific embodiment of the present application of the collimator will be described.

<First Embodiment>
FIG. 4 is a cross-sectional view showing the relationship between the collimator 108, the semiconductor layer 109, the focal point 306 in which the scanner 110 is stationary, and the focal point 307 in which the scanner 110 is rotating, as in FIG. The incident direction (Y), body axis direction (Z), and channel direction (X) of X-rays are the same as those in FIG. A plurality of pixels are formed in the semiconductor layer 109 by the boundary 303 of the pixels. The collimator 108 is arranged between the semiconductor layer 109 and the focal points 306 and 307. The height of the stem portion 305 is H, and the width is W. Further, the Y component at the distance between the semiconductor layer 109 side end of the stem portion 305 and the focal points 306 and 307 is F. Here, in the present embodiment, first, the minimum required width B2 of the base portion 304 is calculated from the movement range of the shadow of the stem portion 305 as follows.
B2 = (W / 2 + E) / (F—H) × H + W + W / 2 / (F—H) × H
= (EH + FW) / (FH) ... (Equation 2)
At this time, B2 <B1 from (Equation 1) and (Equation 2), and the width of the base portion 304 in the present embodiment is smaller than the width of the base portion 204 in the prior art.

Next, the positions of the stem portion 305 and the base portion 304 in the body axis direction are determined so that the movement range of the shadow of the stem portion 305 caused by the focal movement is within the width B2 of the base portion 304 obtained in (Equation 2). .. In the case of this embodiment, the base 304 is (2EH + FW): FW ... (Equation 3).
Place the stem 305 at a position to separate into. Since the base portion 304 is arranged at the boundary 303 of the pixels, the stem portion 305 is arranged at a position shifted from the boundary 303.

The base portion 304 creates a dead zone 301 in the semiconductor layer 109, and the sensitive bands are 300 and 302. The Z-direction width of the dead zone 301 is S2, and the Z-direction width of the sensitive zones 300 and 302 is D2. If the focal size and the height of the base in the Y direction are ignored, it can be approximated as S2≈B2. Is D2 / (D2 + S2).

The cross-sectional shape of the base is not limited to the rectangle as shown in FIG. For example, by making the cross-sectional shape of the trapezoid a trapezoid whose side on the semiconductor layer side is longer than that on the focal side, it is possible to suppress fluctuations in shadows formed by the trapezoid. As a result, the change in sensitivity of the detection element due to the movement of the focal point is further suppressed, and a good image can be obtained. The trapezoidal portion having a trapezoidal cross-sectional shape will be described with reference to FIG.

FIG. 5 is a cross-sectional view showing the relationship between the collimator 108, the semiconductor layer 109, the focal point 506 in which the scanner 110 is stationary, and the focal point 507 in which the scanner 110 is rotating, as in FIG. The incident direction (Y), body axis direction (Z), and channel direction (X) of X-rays are the same as in FIG. A plurality of pixels are formed in the semiconductor layer 109 by the pixel boundaries 503. The collimator 108 is arranged between the semiconductor layer 109 and the focal points 506 and 507. The height of the stem portion 505 is H, and the width is W. Further, the Y component at the distance between the semiconductor layer 109 side end portion of the stem portion 505 and the focal points 506 and 507 is F. At this time, the minimum required width B3 of the focal side side of the base portion 504 coincides with B2. Further, the position of the stem portion 505 with respect to the base portion 504 is the same as that in FIG. Here, in FIG. 5, the cross-sectional shape of the base portion 504 is trapezoidal, and the taper ratio T between the side on the focal side and the side on the semiconductor layer side is determined from the positional relationship between the collimator and the focal point as shown in (Equation 4). ..
T = (W / 2 + E) / (F—H)… (Equation 4)
In the base portion 504 having the taper ratio T obtained by (Equation 4), the upper surface end portion of the stem portion 505 and the focal point 507 are located on the extension line of the hypotenuse. As a result, the movement of the shadow generated by the base portion 504 can be suppressed even with respect to the focal point 507 while the scanner 110 is rotating. At this time, in order to make the crosstalk between the sensitive zones 500 and 502 symmetrical, it is desirable that the taper ratios of both hypotenuses of the base portion 504 have the same value, that is, the base portion 504 has a symmetrical shape.

Next, with reference to FIG. 6, the relationship between the plurality of pixels provided in the semiconductor layer and the arrangement of the plurality of stems and pedestals provided in the collimator will be described. FIG. 6 is a YY cross-sectional view of the detection element module 107 in which the collimator 108 of the present embodiment is arranged with respect to the semiconductor layer 109. Pixel boundaries 413 to 417 are formed on the semiconductor layer 109, and pedestals 418 to 424 having the width calculated by (Equation 2) are symmetrically arranged directly above each boundary. The stalks 425 to 431 of the collimator are respectively arranged at predetermined positions on each pedestal calculated using (Equation 3). At this time, the arrangement of the stem portion in the collimator 108 shifts as a whole in the moving direction of the focal point. The sensitive band of the semiconductor layer 109 is 400 to 405, and the dead band is 406 to 412.

The stalk and pedestal having the shape determined by the above procedure have the function of keeping the shadow of the stalk in the pedestal with respect to the movement of the focal point, and have the effect of suppressing the decrease in X-ray utilization efficiency due to the width of the pedestal. There is. Further, since a heavy metal such as tungsten, molybdenum, or tantalum suitable for shielding radiation is used for the collimator, the material cost and the weight can be reduced by reducing the volume of the base.

Although the focal size and the manufacturing error of the collimator are not taken into consideration in the calculation of the collimator dimensions described above, they may be taken into consideration as necessary. Further, if the stem portion and the base portion are formed at the same time by using a means such as a 3D printer, there is an advantage that an error in the relative position can be suppressed. On the other hand, creating the stem and base separately has the advantage that the position of the stem can be adjusted after assembling the detection element module, and the stem and base are made of different materials to reduce costs and improve rigidity. There are merits that can be realized.

<Second embodiment>
In the first embodiment, it has been described that the stem of the collimator is shifted and arranged in the moving direction of the focal point. Since heavy metals are used for the collimator, if a plurality of stems are arranged in a shifted manner as a whole, the center of gravity of the collimator will be biased. In so-called tilt imaging in which the scanner is tilted in the YZ plane for imaging, it is desirable that the center of gravity of the structure in the scanner is near the center with respect to the body axis direction Z. Therefore, in the present embodiment, it will be described that the deviation of the center of gravity of the collimator caused by the arrangement of the stem portion at the shifted position is corrected.

FIG. 7 is a cross-sectional view for explaining tilt photography. The tilt shooting is a shooting performed in a state where the scanner 110 is tilted in the direction of the arrow in FIG. 7, and is used when shooting a head or the like. When performing tilt photography, it is desirable that the center of gravity of the structure in the scanner 110 is near the center with respect to the body axis direction Z.

FIG. 8 is a cross-sectional view showing the entire structure including the reinforcing portion and the mounting portion of the collimator. The collimator 108 includes an array portion 602 in which an opening, a stem portion and a base portion are repeatedly arranged, reinforcing portions 601 and 603, and mounting portions 600 and 604. The mounting portions 600 and 604 are for fixing the collimator 108 to the support portion (not shown). Further, the reinforcing portions 601 and 603 are for supplementing the strength of the array portion 602.

Since the stem portion of the array portion 602 of the present embodiment is arranged so as to shift in the moving direction of the focal point, the center of gravity of the array portion 602 is located on the moving direction side of the focal point with respect to the center of the detection element module 107. Therefore, the mounting portion 604 in the moving direction of the focal point is made smaller in the Z direction than the mounting portion 600 on the opposite side, or the mounting portion 600 is made larger in the Z direction than the mounting portion 604. By doing so, the center of gravity of the entire mounting portion is set to be opposite to the moving direction of the focal point from the center of the detection element module 107, and the center of gravity of the entire collimator 108 is aligned with the center of the detection element module 107. That is, when the Z coordinate of the center of the detection element module 107 is Z = 0, the Z coordinate of the center of gravity of the array portion 602 is Z _ARRAY , the mass of the array portion 602 is _WARRAY , and the entire mounting portion (mounting portion 600 and mounting). Assuming that the Z coordinate of the center of gravity of the part 604) is Z _MOUNT and the mass of the entire mounting part is W _MOUNT , it is assumed.
Z _ARRAY × W _ARRAY = Z _MOUNT × W _MOUNT … (Equation 5)
Set Z _MOUNT and W _MOUNT so as to be.

By aligning the center of gravity of the entire collimator 108 with the center of the detection element module 107 in this way, tilt photography with the scanner 110 can be facilitated. Further, since the center of gravity is located at the center of the structure, the weight balance can be easily adjusted.

In the present embodiment, the entire collimator is made of the same material, and the weight balance is adjusted by partially changing the shape. However, the same balance adjustment is performed by partially changing the material constituting the collimator. You may go.

Further, in the example shown in FIG. 8, the sizes of the mounting portion 600 and the mounting portion 604 are changed in the Z direction, but the sizes may be changed in the Y direction and the X direction. An example of changing the size in the X direction will be described with reference to FIG.

FIG. 9A is a cross-sectional view taken along the line XX showing the entire structure including the reinforcing portion and the mounting portion of the collimator. The collimator 108 includes an array portion 802 in which an opening, a stem portion and a base portion are repeatedly arranged, reinforcing portions 801 and 803, and mounting portions 800 and 804. The mounting portions 800 and 804 are for fixing the collimator 108 to the support portion (not shown). Further, the reinforcing portions 801 and 803 are for supplementing the strength of the array portion 802.

FIG. 9B is a cross-sectional view taken along the line AA'of the array unit 802. Pixel boundaries 806 are set for the semiconductor layer 805, the width of the collimator base 807 (light gray part) is determined using (Equation 2), and the collimator stem 808 (dark gray part) base. The mounting position with respect to 807 is determined using (Equation 3). In FIG. 9, the mounting portion 804 is made smaller in the X direction than the mounting portion 800, or the mounting portion 800 is set in response to the bias of the center of gravity of the collimator 108 due to the stem portion 808 being shifted and arranged in the moving direction of the focal point. It may be larger in the X direction than the mounting portion 804. By doing so, the center of gravity of the entire mounting portion is set to be opposite to the moving direction of the focal point from the center of the detection element module 107, and the center of gravity of the entire collimator 108 is aligned with the center of the detection element module 107. More specifically, the sizes of the mounting portion 800 and the mounting portion 804 are set so as to satisfy (Equation 5).

Further, the size of the reinforcing portion may be changed in order to adjust the center of gravity of the entire collimator 108. An example of changing the size of the reinforcing portion will be described with reference to FIG.

FIG. 10 is a cross-sectional view taken along the line YZ showing the entire structure including the reinforcing portion and the mounting portion of the collimator, as in FIG. The collimator 108 includes an array portion 902 in which an opening, a stem portion and a base portion are repeatedly arranged, reinforcing portions 901 and 903, and mounting portions 900 and 904. The mounting portions 900 and 904 are for fixing the collimator 108 to the support portion (not shown). Further, the reinforcing portions 901 and 903 are for supplementing the strength of the array portion 902.

Similar to the examples of FIGS. 8 and 9, since the stem portion of the array portion 902 is arranged so as to shift in the moving direction of the focal point, the center of gravity of the array portion 902 is located in the moving direction of the focal point rather than the center of the detection element module 107. Located on the side. Therefore, the reinforcing portion 903 in the moving direction of the focal point is made smaller in the Z direction than the reinforcing portion 901 on the opposite side, or the reinforcing portion 901 is made larger in the Z direction than the reinforcing portion 903. By doing so, the center of gravity of the entire reinforcing portion is set to be opposite to the moving direction of the focal point from the center of the detection element module 107, and the center of gravity of the entire collimator 108 is aligned with the center of the detection element module 107. That is, when the Z coordinate of the center of the detection element module 107 is Z = 0, the Z coordinate of the center of gravity of the array portion 902 is Z _ARRAY , the mass of the array portion 902 is _WARRAY , and the entire reinforcing portion (reinforcing portion 901 and reinforcement). Assuming that the Z coordinate of the center of gravity of part 903) is Z _SUPPORT and the mass of the entire reinforcing part is W _SUPPORT ,
Z _ARRAY x W _ARRAY = Z _SUPPORT x W _SUPPORT ... (Equation 6)
Z _SUPPORT and W _SUPPORT are set so as to be.

By aligning the center of gravity of the entire collimator 108 with the center of the detection element module 107 in this way, tilt imaging of the scanner 110 can be facilitated.

<Third embodiment>
In the first embodiment, it has been described that the stem of the collimator is shifted and arranged in the moving direction of the focal point. It is desirable that the detection element module provided with such a collimator be adjusted to an appropriate position with respect to the focal point. Therefore, in this embodiment, a method of adjusting the position of the detection element module will be described. There are two steps in the position adjustment method of the detection element module. In the first stage, the position of the collimator and the semiconductor layer is adjusted to complete the detection element module, and in the second stage, the focus and the detection element module are adjusted in position.

Hereinafter, as in the first embodiment, the first step will be described with reference to FIGS. 11 and 12, and the second step will be described with reference to FIGS. 13 and 14, using the radiation detector of the X-ray CT device as an example. This embodiment can be applied to all the above-described embodiments, and any of the configurations and methods described in the second embodiment may be adopted as the method of weight balancing the collimator.

The relationship between the position of the collimator and the semiconductor layer and the position in the body axis direction and the sensitivity of the pixel in each state will be described with reference to FIG. FIG. 11 (a) shows a state in which the position between the collimator 108 and the semiconductor layer 109 is correct, FIG. 11 (b) shows a state in which the position between the collimator 108 and the semiconductor layer 109 is incorrect, and FIG. 11 (c) shows the state in each state. It is a graph which showed the relationship between the body axis direction position and the sensitivity of a pixel.

When the position between the collimator 108 and the semiconductor layer 109 is correct, the sensitivity equal to or higher than the threshold value I _TARG is ensured so that no artifact occurs in the entire body axis direction position. On the other hand, when the position between the collimator 108 and the semiconductor layer 109 is incorrect, the sensitivity equal to or higher than the threshold value I _TARG is ensured in the central portion of the body axis direction position, but the pixels of the semiconductor layer 109 and the opening of the collimator 108 are secured in other regions. The positional relationship with the unit shifts, and the sensitivity becomes less than the threshold value I _TARG .

Next, a procedure for adjusting the relative position between the collimator and the semiconductor layer will be described with reference to FIG. First, as a measurement preparation (S1200), one or more detection element modules are attached at positions facing the X-ray source. Next, with the scanner 110 stationary, the detection element module is irradiated with X-rays (S1201), and the sensitivity (I) of the attached detection element module is measured (S1202). At this time, it is confirmed whether the sensitivity measured by the static scan is equal to or higher than the threshold value I _TARG in the entire body axis direction position (S1203), and if it is equal to or higher than the threshold value, it is determined that the position between the collimator 108 and the semiconductor layer 109 is correct. The position adjustment is completed (S1204). On the other hand, when a part of the sensitivity is less than the threshold value I _TARG , the position is adjusted between the collimator 108 and the semiconductor layer 109 (S1205), and the process returns to S1201. The sensitivity threshold value I _TRAG may be a uniform value for all pixels, or may be a value appropriately determined according to the position of the pixel and the position of the detection element module. Further, a value appropriately determined according to the tube voltage and tube current of the X-ray may be used.

By the above procedure, the collimator and the semiconductor layer can be adjusted to appropriate positions, and each detection element module can be completed as the first step.

FIG. 13 is a graph showing the relationship between the focal position in the Z direction and the sensitivity of the pixel when the detection element module completed through the first step is mounted at an ideal position with respect to the focal point. Assuming that the focal position when the scanner 110 is stationary is Z _STA and the focal position when the scanner 110 is rotating is Z _ROT , the moving range of the focal point is Z _STA to Z _ROT . In the range where the Z coordinate is smaller than Z _STA or larger than Z _ROT , the shadow of the stem does not fit on the base, and the sensitivity of the pixel drops sharply. On the other hand, in the range of Z _STA to Z _ROT , the sensitivity of the pixel is kept substantially constant, and the sensitivity equal to or higher than the threshold value I _TARG for preventing the occurrence of artifacts is secured.

Next, a procedure for adjusting the relative position between the collimator and the semiconductor layer will be described with reference to FIG. First, as a measurement preparation (S1400), one or more detection element modules are attached at positions facing the X-ray source. Next, with the scanner 110 stationary, the detection element module is irradiated with X-rays (S1401), and the sensitivity ( _ISTA ) of the attached detection element module is measured (S1402). Further, this time, the detection element module is irradiated with X-rays while the scanner 110 is rotated (S1403), and the sensitivity ( _IROT ) of the attached detection element module is measured (S1404). At this time, if a plurality of rotation speeds can be set, the fastest rotation speed is selected in order to create a situation in which the moving distance of the focal point is maximized. Check if the sensitivity measured by each of the static scan and the rotary scan is equal to or higher than the target value I _TARG (S1405), and if the target value is satisfied, it is judged that the collimator is properly installed and the position adjustment is completed. Becomes (S1406). On the other hand, when any of the sensitivities becomes equal to or less than the target value I _TARG , the position of the detection element module and the like are appropriately adjusted (S1407), and the process returns to S1401. The target sensitivity value I _TRAG may be a uniform value for all pixels, or may be a value appropriately determined according to the position of the pixel and the position of the detection element module. Further, a value appropriately determined according to the tube voltage and tube current of the X-ray may be used.

By the above procedure, the detection element module can be adjusted to an appropriate position with respect to the focal point. Further, the position of the detection element module is adjusted based on the sensitivity measured at the time of static scan and the sensitivity measured at the time of the fastest scan in which the fastest rotation speed is selected, without adjusting the position for each rotation speed. Therefore, the man-hours related to the position adjustment can be reduced.

<Fourth Embodiment>
In the first embodiment, the structure for suppressing the influence of the change in the shadow of the collimator due to the movement of the focal point has been described. Since the moving distance of the focal point depends on the rotation speed of the scanner, in the present embodiment, a method of setting the dimensions of the stem portion and the base portion according to the rotation speed of the scanner will be described.

Hereinafter, as in the first embodiment, the present embodiment will be described with reference to FIG. 15, using the radiation detector of the X-ray CT device as an example. This embodiment can be applied to all the above-described embodiments, and any of the configurations and methods described in each embodiment may be adopted for the method of weight balancing of the collimator.

FIG. 15 is a diagram showing the relationship between the width (B) required for the base of the collimator and the rotation speed (R) of the scanner. The relationship between the width (B) of the base and the rotation speed (R) may not actually be a quadratic function, but it has a slight fluctuation amount as long as the sensitivity change does not cause an artifact. However, in FIG. 15, the relationship between the two is simply expressed as a quadratic function.

The moving distance of the focal point has a positive correlation with the rotation speed (R) of the scanner 110, and the faster the rotating speed, the larger the moving distance of the focal point. ) Also increases. Here, the CT apparatus has a plurality of lineups, from a popular machine having a low rotation speed at the time of the fastest scanning of the scanner 110 to a high-class machine having a high rotation speed at the time of the fastest scanning. Therefore, by setting an appropriate width of the base of the collimator according to the rotation speed at the time of the fastest scan, it is possible to maximize the X-ray utilization efficiency in each CT device.

Here, the relationship between the tilt angle at the time of tilt shooting and the required width (B) of the base of the collimator will be described. When the scanner 110 is not tilted, the directions of the gravity applied to the detection element module and the centrifugal force due to rotation match and the resultant force becomes the maximum, so that the moving distance of the focal point becomes the maximum. On the other hand, when the scanner 110 is tilted, the directions of gravity and centrifugal force do not match, the resultant force becomes small, and the moving distance of the focal point also becomes small. The larger the tilt angle, the larger the angle between gravity and centrifugal force, and the smaller the resultant force between gravity and centrifugal force, so the moving distance of the focal point also becomes smaller. That is, there is a negative correlation between the tilt angle of the scanner 110 and the width (B) required for the base of the collimator.

If you have a lineup of CT devices with different rotation speeds at the fastest scan, you can configure the stem and base of the collimator separately and combine them when assembling the detection element module so that the collimators can be connected between CT devices with different rotation speeds. There is a merit that the stem can be shared.

<Fifth Embodiment>
In the first embodiment, attention is paid to the focus movement caused by the rotation of the scanner. Focus movement is also caused by changing the focus size. The direction of focus movement when changing the focus size is the channel direction. In this embodiment, a method of suppressing a change in sensitivity with respect to focus movement when the focus size is changed will be described.

Hereinafter, as in the first embodiment, the present embodiment will be described with reference to FIG. 16 by taking the radiation detector of the X-ray CT device as an example. This embodiment can be applied in parallel to all the embodiments described above.

FIG. 16A is a diagram in which the width of the base portion is further expanded in the channel direction with respect to the collimator shown in FIG. 9A. Immediately above the pixel boundary 1300 of the semiconductor layer 1303, a collimator base 1302 whose width is expanded in the channel direction is arranged. Further, the stem portion 1301 of the collimator is arranged so as to shift from the boundary 1300 in the + X direction, which is the moving direction of the focal point when the focal point size is changed. By forming the collimator in such a shape, it is possible to suppress a change in pixel sensitivity due to a focus movement in the + X direction that occurs when the focus size is changed.

16 (b) is shown in the cross-sectional view taken along the line AA'of FIG. 16 (a). The width of the base 1302 in the channel direction is calculated using (Equation 2) corresponding to the moving distance of the focal point when the focal point size is changed. Further, the position of the stem portion 1301 in the channel direction is calculated using (Equation 3). Since the moving distance of the focal point is generally smaller in the X direction than in the Z direction, the protrusion width of the base portion 1302 with respect to the stem portion 1301 is smaller in the _X direction (SX) than in the Z direction (S _Z ). ..

Next, a method of correcting the bias of the center of gravity of the collimator caused by the structure of the collimator described with reference to FIG. 16 will be described with reference to FIG. FIG. 17 is a cross-sectional view showing the entire structure including the reinforcing portion and the mounting portion of the collimator. The collimator 108 includes an array portion 1402 in which an opening, a stem portion, and a base portion are repeatedly arranged, a reinforcing portion 1401, 1403, and a mounting portion 1400, 1404. The mounting portions 1400 and 1404 are for fixing the collimator 108 to the support portion (not shown). Further, the reinforcing portions 1401 and 1403 are for supplementing the strength of the array portion 1402.

The array unit 1402 of the present embodiment is arranged so that the stem portion is shifted not only in the direction of focus movement due to rotation of the scanner 110 (-Z direction) but also in the direction of focus movement due to change in focus size (+ X direction). Therefore, the center of gravity of the array unit 1402 is located on the lower right side in FIG. 17 with respect to the center of the detection element module. Therefore, the mounting portion 1404 is made smaller than the mounting portion 1400 on the opposite side, or the mounting portion 1400 is made larger than the mounting portion 1404, and the mounting portion 1400 is shifted to the left in FIG. Align the center of gravity of the detector with the center of the detector module. That is, in addition to (Equation 6), when the X coordinate of the center of the detection element module is X = 0, the X coordinate of the center of gravity of the array unit 1402 is X _ARRAY , the mass of the array unit 1402 is _WARRAY , and the entire mounting unit is used. Assuming that the X coordinate of the center of gravity of (mounting part 1400 and mounting part 1404) is X _MOUNT and the total mass of the entire mounting part is W _MOUNT , it is assumed.
X _ARRAY × W _ARRAY = X _MOUNT × W _MOUNT … (Equation 7)
Set X _MOUNT and W _MOUNT so that

By aligning the center of gravity of the entire collimator 108 with the center of the detection element module in this way, the weight balance of the scanner 110 can be easily adjusted.

Although the position of the mounting portion 1400 is changed in FIG. 17 for adjusting the weight balance in the X direction, the position of the mounting portion 1404 and the dimensions and positions of the reinforcing portions 1401 and 1403 may be changed. Further, in the present embodiment, the entire collimator is made of the same material, and the weight balance is adjusted by partially changing the shape, but the same balance adjustment is performed by partially changing the material constituting the collimator. You may go.

100: X-ray source, 101: X-ray detector, 102: Signal processing unit, 103: Image generation unit, 104: Turntable, 105: Sleeper unit, 106: Subject, 107: Detection element module, 108: Collimeter, 109 : Semiconductor layer, 110: Scanner, 200: Sensitive band, 201: Insensitive band, 202: Sensitive band, 203: Pixel boundary, 204: Base, 205: Stem, 206: Static focus, 207: Rotation Medium focus, 300: sensitive band, 301: dead zone, 302: sensitive band, 303: pixel boundary, 304: base, 305: stem, 306: stationary focus, 307: rotating focus, 500: Sensitive zone, 501: Insensitive zone, 502: Sensitive zone, 503: Pixel boundary, 504: Base, 505: Stem, 506: Static focus, 507: Rotating focus, 400-405: Sensitive band, 406 to 412: Insensitive band, 413 to 417: Pixel boundary, 418 to 424: Base part, 425 to 431: Stem part, 600: Mounting part, 601: Reinforcement part, 602: Array part, 603: Reinforcement Part, 604: Mounting part, 800: Mounting part, 801: Reinforcing part, 802: Array part, 803: Reinforcing part, 804: Mounting part, 805: Semiconductor layer, 806: Pixel boundary, 807: Base part, 808: Stem part, 900: Mounting part, 901: Reinforcing part, 902: Array part, 903: Reinforcing part, 904: Mounting part, 1300: Pixel boundary, 1301: Stem part, 1302: Base part, 1303: Semiconductor layer, 1400 : Mounting part, 1401: Reinforcing part, 1402: Array part, 1403: Reinforcing part, 1404: Mounting part

Claims (20)

A radiation image pickup device comprising a radiation source, a radiation detector for detecting radiation emitted from the focal point of the radiation source, and a collimeter arranged between the radiation source and the radiation detector.
The collimator has a pedestal and a stem that is located closer to the radiation source than the pedestal and has a width narrower than the width of the pedestal.
The pedestal is arranged at the boundary between the pixels of the radiation detector.
The stem portion is arranged at a position shifted from the boundary to the side in the first direction parallel to the detection surface of the radiation detector in the direction in which the focal point moves relative to the radiation detector. A radiation imaging device characterized by this. The radiation imaging apparatus according to claim 1.
The width of the pedestal in the first direction and the position where the stem is arranged are the moving distance of the focal point, the height of the stem and the width in the first direction, and the stem from the focal point. A radiation imaging device characterized in that it is calculated based on the distance to a part. The radiation imaging device according to claim 2.
The width B of the pedestal in the first direction is E for the moving distance of the focal point, H for the height of the stalk, F for the distance from the focal point to the pedestal, and the first direction of the stalk. When the width of is W
B = (EH + FW) / (FH)
A radiation imaging device characterized by being calculated by. The radiation imaging apparatus according to claim 3.
The position where the stem portion is arranged is such that the base portion is (2EH + FW): FW in the first direction.
A radiation imaging device characterized by being in a position to be separated into. The radiation imaging apparatus according to claim 1.
A radiation imaging device characterized in that the cross-sectional shape of the pedestal is a trapezoid in which the side on the radiation detector side is longer than the side on the focal side. The radiation imaging apparatus according to claim 5.
The taper ratio between the focal side side of the trapezoid and the radiation detector side is the moving distance of the focal point, the height of the stem portion, and the distance from the focal point to the pedestal portion. A radiation imaging device characterized in that it is calculated based on the width of the stem portion in the first direction. The radiation imaging apparatus according to claim 6.
The taper ratio T is when the height of the stem portion is H, the distance from the focal point to the pedestal portion is F, and the width of the stem portion in the first direction is W.
T = (E + W / 2) / (FH)
A radiation imaging device characterized by being calculated by. The radiation imaging apparatus according to claim 5.
A radiation imaging device characterized in that the trapezoid has a symmetrical shape. The radiation imaging apparatus according to claim 1.
A radiation imaging device having a structure that corrects the deviation of the center of gravity of the collimator caused by the arrangement of the stem portion at a shifted position to a predetermined position. The radiation imaging apparatus according to claim 9.
A radiation imaging device characterized in that the predetermined position is the center of the radiation detector in the first direction. The radiation imaging apparatus according to claim 9.
A radiation imaging device characterized in that the deviation of the center of gravity of the collimator is corrected by a mounting portion. The radiation imaging apparatus according to claim 9.
A radiation imaging device characterized in that the bias of the center of gravity of the collimator is corrected by a reinforcing portion. The radiation imaging apparatus according to claim 1.
A radiation imaging device characterized in that the position of the radiation detector with respect to the collimator is set based on the sensitivity of the radiation detector over the entire position of the position in the first direction. The radiation imaging apparatus according to claim 13.
A radiation imaging device characterized in that the position of the radiation detector with respect to the focal point is set based on the sensitivity measured during a static scan and the sensitivity measured during the fastest scan. The radiation imaging apparatus according to claim 14.
A radiation imaging device characterized in that the width of the base portion is set wider as the rotation speed at the time of the fastest scan increases. The radiation imaging apparatus according to claim 1.
When the focal point moves in the second direction, which is orthogonal to the first direction and also orthogonal to the radiation radiation direction, the stem portion is arranged at a position shifted from the boundary to the second direction. A radiation imaging device characterized by the above. The radiation imaging apparatus according to claim 16.
A radiation imaging apparatus characterized in that the protrusion width in the first direction with respect to the stem portion of the pedestal portion is larger than the protrusion width in the second direction. The radiation imaging apparatus according to claim 16.
The width of the pedestal portion in the second direction and the position where the stem portion is shifted and arranged in the second direction are the moving distance of the focal point in the second direction and the height of the stem portion. A radiation imaging device characterized by being calculated based on the width in the second direction and the distance from the focal point to the stem portion. The radiation imaging apparatus according to claim 1.
A radiation imaging device characterized in that the stem portion and the pedestal portion are configured as separate parts. The radiation imaging apparatus according to claim 19.
A radiation imaging device characterized in that the stem portion and the pedestal portion are made of different materials.

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