JP2007044496A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the influence of scattered radiation originating from X-rays from the X-ray tube of the other pair in an multi-tube type X-ray CT apparatus including a plurality of pairs of X-ray tubes and detectors. <P>SOLUTION: This X-ray CT apparatus is provided with the X-ray tubes 121 and 122, slit mechanisms 161 and 162, X-ray detectors 131 and 132 which form pairs with the X-ray tubes, a support mechanism 11 which supports the X-ray tubes and the X-ray detectors so as to allow them to rotate about a rotation axis parallel to the slice direction, a correction unit 221 which corrects data from each detection element located in an area which X-rays passing through the slit mechanism directly strike, by using data from at least one detection element located outside the area and associated with the same channel, and a reconstruction unit 23 which reconstructs image data on the basis of the corrected data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multi-tube type X-ray CT apparatus equipped with a plurality of pairs of X-ray tubes and detectors.

  Conventionally, an X-ray CT apparatus (computer tomography apparatus) irradiates a subject with X-rays generated by an X-ray tube, detects X-rays transmitted through the subject with an X-ray detector, and detects the detected data. A tomographic image is obtained by reconstruction processing by a computer device. In addition, two or more pairs of X-ray tubes and detectors are prepared, and a plurality of pairs of X-ray tubes and detectors are mounted on an annular rotating mount, thereby reducing the rotation angle of the mount A spherical X-ray CT apparatus is also known.

  As a multi-tube type X-ray CT apparatus, for example, there is one described in Patent Document 1, which shows an example having a therapeutic X-ray tube and a video X-ray tube. By the way, in a multi-tube type X-ray CT apparatus in which two or more pairs of X-ray tubes and detectors are mounted, a direct ray from a pair of X-ray tubes and a scattered ray from an X-ray tube other than the pair. May reach the detector, and direct and scattered rays are not very different in characteristics, so it is difficult to separate them. For this reason, the image quality of the reconstructed image is adversely affected by scattered rays from X-ray tubes other than the pair.

Conventionally, in a multi-tube X-ray CT apparatus equipped with two or more pairs of X-ray tubes and X-ray detectors, scattered rays from X-ray tubes other than the pair have an adverse effect, and the quality of the reconstructed image is low. There was a problem that it decreased.
JP 2004-73406 A

  An object of the present invention is to reduce the influence of scattered radiation derived from X-rays from the other pair of X-ray tubes in a multi-tube type X-ray CT apparatus equipped with a plurality of pairs of X-ray tubes and detectors. There is.

  In one aspect, the present invention provides a plurality of X-ray tubes, a plurality of slit mechanisms having variable slit widths respectively provided in the plurality of X-ray tubes, and a plurality of pairs constituting the plurality of X-ray tubes and a plurality of pairs. An X-ray detector, and each of the X-ray detectors includes a plurality of detection elements arrayed in a matrix with respect to a channel direction and a slice direction, the X-ray tube and the X-ray detector, In order to reduce a scattered radiation component derived from X-rays generated by an X-ray tube other than the X-ray tube constituting the pair, and a support mechanism that rotatably supports around a parallel rotation axis, the slit mechanism is A correction unit that corrects the data of each of the detection elements located in the region directly irradiated with the passed X-rays with the data of at least one detection element related to the same channel outside the region; and To provide an X-ray CT apparatus comprising a reconstruction unit which reconstructs image data based on Tadashisa data.

  According to the present invention, in a multi-tube type X-ray CT apparatus equipped with a plurality of pairs of an X-ray tube and a detector, the influence of scattered radiation derived from X-rays from the other pair of X-ray tubes is reduced. be able to.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram showing the overall configuration of an embodiment of the X-ray CT apparatus of the present invention. In FIG. 1, the X-ray CT apparatus (X-ray computed tomography apparatus) of this embodiment has a gantry 10, a computer apparatus 20, and a bed (not shown). The gantry 10 is a multi-tube type, and a plurality of pairs of an X-ray tube and an X-ray detector are mounted. In the present embodiment, the description will be made with a two-tube type.

  The gantry 10 is provided with a rotating gantry 11 and is rotated around the rotation axis R by a rotating mechanism (not shown). A direction parallel to the rotation axis R is referred to as a slice direction. A first pair of the X-ray tube 121 and the X-ray detector 131 and a second pair of the X-ray tube 122 and the X-ray detector 132 are mounted on the rotary mount 11. The first pair of imaging axes and the second pair of imaging axes typically intersect at 90 degrees. The imaging axis is a line connecting the X-ray focal point and the detector center. The central part of the rotating gantry 11 is opened, and the subject P placed on the couch top 14 is inserted therein.

  The X-ray detectors 131 and 132 are provided with collimators 151 and 152 for converging X-rays facing the X-ray tubes 121 and 122, respectively. Further, slit mechanisms 161 and 162 are disposed in the X-ray tubes 121 and 122, respectively. The slit mechanisms 161 and 162 have at least two lead slit plates. In order to adjust the width of the slit between the two slit plates, the slit plate is movably supported in parallel to the rotation axis R. The X-ray thickness is determined by the slit width.

  Outputs of the X-ray detectors 131 and 132 are sent to data collection units 171 and 172, respectively, and supplied to a preprocessing unit (described later) of the computer apparatus 20. In addition, the gantry 10 is provided with a control unit 18 for controlling the tube voltage of the X-ray tubes 121 and 122, controlling the rotation of the rotating mount 11, and the like.

  On the other hand, the computer apparatus 20 has a central control unit 21 to which a preprocessing unit 22, a reconstruction processing unit 23, an image display unit 24, an operation unit 25, and the like are connected via a data / control bus line 201. Yes. X-rays that have passed through the subject P are detected by the X-ray detectors 131 and 132, converted into electric signals, amplified by the data collection units 171 and 172, converted into digital data, and the imaging data is sent to the preprocessing unit 22. Supplied. The preprocessing unit 22 performs processing such as correction of signal intensity and correction of signal loss, and also includes a scattered radiation correction processing unit 221, and mainly scattered radiation derived from X-rays from other pairs of X-ray tubes. The image data processed by the preprocessing unit 22 is output on the bus line 201.

  The central control unit 21 controls the operation of each unit of the computer device 20 and the control unit 18 of the gantry 10. The reconstruction processing unit 23 reconstructs tomographic image data based on the projection data. The image display unit 24 includes a display that displays medical images and the like, and the operation unit 25 inputs information such as a patient's condition and examination method by a doctor.

  FIG. 2 is an enlarged view of the configuration of the X-ray tubes 121 and 122 and the detectors 131 and 132 shown in FIG. 1, and shows a first pair of the X-ray tube 121 and the X-ray detector 131, and an X-ray tube. 2 shows a configuration of a second pair of 122 and the X-ray detector 132. In FIG. 2, the first pair of the X-ray tube 121 and the X-ray detector 131 is representatively illustrated, but the second pair of the X-ray tube 122 and the X-ray detector 132 is the first pair. Since the configuration is the same except that it is shifted by 90 degrees with respect to the pair, the illustration is omitted in FIG.

  In FIG. 2, a slit 161 is disposed so as to face the X-ray tube 121, and the X-ray thickness is regulated by the slit 161. The X-ray detector 131 includes a large number of detection elements arranged in the channel direction (CH) and the slice direction (L), and detects the incident X-ray x1.

  Further, the X-ray detector 131 is provided with a metal plate collimator 151 (see FIG. 1) in the channel (CH) direction so as to receive X-rays from the paired X-ray tube directions. . Furthermore, the multi-tube type X-ray CT apparatus has a smaller rotation angle than the single-tube type, and the time required for acquiring projection data can be shortened, so that the time resolution can be improved.

  X-ray detectors 131 and 132 detect X-rays (direct rays) from a pair of X-ray tubes 121 and 122 and scattered rays from other pairs of X-ray tubes by a detection element group in the central portion L0 in the slice direction. In addition to detection, scattered radiation from other pairs of X-ray tubes is detected by the detection element group located in the regions L1 and L2 outside each row.

  FIG. 3 is an explanatory diagram for explaining the influence of scattered rays from X-ray tubes other than the pair. In the case of FIG. 3, X-rays emitted from the X-ray tube 121 are detected by the X-ray detector 131, and X-rays emitted from the X-ray tube 122 are detected by the X-ray detector 132.

  On the other hand, X-rays from the other pair of X-ray tubes 121 enter the detector 132 after being scattered on the surface of the subject P and inside p1. Similarly, X-rays from the other pair of X-ray tubes 122 are scattered on the surface of the subject P and the internal portion p1 and enter the detector 131. Scattered rays from the subject P are scattered radially and most of the scattered rays are blocked by the collimators 151 and 152, but some scattered rays (for example, d1 and d2) pass through the collimators 151 and 152 to the detectors 131 and 132. Incident. Scattered rays d1 scattered at the scattering angle α are scattered when the X-rays from the X-ray tube 121 hit the internal portion p1 of the subject P, and are scattered at a refraction angle α of about 90 degrees and enter the X-ray detector 132. To do. Scattered rays d2 are scattered when the X-rays from the X-ray tube 122 hit the internal portion p1 of the subject P, and are scattered at a refraction angle α of about 90 degrees and enter the X-ray detector 131. The X-rays generated by the other pair of X-ray tubes 122 (121) are scattered on the body surface of the subject P, and the scattered radiation that directly enters the detector 131 (132) without being attenuated has the most adverse effect. Invite

  With reference to FIG. 4, the generation state of scattered radiation will be described more specifically. FIG. 4 schematically shows a state in which X-rays from the X-ray tube 121 are scattered by the internal portion p1 of the subject and enter the other pair of X-ray detectors 132.

  The X-ray detector 132 receives X-rays x2 (direct lines) from the X-ray tube 122 constituting the pair, but X-rays from the other pair of X-ray tubes 121 hit the internal portion p1 of the subject. Then, the light is scattered at a refraction angle of angle α, and a scattered ray d1 is generated. The scattered radiation d1 spreads and scatters in the slice direction (L) of the X-ray detector 132, and enters the detector 132 with a spread of about 5 to 6 degrees as indicated by the angle β.

  Since α is sufficiently large with respect to β (α >> β), the scattered radiation d1 strikes sufficiently (uniformly) from end to end of the row of detector elements in the same channel of the detectors 131 and 132. Further, since the X-ray x1 has a predetermined slice thickness (T), it is considered that there are scattering points corresponding to the slice thickness, and the scattered dose is an integrated value for the scattering points. Therefore, even if there is a point that specifically scatters strongly in a specific direction, the specificity is reduced by integrating the scattered radiation from end to end of the detection element in the slice direction, and the scattering in the slice direction is reduced. The line intensity distribution is uniform.

  Further, only scattered rays are incident on the detection elements located at both ends of the detectors 131 and 132 in the slice direction, and direct rays from the X-ray tubes 121 and 122 are not incident. This will be described with reference to FIG. FIG. 5 is a diagram showing a state in which the scattered radiation d1 is applied to the X-ray detector 132, and is a diagram when the scattered radiation source is P1, and the X-ray detector 132 is cut in the slice direction. is there. As can be seen from FIG. 5, the central region L0 in the slice direction of the X-ray detector 132 is hit by the X-ray bundle x2 (direct line) from the X-ray tube 122 and the scattered radiation d1, but both end regions L1 in the slice direction. , L2 hits only the scattered radiation d1. Therefore, only the X-ray scattered rays can be measured by the detection elements in the regions L1 and L2.

  In this embodiment, when detecting X-rays radiated through the slits of the slit mechanisms 161 and 162 with the detectors 131 and 132, the detection elements in the end regions L1 and L2 in the slice direction are used for scattered radiation measurement. By using the fact that there is no significant difference in scattered dose between the central region L0 in the slice direction and the outer regions L1 and L2, the same channel is obtained from the X-ray measurement value by the detection element in the central portion of the same channel. The influence of scattered radiation can be reduced by subtracting the X-ray measurement values by the detection elements at both ends of the.

  That is, correction is performed by using the X-ray data detected by the detection elements in the outer regions L1 and L2 in the slice direction of the detectors 131 and 132 so as to reduce the influence of scattered radiation. This is performed by the scattered radiation correction processing unit 221 of the unit 22. The scattered ray correction processing unit 221 calculates scattered ray data by integrating the X-ray data detected by the elements in the outer regions L1 and L2 by the number of elements in the column, and detects the data in the central region L0 in the slice direction of the detectors 131 and 132. The value of the scattered radiation data is subtracted from the value of the X-ray data detected by the element, and imaging data is obtained based on the result, and is output on the bus line 201.

  FIG. 6 is a diagram for explaining the operation of the scattered radiation correction processing unit 221, where the vertical axis represents the data values at the detectors 131 and 132, and the horizontal axis represents the slice numbers of the detectors 131 and 132. From the X-ray direct line value detected in the central region L0 of the detectors 131 and 132, from the data value of each detection element in the X-ray irradiation region L0, each detection element in the regions L1 and L2 outside the X-ray irradiation region Is subtracted from the data value for the scattered radiation component.

  The width of the X-ray detectors 131 and 132 in the slice direction needs to be slightly larger than the maximum set value of the X-ray slice thickness (T) defined by the width of the slit 162. When the slit is narrowed down, the scattered radiation can be measured with high accuracy by using the regions immediately outside the central region L0 where the direct line hits in the same channel as L1 and L2 for measuring the scattered radiation.

  The scattered radiation correction according to the present embodiment will be described in more detail. As shown in FIG. 7, scan conditions are set prior to scanning. The scan condition setting support unit 22 is provided to support setting of scan conditions by the user. The scan condition setting support unit 22 provides a plurality of scan plans according to the physique of the subject, the examination site, and the like. The scan plan includes a scan mode (single / helical), a distinction between a one-tube scanning mode and a two-tube scanning mode, tube voltage, tube current, imaging slice thickness, imaging slice number, imaging FOV, and the like. In this device, one of the pairs is paused, and the 1-tube mode in which data collection (scanning) is performed using only the other pair and the 2-tube mode in which data collection is performed using two pairs are selected. Can be done.

  The slit width is determined by the combination of the photographing slice thickness and the number of photographing slices. Thereby, the X-ray irradiation area where X-rays are irradiated on the effective sensitivity areas of the detectors 131 and 132 is limited to the width of the imaging slice thickness × the number of imaging slices. In the two-tube mode, a plurality of candidates related to the combination of the imaging slice thickness and the number of imaging slices are excluded from the effective sensitivity region unique to the detectors 131 and 132 except for two rows at both ends used for collecting scattered radiation data. The area is prepared as the maximum range. On the other hand, in the single-tube mode, since the scattered radiation correction is not performed, a plurality of candidates related to the combination of the imaging slice thickness and the number of imaging slices have a maximum range of all effective sensitivity areas unique to the detectors 131 and 132. Are prepared within that range.

  The user operates the operation unit 25 to select a desired combination from a plurality of candidates related to the combination of the imaging slice thickness and the number of imaging slices provided from the scan condition setting support unit 22. In order to irradiate only the region corresponding to the combination of the selected imaging slice thickness and the number of imaging slices, the control unit 21 controls the slit mechanisms 161 and 162 to adjust the slit width. In the single tube mode, X-rays may be irradiated to the entire effective sensitivity region unique to the detectors 131 and 132.

  In the single tube mode, since the scattered radiation correction is not performed, the entire region can be irradiated with X-rays. On the other hand, in the 2-tube mode, the entire region is not irradiated with X-rays. In the two-tube mode, the maximum irradiation area is an area excluding two rows at both ends, as shown in FIG. The reason is that in the two-tube mode, the data of the detection elements on the two rows at both ends are used as data for correcting scattered radiation.

  Although FIG. 8 illustrates the 10-row type, the present embodiment can be applied to any number of rows as long as there are 4 or more rows.

  In the one-tube mode, naturally, a situation in which scattered rays derived from the X-rays of the other pair of X-ray tubes do not occur. In the one-tube mode, unnecessary reduction in the S / N ratio can be prevented by not correcting the scattered radiation.

When the user presses the scan trigger button on the operation unit 25, scanning is started.
The control unit 21 prepares different processing procedures for the 1-tube mode and the 2-tube mode. In the single-tube mode, scattered radiation correction is not performed, so in scanning S18, only the data of the detection elements in the X-ray irradiation region, that is, the projection data required for image reconstruction transmitted through the subject is acquired (pre-processing). Apply to (S19). Collecting only the projection data is typically defined as storing only the projection data and not storing data of the detection elements in the X-ray non-irradiation region outside the X-ray irradiation region.

  In the two-tube mode, in scanning S12, together with projection data (also referred to as inside data) of the detection elements in the X-ray irradiation region, detection element data (scattered rays) in the two X-ray non-irradiation regions at both ends on the outer side. Data or outside data). The outside data is subjected to preprocessing equivalent to projection data (S13). For example, in the example of FIG. 8, the detection element data D1 and D10 outside the X-ray irradiation area are outside data, and the detection element data D2-D9 in the X-ray irradiation area are inside data (projection data). is there.

  The scattered radiation correction processing unit 221 outputs inside data of each detection element located within the X-ray irradiation region to which X-rays that have passed through the slits of the slit mechanisms 161 and 162 are directly irradiated, outside the X-ray irradiation region. Therefore, the correction is performed by the outside data of the detection element related to the same channel as the correction target data (S14, S15). At the time of correction, the scattered radiation correction processing unit 221 determines a correction value corresponding to the correction mode for each channel from outside data. For convenience of explanation, as illustrated in FIG. 8, the outside data is D1, D10, and inside data D2-D9. As for channel n, each value of the inside data D2-D9 is corrected by the correction value determined from the outside data D1, D10.

  In the initially set correction mode 1), the average value of the outside data D1 and D10 at both ends is determined as the correction value.

  In the correction mode 2), one of the outside data D1 and D10 is determined as a correction value. For example, the maximum value, minimum value, or approximate value of the predetermined value of the outside data D1 and D10 is determined as the correction value of the channel n.

  In the correction mode 3), the outside data D1 of the neighboring element is assigned as a correction value for the inside data D2-D5, and the outside data D10 of the neighboring element is assigned as a correction value for the inside data D6-D9.

  In the correction mode 4), the outside data D1 of the neighboring element is assigned as the correction value for the inside data D2 and D3, the outside data D10 of the neighboring element is assigned as the correction value for the inside data D8 and D9, and the center inside data The average value of the outside data D1 and D10 is determined as a correction value for D4-D7.

  Each value of the inside data D2-D9 is corrected based on the correction value determined in S14 (S15).

  Under the control of the control unit 21, the reconstruction processing unit 23 reconstructs image data based on the inside data (projection data) corrected in S15 in the two-tube mode, and corrects in the one-tube mode. The image data is reconstructed based on the projection data that is not received (S16). The reconstructed image is displayed on the image display unit 24. The user can check the displayed image and change the correction mode as necessary (S17).

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

FIG. 1 is an overall configuration diagram illustrating an embodiment of an X-ray CT apparatus according to the present invention. FIG. 2 is a perspective view showing a configuration of a main part of the X-ray CT apparatus in the same embodiment. FIG. 3 is an explanatory diagram for explaining the influence of scattered radiation of the X-ray CT apparatus according to the embodiment. FIG. 4 is an explanatory diagram schematically explaining the generation state of scattered rays of the X-ray CT apparatus. FIG. 5 is an explanatory diagram for explaining a situation when the generation of scattered radiation of the X-ray CT apparatus is viewed in the slice direction of the X-ray detector. FIG. 6 is an explanatory diagram for explaining the operation of the scattered radiation correction processing unit in the embodiment. FIG. 7 is a flowchart showing a series of flow from scan condition setting to image reconstruction according to the present embodiment. FIG. 8 is a supplementary diagram of S15 of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Gantry, 20 ... Computer apparatus, 11 ... Rotary mount, 121, 122 ... X-ray tube, 131, 132 ... X-ray detector, 14 ... Top plate, 151, 152 ... Collimator, 161, 162 ... Slit mechanism, 171 172 ... Data collection unit 18 ... Control unit 21 ... Central control unit 22 ... Pre-processing unit 23 ... Reconstruction processing unit 24 ... Image display unit 25 ... Operation unit 201 ... Data / control bus line 221: Scattered ray correction processing unit.

Claims (9)

A plurality of X-ray tubes;
A plurality of slit mechanisms each having a variable slit width provided in each of the plurality of X-ray tubes;
A plurality of X-ray detectors constituting a plurality of pairs with the plurality of X-ray tubes, and the X-ray detectors each having a plurality of detection elements arrayed in a matrix with respect to a channel direction and a slice direction;
A support mechanism for rotatably supporting the X-ray tube and the X-ray detector around a rotation axis parallel to the slice direction;
In order to reduce scattered radiation components derived from X-rays generated by X-ray tubes other than the X-ray tubes constituting the pair, the X-rays that have passed through the slit mechanism are located within a region that is directly irradiated. A correction unit that corrects data of each detection element to be corrected by data of at least one detection element related to the same channel outside the region;
An X-ray CT apparatus comprising: a reconstruction unit that reconstructs image data based on the corrected data. A plurality of X-ray tubes;
A plurality of slit mechanisms each having a variable slit width provided in each of the plurality of X-ray tubes;
A plurality of X-ray detectors constituting a plurality of pairs with the plurality of X-ray tubes, and the X-ray detectors each having a plurality of detection elements arrayed in a matrix with respect to a channel direction and a slice direction;
A support mechanism for rotatably supporting the X-ray tube and the X-ray detector around a rotation axis parallel to the slice direction;
Projection data of each detection element located in an area directly irradiated with X-rays that have passed through the slit mechanism is corrected with scattered radiation data of at least one detection element related to the same channel outside the area. A correction unit;
Under a first mode in which data is collected using a single pair of the plurality of pairs, image data is reconstructed based on the projection data not subjected to the correction, and the plurality of pairs are used. An X-ray CT apparatus comprising: a reconstruction unit configured to reconstruct image data based on the corrected projection data under a second mode in which data collection is performed. A plurality of X-ray tubes;
A plurality of slit mechanisms each having a variable slit width provided in each of the plurality of X-ray tubes;
A plurality of X-ray detectors constituting a plurality of pairs with the plurality of X-ray tubes, and the X-ray detectors each having a plurality of detection elements arrayed in a matrix with respect to a channel direction and a slice direction;
A support mechanism for rotatably supporting the X-ray tube and the X-ray detector around a rotation axis parallel to the slice direction;
In order to support the setting of scanning conditions, imaging corresponding to the entire effective area of the X-ray detector is performed under a first mode in which data is collected using a single pair of the plurality of pairs. Under a second mode in which a plurality of candidates relating to a combination of slice thickness and the number of slices to be imaged are prepared and data is collected using the plurality of pairs, at least two rows of detection elements at both ends of the X-ray detector A setting support unit for preparing a plurality of candidates corresponding to a part of the effective area excluding
A control unit for controlling the slit mechanism according to a combination of the imaging slice thickness and the number of imaging slices selected according to the user instruction;
Data of each detection element located within a part of the effective region to which X-rays having passed through the slit mechanism are directly irradiated are corrected by data of at least one detection element related to the same channel outside the part. A correction unit to perform,
Reconstruction that reconstructs image data based on the corrected data under the second mode, and reconstructs image data based on data that is not subjected to the correction under the first mode. An X-ray CT apparatus. A plurality of X-ray tubes;
A plurality of slit mechanisms each having a variable slit width provided in each of the plurality of X-ray tubes;
A plurality of X-ray detectors constituting a plurality of pairs with the plurality of X-ray tubes, and the X-ray detectors each having a plurality of detection elements arrayed in a matrix with respect to a channel direction and a slice direction;
A support mechanism for rotatably supporting the X-ray tube and the X-ray detector around a rotation axis parallel to the slice direction;
Under a first mode in which data is collected using a single pair of the plurality of pairs, the slit mechanism is controlled to irradiate the entire effective area of the X-ray detector with X-rays. Under the second mode of collecting data using the plurality of pairs, the slit mechanism is controlled to irradiate a part of the effective area excluding at least two rows at both ends of the X-ray detector. A control unit,
A correction unit that corrects the data of each detection element located within the portion to which X-rays having passed through the slit mechanism are directly irradiated by data of at least one detection element related to the same channel outside the region. When,
Reconstruction that reconstructs image data based on the corrected data under the second mode, and reconstructs image data based on data that is not subjected to the correction under the first mode. An X-ray CT apparatus.   The X-ray CT apparatus according to claim 1, wherein the correction unit subtracts the value of the scattered radiation data from the value of the projection data.   The X-ray CT apparatus according to claim 1, wherein the correction unit subtracts an average value of scattered radiation data from detection elements at both ends of the same channel from the value of the projection data.   The X-ray CT apparatus according to claim 1, wherein the correction unit subtracts one scattered radiation data of detection elements at both ends related to the same channel from the value of the projection data.   The X-ray CT apparatus according to claim 1, wherein the correction unit subtracts a value of scattered radiation data of a nearby detection element related to the same channel from the value of the projection data.   An imaging axis connecting the focal point of the X-ray tube constituting the pair and the center of the X-ray detector connects the focal point of the X-ray tube constituting the other pair and the center of the X-ray detector. The X-ray CT apparatus according to claim 1, wherein the imaging axis is orthogonal to the rotation axis.

Images