JP2008051548A - Computer tomographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a TR type computer tomographic apparatus for photographing a tomographic image reduced in artifact. <P>SOLUTION: The computer tomographic apparatus has a radiation source 10, a radiation detector 11 for detecting the radiation transmitted through a specimen 21, a mechanism part 12 which relatively controls the radiation source 10 and the specimen 21 so as to linearly move then a plurality of times in the direction of crossing the radiation along the fan surface of the radiation and presets the stop position of rotation between the respective linear movements and next linear movements so as to be shifted from positions forming 180° mutually to relatively control the radiation source 10 and the specimen 21 so as to rotate them stepwise in the same direction and a data processing part 15 for inputting the transmission data of the specimen 21 output by the radiation detector 11 which detects the radiation during the respective linear movements and forms the tomographic image of the specimen from the transmission data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a TR-type computed tomography apparatus that combines translation and rotation.

As a kind of computed tomography apparatus (hereinafter referred to as “CT” as appropriate), a TR (Translate Rotate) type CT is well known (for example, see Non-Patent Document 1). As shown in FIG. 8A, the TR-type CT is a fan angle in an X-ray beam emitted from a radiation source F of the X-ray tube 101 and formed into a fan shape by a collimator (not shown). An X-ray beam 200 having a (radiation angle) θ ₀ minutes is detected by an X-ray detector 102 having N channels of 1ch to Nch. When the X-ray beam 200 detected by each channel of the X detector 102 is output as transmission data I (n), it is processed by a connected computer (not shown) to form a tomographic image.

  In the CT shown in FIG. 8A, a t moving mechanism (not shown) moves the rotary table 103 on which the subject 201 is placed in the t direction (forward translation). In CT, an X-ray beam that forms transmission data In (t) in each channel n is detected for each fixed pitch of the movement position t during the translation of the forward path. At the time when the forward translation is completed, the rotary table 103 is in the position of the dotted line shown in FIG.

Subsequently, in the CT shown in FIG. 8A, a rotation mechanism (not shown) rotates the rotary table 103 at the rotation angle of the fan angle θ _{0 with} the rotation center C as the rotation axis. By rotating the rotary table 103 in this way, the subject 201 placed on the rotary table 103 is step-rotated.

  Thereafter, in CT shown in FIG. 8A, the t moving mechanism (not shown) moves the rotary table 103 on which the subject 201 is placed in the reverse direction of the t direction (translation of the return path). In CT, the X-ray beam 200 that forms the transmission data In (t) of the subject 201 is detected in each channel n for every fixed pitch of the movement position t during translation of the return path. The transmission data In (t) is parallel transmission data detected in each channel n.

As described above, in the CT shown in FIG. 8A, the transmission data Ik, n (t) is obtained by setting the translation number to k while repeating the forward translation, the step rotation in a fixed direction, and the backward translation. By acquiring the parallel transmission data Iψ (t) for 180 ° with respect to the azimuth (hereinafter referred to as “subject reference orientation”) ψ (k, n) when the subject 201 is used as a reference, At an angle pitch of θ ₀ / N. In CT, the tomographic image of the subject 201 is reconstructed by a filtered back projection method or the like using parallel transmission data Iψ (t) obtained at K times (K is a natural number of 2 or more). ing. Here, the fan angle θ ₀ is obtained by 180 ° / K.

  In the reconstruction of the cross-sectional image in the conventional CT of the TR method, as shown in FIG. 8B, first, the parallel transmission data Iψ (t) is logarithmically converted into parallel transmission data Pψ (t), and the parallel transmission data is obtained. A high-frequency emphasis filter is applied in the t direction for each direction ψ with respect to Pψ (t), and a cross-sectional image is obtained by back-projecting the virtual lattice point along the X-ray beam 200 (ψ direction). Here, in order to obtain a cross-sectional image, it is necessary to perform back projection so that the rotation center projection position tc on the parallel transmission data Pψ (t) matches the rotation center C.

In the CT of the TR method, when back projection is performed, if the rotation center projection position tc does not coincide, a radial artifact for each fan angle θ ₀ is generated in the tomographic image. Therefore, in the CT of the TR system, the geometric position of the translation (t movement) is accurately set so that the rotation center projection position tc matches in order to prevent the occurrence of an artifact in the cross-sectional image. Often occurs and some radial artifacts remain. On the other hand, conventionally, by performing an even number of scans consisting of K times of translation (multiple scans) and adding the cross-sectional images obtained in each scan, the remaining radial artifact for each fan angle θ ₀ is canceled out. In addition, there is CT that uses a method for obtaining a good cross-sectional image (see, for example, Patent Document 1).
JP-A-11-108857 Yoshinori Iwai, “CT Scanner” Corona, February 20, 1979, first edition, p.15-17

However, in the conventional multiple scan in CT as described in Patent Document 1, there is a problem that radial artifacts having an angular pitch finer than the fan angle θ ₀ may remain in the cross-sectional image. Artifacts remain in the conventional CT because the number of channels N of the X-ray detector 102 is insufficient and the angular pitch (θ ₀ / N) of parallel transmission data is large. Therefore, it is possible to prevent artifacts remaining in the cross-sectional image by smoothing the image with the high cut filter or increasing the number of channels.

  On the other hand, when the image is smoothed, there arises a problem that the resolution is lowered. In addition, when the number of channels is increased, the detector and data collection system become complicated, and the channel pitch is reduced, so that, for example, the length, thickness and accuracy of the scattered radiation collimator installed between the channels are secured. And the influence of scattered radiation becomes a problem.

  In view of the above problems, an object of the present invention is to improve image quality by reducing artifacts in a cross-sectional image of TR CT.

In order to achieve the above object, the invention according to claim 1 radiates fan-shaped radiation covering θ ₀ along the imaging plane, with an angle of 180 ° / K being θ ₀ for a natural number K of 2 or more. A radiation source, a radiation detector having a plurality of detection channels for detecting the radiation transmitted through the subject in the range of at least θ ₀ along the imaging plane, and the subject along the imaging plane with the radiation The radiation source and the subject are relatively controlled so as to move linearly a plurality of times in the intersecting direction, and the radiation source and the subject are rotated stepwise about a rotation axis perpendicular to the imaging surface. A mechanism unit that relatively controls the positional relationship of the specimen; and the mechanism unit performs the linear movement, and the step rotation is performed in the same direction between each linear movement and the next linear movement. 2 × A mechanism control unit for moving the linear movement K times, a mechanism control unit configured to perform step rotation by setting a plurality of stop positions of the step rotation so as not to be at positions that are 180 ° from each other; And a data processing unit that inputs transmission data of the subject output from the radiation detector that detects the radiation during movement and generates a cross-sectional image of the subject from the transmission data. To do.

According to the present invention having the above-described configuration, the data processing unit obtains a cross-sectional image of the subject from the transmission data over 360 ° in the direction ψ of the subject reference. ° worth of transmission data, to each other, combined cancel the radial artifacts remaining in cross-section image for each fan angle theta _0, it can be obtained with less cross-sectional image artifacts. Also, since the 180 ° subject reference azimuth ψ for 180 ° and the 180 ° subject reference azimuth ψ opposite to each other are shifted so as not to overlap each other, the angular pitch of the transmission data azimuth ψ is complemented. Since the cross-sectional image is reconstructed, a cross-sectional image in which the remaining radial artifacts with fine angular pitch are reduced can be obtained.

  According to a second aspect of the present invention, in the computed tomography apparatus according to the first aspect, when the angle between the radiation paths detected by the adjacent detection channels is Δθ, the mechanism control unit The gist is that the plurality of stop positions of the step rotation are step-rotated so as to be shifted by Δθ / 2 from the positions forming 180 °.

  According to the present invention having the above configuration, the sectional image is reconstructed by complementing the angular pitch of the azimuth direction ψ of the transmission data at an interval of Δθ / 2, and thus the sectional image in which the radial artifacts of the remaining fine angular pitch are reduced Can be obtained.

According to a third aspect of the present invention, in the computed tomography apparatus according to the first or second aspect, when the angle between the radiation paths detected by the adjacent detection channels is Δθ, the mechanism control unit is Then, the linear movement with the step rotation of θ ₀ is executed K times, then the step rotation of θ ₀ + Δθ / 2 is executed once, and then the linear movement with the step rotation of θ ₀ is inserted K The main point is to make it run once.

  According to the present invention having the above-described configuration, the object reference orientation ψ of the radiation path can extend over 360 °, and the stop positions of the step rotations can be shifted by Δθ / 2 from the positions forming 180 °.

According to a fourth aspect of the present invention, in the computed tomography apparatus according to the first or second aspect, when the angle between the radiation paths detected by the adjacent detection channels is Δθ, the mechanism control unit is Then, the linear movement with the step rotation of θ ₀ is executed K times, then the step rotation of θ ₀ −Δθ / 2 is executed once, and then the linear movement with the step rotation of θ ₀ is inserted. The gist is to execute it K times.

  According to the present invention having the above-described configuration, the object reference orientation ψ of the radiation path can extend over 360 °, and the stop positions of the step rotations can be shifted by Δθ / 2 from the positions forming 180 °.

  According to a fifth aspect of the present invention, in the computed tomography apparatus according to any one of the first to fourth aspects, the data processing unit obtains the transmission data acquired during the movement of the linear movement for each detection channel. The gist of the invention is that a cross-sectional image of the subject is generated by back-projecting over 360 ° in the direction ψ with respect to the subject of the radiation path detected by the detection channel.

  According to the present invention configured as described above, a cross-sectional image can be obtained by continuously performing back projection over 360 ° by the filter-corrected back projection method.

  The invention according to claim 6 is the computed tomography apparatus according to any one of claims 1 to 5, wherein the radiation detector has the detection channel in a direction parallel to the imaging plane and a direction orthogonal to the imaging plane. The gist is to have multiple rows.

  According to the present invention having the above-described configuration, a plurality of cross-sectional images can be obtained by 2 × K movements including step rotation, that is, one scan.

  The image quality of the cross-sectional image of the TR type CT can be improved.

[First Embodiment]
FIG. 1A is a plan view of the configuration of the computed tomography apparatus (CT) 1 according to the first embodiment of the present invention observed from above, and FIG. 1B is the computed tomography apparatus 1. It is the front view which observed the structure of from the horizontal direction.

  As shown in FIG. 1, the computed tomography apparatus 1 includes an X-ray tube 10 that emits an X-ray beam 20 along an imaging plane 22 that is a horizontal plane set as a plane for obtaining a cross-sectional image, and an imaging plane 22. And an X-ray detector 11 for detecting the X-ray beam 20 transmitted through the subject 21 in each channel. In the X-ray detector 11, for example, a semiconductor optical sensor and a scintillator are combined, and radiation is generated from the radiation generation source F. In FIG. 1, it is assumed that the number of detection channels is N, the X-ray beam 20 is detected in each channel of the X-ray detector 11, and transmission data I (n) is output.

As shown in FIG. 1B, the X-ray tube 10 and the X-ray detector 11 are supported by the mechanism unit 12 so as to face each other. The X-ray beam 20 generated from the focal point F of the X-ray beam 20 of the X-ray tube 10 has an angle θ ₀ determined by a collimator (not shown) at 180 ° / K (K is a natural number of 2 or more). As a corner, it is formed into a fan shape with an angle covering at least θ ₀ , and enters the X-ray detector 11 as shown in FIG. As described above, since θ ₀ = 180 ° / K with respect to K, if K = 6, the fan angle θ ₀ is 30 °. The X-ray detector 11 detects an X-ray beam 20 in an angle range covering at least θ ₀ along the imaging surface 22 and uses the detected transmission data for θ _{0 of} this. Hereinafter, it is described as detecting only θ ₀ minutes.

  Further, the computer tomography apparatus 1 includes a mechanism unit 12 that controls a rotary table 13 on which the subject 21 is placed, as shown in FIG. Specifically, the mechanism unit 12 includes K × 2 reciprocating linear movements (hereinafter referred to as “transformers”) in the direction t in which the subject 21 intersects the X-ray beam 20 along the imaging surface 22, including the forward path and the return path. The movement of the rotary table 13 on which the subject 21 is placed is controlled so as to perform “rate” or “t movement”. Further, the mechanism unit 12 performs step rotation of a predetermined angle in the same direction around the rotation axis 23 passing through the rotation center C perpendicular to the imaging surface 22 between each linear movement and the next linear movement. The rotation of the turntable 13 is controlled.

  The predetermined angle is set in advance so that the plurality of stop positions (any two of the step rotations) are not 180 ° from each other, so that the subject of the radiation path detected by each detection channel is set. This is the step rotation angle at which the step rotation is performed so that the reference azimuth ψ does not overlap with the opposite direction of the radiation path at the position where the angle is 180 °. Further, the predetermined angle is a step rotation angle set in advance so that a plurality of stop positions of the step rotation is 360 ° so that the azimuth ψ with respect to the subject of the radiation path detected by the detection channel does not come off.

  Further, the mechanism unit 12 controls the imaging part of the subject 21 placed on the rotating table 13 to be aligned with the imaging surface 22 by raising and lowering the rotating table 13 according to a control signal input from the outside.

  The sequence of t movement and step rotation controlled by the mechanism unit 12 is stored in the mechanism control unit 14 shown in FIG. The mechanism control unit 14 inputs a start command from the data processing unit 15 to which a request for starting tomography is input by the operator, and outputs a control signal to the mechanism unit 12 for executing TR scan processing according to a stored sequence. To do. When the operator inputs a request for controlling the raising / lowering of the rotary table 13, a control signal for raising / lowering the rotary table 13 is output to the mechanism unit 12.

  As shown in FIG. 1B, the computed tomography apparatus 1 includes a data processing unit 15 and X detected by the X-ray detector 11 at a number of movement positions during movement of 2 × K times. The transmission data I (n) converted from the line beam 20 is input to reconstruct a cross-sectional image of the subject 21 on the imaging surface 22. The data processing unit 15 is a general computer that includes a central processing unit, a storage device, a memory, and the like, and stores software and the like for reconstructing a cross-sectional image. The data processing unit 15 reconstructs a cross-sectional image from transmission data detected by the X-ray detector 11 using a “filter-corrected back projection method” that has been generally used conventionally. In addition, the data processing unit 15 has an input unit through which requests for various operations are input by an operator.

  Other components of the computer tomography apparatus 1 are a display unit 16 connected to the data processing unit 15 for displaying a tomographic image, an X-ray control unit for controlling the X-ray tube 10, and X-rays leaking to the outside. There are X-ray shielding boxes and the like (not shown).

Next, the relationship between each channel of the X-ray beam 20 and the X-ray detector 11 will be described with reference to FIG. In FIG. 2 and the following description, the angle between the X-ray paths detected by the adjacent detection channels is Δθ. Here, the angle Δθ formed by adjacent X-ray paths is substantially constant, but is not strictly the same angle. For example, when the X-ray detector 11 has a unit structure composed of a plurality of detector units, the joints of the detectors that are the units are inhomogeneous. Further, when the detection channels are linearly arranged at equal intervals, the angle Δθ formed by the two X-ray paths existing at the end is smaller than the angle Δθ formed by the two central X-ray paths p. In the embodiment of the present invention described below, an average value of angles between adjacent X-ray paths is used as Δθ. Specifically, when the X-ray detector 11 has N channels (1, 2,..., N), the angle between the X-ray paths with respect to the fan angle θ ₀ is Δθ = θ ₀ / N. Therefore, the angle formed by the radiation paths p ₁ and p ₂ is approximately Δθ, and the angle formed by the radiation paths p ₂ and p ₃ is also approximately Δθ. The angle formed by any other adjacent radiation path is also approximately Δθ.

<< TR scan processing in computed tomography system >>
In the computed tomography apparatus 1, after the rotary table 13 on which the subject 21 is placed is moved up and down and the imaging region of the subject 21 is aligned with the rotation center C, the TR scan start operation command input by the operator is input. To start a TR scan. The data processing unit 15 outputs a scan start command to the mechanism control unit 14 when a start operation command is input by the operator. As a result, the mechanism control unit 14 outputs a control signal for controlling the TR scan to the mechanism unit 12 in accordance with a sequence stored in advance. The mechanism control unit 14 at this time, the mechanism unit 12, to execute the t movement of K times across the step rotation of the theta _0, a step rotation of the next θ ₀ + Δθ / 2 (or θ ₀ -Δθ / 2) After that, a control signal is output so that K times of t movement are executed with a step rotation of θ ₀ interposed therebetween.

With reference to FIG. 3 and Table 1, the process for executing the TR scan in the computed tomography apparatus 1 will be specifically described. 3 and Table 1, a case where K = 6 and θ ₀ = 30 ° will be described. A series of processing described below is one TR scan, and is executed by a sequence stored in the mechanism control unit 14.

  When the TR scan is started in the computed tomography apparatus 1, the mechanism unit 12 moves the subject 21 by t (outward) so as to cross the X-ray beam 20 by moving the rotary table 13 by t (S01). The X-ray detector 11 detects the X-ray beam 20 at each of a large number of positions at a constant movement interval (fixed pitch) during the movement of t movement, and outputs it to the data processing unit 15 as transmission data I (n). .

  When the t movement (outward path) is completed, the mechanism unit 12 rotates the rotary table 13 on which the subject 21 is placed by 30 ° (S02).

  When the step rotation is completed, the mechanism unit 12 moves the subject 21 by t (return path) across the X-ray beam 20 by moving the rotary table 13 in the opposite direction to step S01 (S03). The X-ray detector 11 detects the X-ray beam 20 at each of a large number of positions at a fixed movement interval (fixed pitch) during the movement of t movement, and outputs it to the data processing unit 15 as transmission data I (n).

  When the t movement (return path) ends, the mechanism unit 12 rotates the rotary table 13 on which the subject 21 is placed by 30 ° in the same direction as the direction rotated in step S02 (S05).

  The processes in steps S01 to S05 described above are repeated until the t movement of the t movement number 6 is completed. When the t movement of the t movement number 6 is completed (YES in S04), the mechanism unit 12 is placed on the subject 21. The rotary table 13 is rotated by 30 ° + Δθ / 2 steps in the same direction as the direction rotated in step S02 (S06).

  Subsequently, the mechanism unit 12 moves the subject 21 by t (outward) across the X-ray beam 20 by moving the rotary table 13 in the same direction as step S01 (S07). The X-ray detector 11 detects the X-ray beam 20 at each of a large number of positions at a fixed movement interval (fixed pitch) during the movement of t movement, and outputs it to the data processing unit 15 as transmission data I (n).

  When the t movement (outward path) ends, the mechanism unit 12 rotates the rotary table 13 on which the subject 21 is placed by 30 ° in the same direction as the direction rotated in step S02 (S08).

  When the step rotation ends, the mechanism unit 12 moves the subject 21 by t (return path) across the X-ray beam 20 by moving the rotary table 13 in the direction opposite to that in step S07 (S09). The X-ray detector 11 detects the X-ray beam 20 at each of a large number of positions at a fixed movement interval (fixed pitch) during the movement of t movement, and outputs it to the data processing unit 15 as transmission data I (n).

  When the t movement (return path) ends, the mechanism unit 12 rotates the rotary table 13 on which the subject 21 is placed by 30 ° in the same direction as the direction rotated in step S02 (S11). Thereafter, the processes in steps S07 to S11 are repeated until the t movement of the t movement number 12 is completed. When the t movement of the t movement number 12 is completed (YES in S10), the mechanism unit 12 ends the TR scan.

  As shown in Table 1, for example, at the time when t movement of t movement number 1 is finished, the rotation angle φ from the initial position (accumulation of step rotation) is 0 °, and t movement of t movement number 2 starts. Before being rotated, the rotation angle is 30 ° by 30 ° step rotation. Further, when the t movement of the t movement number 6 is finished, the rotation angle is 150 °, and before the t movement of the t movement number 7 is started, the rotation angle is rotated by 30 ° + Δθ / 2 steps and the rotation angle is 180 °. + Δθ / 2. Furthermore, when the t movement of t movement number 12 is finished, the rotation angle is 330 ° + Δθ / 2.

  FIG. 4 shows t movement number 1 (φ = 0 °) and t movement number 7 (φ = 180 °) at the mutually opposite stop positions of the step rotation when the TR scan described with reference to FIG. 3 and Table 1 is performed. The relationship of the azimuth | direction (psi) of the X-ray path p represented by the subject reference | standard about + (DELTA) (theta) / 2) is shown. The subject reference azimuth ψ of the X-ray path is measured from the center of the X-ray detector 11 along the imaging surface 22 of the X-ray path p detected by the rotation angle φ (k) at channel t and channel n. The sum of the set angles θ (n), which is the angle, is expressed by equation (1).

ψ (k, n) = φ (k) + θ (n) (1)
The opposing stop position refers to a stop position that forms approximately 180 ° with respect to a stop position having a rotation angle φ.

The number of detection channels of the X-ray detector 11 is actually 100 channels or more, but in FIG. 4, for the sake of convenience, it is set to 4 channels (1ch to 4ch). As shown in FIG. 4, the rotational positions of t movement numbers 1 and 7 are shifted from each other by Δθ / 2 from 180 °, and are complementary to each other in the angular pitch of the detected X-ray path. For example, in the example shown in FIG. 4, the opposed X-ray paths p ₁ and p ₁ ′, X-ray paths p ₂ and p ₂ ′, X-ray paths p ₃ and p ₃ ′, X-ray paths p ₄ and p ₄ ′. Are opposite to each other and their directions are shifted by Δθ / 2. Further, as shown in Table 1, the rotational positions of all other rotational position pairs that are not shown in FIG. 4 and that are at the opposite stop positions are shifted from each other by 180 ° from Δθ / 2. Thereby, X-ray paths are formed at intervals of Δθ / 2 over 360 ° by complementing with reverse paths. Therefore, by the TR scan that repeats the t movement and the step rotation described above with reference to FIG. 3, the transmission data forming an X-ray path that complements the angular pitch with each other in a reverse direction so that ψ spans 360 ° is captured. Can do.

  When the t movement number is k, the number of channels of the X-ray detector is n, and the t movement position is t, the data processing unit 15 acquires each by 2 × K t movements (ψ (k, n)) Transmission data I (ψ, t) (over 360 °) to 360 ° by the filter-corrected backprojection method with an object reference orientation ψ (k, n) of the X-ray path defined by the detection channel for each detection channel. Back projection is performed to obtain a cross-sectional image of the subject.

According to the CT1 according to the first embodiment described above, the angular pitch Δθ (Δθ = θ ₀ / N) of the direction ψ of the transmission data I (ψ, t) is complemented, and back projection is performed at an interval of Δθ / 2. As a result, it is possible to obtain a cross-sectional image in which the remaining fine radial pitch radial artifacts are reduced.

  Moreover, according to CT1 which concerns on 1st Embodiment mentioned above, when backprojecting, it considers inhomogeneous arrangement | positioning of a detection channel, and (psi) (k, n) calculated by Formula (1) is used. Projection can be performed accurately, and a cross-sectional image can be obtained in which the remaining radial artifacts with fine angular pitch are further reduced.

Furthermore, according to CT1 which concerns on 1st Embodiment mentioned above, by backprojecting the transmission data of 0 degree-360 degrees, backprojection for 180 degrees and backprojection for 180 degrees opposite to this are performed. Thus, the radial artifacts that remain after each fan angle θ ₀ can be canceled out, and a good cross-sectional image can be obtained. In Patent Document 1 described above, a scan composed of K times of translation with step rotation interposed is performed twice while continuing step rotation in the same direction (double scan), and cross-sectional images obtained by each scan are mutually obtained. A method is described in which the remaining radial artifacts for each fan angle θ ₀ are canceled out by rotating 180 ° and performing addition. The reason for adding by rotating 180 degrees in Patent Document 1 is that the same back projection is performed in each scan. That is, the transmission data of 0 ° to 180 ° is back-projected at 0 ° to 180 ° in the first scan to create a cross-sectional image, and the transmission data of 180 ° to 360 ° is 0 ° to 180 ° in the second scan. The back view is used to make a cross-sectional image. Here, if back projection is performed at 180 ° to 360 ° in the second scan, the cross-sectional image is not reversed, and if the two cross-sectional images are added as they are, the same cross-sectional image can be formed. Further, the same cross-sectional image can be obtained even if the transmission data of 0 ° to 360 ° is continuously back-projected at 0 ° to 360 °.

  In the first embodiment, the rotation of 30 ° + Δθ / 2 is performed in step S06 of the flowchart of FIG. 3. However, even if the rotation of 30 ° −Δθ / 2 is reversed with the sign of Δθ reversed, the direction ψ It can be easily understood that transmission data forming an X-ray path over 360 ° and complementing the angular pitch with each other in reverse directions can be acquired.

<Second Embodiment>
The computed tomography apparatus according to the second embodiment of the present invention replaces the X-ray detector 11 of the computed tomography apparatus 1 according to the first embodiment of the present invention with the X-ray detector shown in FIG. 11a. FIG. 5 shows a state in which the X-ray detector 11a is viewed from the side opposite to the side on which the X-ray beam 20 is incident, but the X-ray detector 11a has a channel direction parallel to the imaging plane 22 and the imaging plane 22. A plurality of detection channels are provided in a column direction orthogonal to. The other configuration of the computed tomography apparatus according to the second embodiment is the same as that of the computed tomography apparatus 1 according to the first embodiment described above with reference to FIG.

  The TR scan method in the computed tomography apparatus according to the second embodiment is the same as that of the computed tomography apparatus 1 according to the first embodiment described above with reference to FIGS. Since the X-ray detector 11a has a plurality of channel rows, the transmission data I (k, n, t) corresponding to the number of channel rows is obtained as compared with the computed tomography apparatus according to the first embodiment. Obtainable. The computed tomography apparatus according to the second embodiment performs the same reconstruction as that of the first embodiment for each of I (k, n, t). Therefore, in the computed tomography apparatus according to the second embodiment, it is possible to obtain cross-sectional images for the number of channel rows (for the number of sheets) by one TR scan.

  However, when the number of columns increases, in the above-described reconstruction, as the columns are shifted from the imaging surface 22, the inclination of the X-ray path from the imaging surface 22 increases, so that the cross-sectional image deteriorates. In this case, a known cone beam reconstruction method is used. In this cone beam reconstruction method, when the column number of the X-ray detector 11a is m and the transmission data is represented by I (m, k, n, t), the transmission data I ((m, t) plane I ( m, t) are set as one set, the direction ψ (k, n) is constant (parallel), the direction of the rotation axis 23 is inclined toward the focal point, and the projection is performed on the three-dimensional virtual matrix. Here, the pitch of the virtual matrix can be set arbitrarily, and may be the same or different between the rotation axis and the two axes orthogonal thereto. The matrix size can also be set arbitrarily, and an arbitrary number of cross-sectional images can be obtained regardless of the number of columns. For example, the ψ range is changed from 180 ° to 360 ° by a known reconstruction method described in JP-A-2005-361747.

  As described above, when using the X-ray detector 11a having a two-dimensional detection matrix having a large number of columns M, cone beam reconstruction is used in order to prevent deterioration of a cross-sectional image at a position shifted from the imaging surface 22. Is preferred.

According to the CT according to the second embodiment, similarly to the CT according to the first embodiment, the angle pitch Δθ (= θ ₀ / N) of the azimuth ψ of the transmission data I (n) is complemented, and Δθ / Since back projection is performed at intervals of 2, it is possible to obtain a cross-sectional image in which the remaining radial artifacts with fine angular pitch are reduced. Further, according to the CT according to the second embodiment, when back projection is performed, by using ψ (k, n) calculated by the above equation (1) in consideration of the heterogeneous arrangement of the detection channels, Projection can be performed accurately, and a cross-sectional image can be obtained in which the remaining radial artifacts with fine angular pitch are further reduced. Furthermore, according to the CT according to the second embodiment, it is possible to obtain a cross-sectional image in which the remaining radial artifacts for each fan angle θ ₀ are canceled out. Further, according to the CT according to the second embodiment, a plurality of cross-sectional images can be obtained by one scan.

<First Modification>
Subsequently, a first modification of the computed tomography apparatus according to the first and second embodiments will be described. The configuration of the computed tomography apparatus according to the first modification is the same as that of the computed tomography apparatus 1 described above with reference to FIG. 1, but the processing according to the first modification is described with reference to FIG. As will be described, the sequence stored in the mechanism control unit 14 is different.

In FIG. 6 and Table 2, it is assumed that K = 6 and θ ₀ = 30 °. When the TR scan is started in the computed tomography apparatus according to the first modification, the mechanism unit 12 moves the subject 21 by moving the rotation table 13 to cross the X-ray beam 20 (outward path). (S21). The X-ray detector 11 detects the X-ray beam 20 at each of a number of positions at a fixed movement interval (fixed pitch) during the movement of t movement, and outputs it to the data processing unit 15 as transmission data I (n). .

  When the t movement (outward path) ends, the mechanism unit 12 rotates the rotary table 13 on which the subject 21 is placed by 30 ° + Δθ / 2 steps (S22).

  When the step rotation ends, the mechanism unit 12 moves the subject 21 in the reverse direction so as to cross the X-ray beam 20 by moving the rotary table 13 in the direction opposite to that in step S21 (S23). ). The X-ray detector 11 detects the X-ray beam 20 at each of a large number of positions at a constant movement interval (a constant pitch) during the movement of t movement, and outputs it to the data processing unit 15 as transmission data I (n). .

  When t movement (return path) is completed, the mechanism unit 12 rotates the rotary table 13 on which the subject 21 is placed by 30 ° −Δθ / 2 steps in the same direction as the direction rotated in step S22 (S25).

  The processes in steps S21 to S25 described above are repeated until the t movement of the t movement number 6 is completed. When the t movement of the t movement number 6 is completed (YES in S24), the mechanism unit 12 places the subject 21 thereon. The rotary table 13 is rotated by 30 ° in the same direction as the direction rotated in step S22 (S26).

  Subsequently, the mechanism unit 12 moves the subject 21 by t (outward) across the X-ray beam 20 by moving the rotary table 13 in the same direction as step S21 (S27). The X-ray detector 11 detects the X-ray beam 20 at each of a large number of positions at a fixed movement interval (fixed pitch) during the movement of t movement, and outputs it to the data processing unit 15 as transmission data I (n).

  When the t movement (outward path) ends, the mechanism unit 12 rotates the rotary table 13 on which the subject 21 is placed by 30 ° −Δθ / 2 steps in the same direction as the direction rotated in step S22 (S28).

  When the step rotation ends, the mechanism unit 12 moves the subject 21 in the reverse direction so as to cross the X-ray beam 20 by moving the rotary table 13 in the direction opposite to that in step S27 (S29). ). The X-ray detector 11 detects the X-ray beam 20 at each of a large number of positions at a fixed movement interval (fixed pitch) during the movement of t movement, and outputs it to the data processing unit 15 as transmission data I (n).

  When t movement (return path) is completed, the mechanism unit 12 rotates the rotary table 13 on which the subject 21 is placed by 30 ° + Δθ / 2 steps in the same direction as the direction rotated in step S22 (S31). Thereafter, the processes of S27 to S31 are repeated until the t movement of the t movement number 12 is completed.

  As shown in Table 2, for example, when the t movement of the t movement number 1 is finished, the rotation angle from the initial position (accumulation of the step rotation) is 0 °, and the t movement of the t movement number 2 is started. Is rotated by 30 ° + Δθ / 2 steps before the rotation angle becomes 30 ° + Δθ / 2. Further, when the t movement of the t movement number 6 is finished, the rotation angle is 150 ° + Δθ / 2, and the rotation angle is 180 ° by rotating 30 steps before the t movement of the t movement number 7 is started. + Δθ / 2. Furthermore, when the t movement of the t movement number 12 is finished, the rotation angle is 330 °.

  As described above, if the mechanism control unit 14 controls the mechanism unit 12 to perform step rotation as shown in Table 2, the counter rotation stop position of the step rotation is shifted by Δθ / 2 from 180 °, and the X-ray path It is possible to prevent the subject reference azimuth ψ from extending over 360 ° and the azimuth ψ from overlapping each other in a reverse path.

<Second Modification>
As shown in FIG. 7, the computed tomography apparatus 3 according to the second modified example detects an X-ray beam 20 irradiated from an X-ray tube 30 and transmitted through a subject 21 with an X-ray detection having a two-dimensional channel matrix. Although the configuration is the same as that of the second embodiment in that the image is detected by the device 31, the mechanism for t movement and rotation is different. That is, in the computed tomography apparatus according to the first and second embodiments described above with reference to FIG. 1, the subject 21 is translated (t movement) and rotated. However, in the computed tomography apparatus according to the second modification, the subject 21 is fixed, and the X-ray tube 30 and the X-ray detector 31 are integrally translated (t movement) and rotated. By controlling the movement in this way, the relationship between the X-ray tube 30 and the X-ray detector 31 and the subject 21 is relatively equivalent to the case where the subject 21 is controlled to move as described above. Become.

  Specifically, in the computed tomography apparatus 3 according to the second modification, the subject 21 is placed on the XYZ mechanism 35 supported by the floor 34. The subject 21 can be moved with respect to the X-ray beam 20 in the X, Y, and Z directions by the XYZ mechanism 35, but is fixed at the moved position during scanning.

  In the computed tomography apparatus 3, the rotating mechanism 36 is supported by the floor 34, the rotating mechanism 36 supports the t moving mechanism 37, and rotates the entire t moving mechanism 37 with the t moving direction. The t moving mechanism 37 supports the frame 38, and the t moving mechanism 37 can move the frame 38 in the t moving direction. The X-ray tube 30 and the X-ray detector 31 face each other and are fixed by a frame 38. In the computed tomography apparatus 3, the t movement direction is a direction perpendicular to the paper surface at the rotation position shown in FIG. 7, but rotates together with the frame 38 and the t movement mechanism 37.

  Although not shown, the computed tomography apparatus 3 shown in FIG. 7 has the same configuration as the computed tomography apparatus 1 shown in FIG. Therefore, also in the computed tomography apparatus 3, the t moving mechanism 37 is controlled by the sequence stored in the mechanism control unit to move the frame 38 that fixes the X-ray tube 30 and the X-ray detector 31 and to rotate the rotating mechanism 36. Is rotated around the rotation axis 23 to take a cross-sectional image of the subject 21.

  Thus, the computer tomography apparatus 3 shown in FIG. 7 can also perform a relatively equivalent TR scan.

  As described above in the second modification, as long as the mechanism operation is relatively equivalent, the same applies to other mechanism systems.

<Other variations>
In the first and second embodiments described above, the range of the fan angle θ ₀ of the X-ray beam 20 is detected, but it may be detected exceeding θ ₀ . In this case, transmission data is acquired at overlapping azimuths ψ by adjacent t movements. For example, as described in Japanese Patent Application Laid-Open No. 2005-361741, the transmission data is weighted and averaged with weights. Can be reconfigured.

  In the first and second embodiments described above, the data processing unit 15 back-projects transmission data over 360 ° at the subject reference orientation ψ over 360 ° to obtain a cross-sectional image of the subject. However, even if the transmission data is divided into multiple parts by ψ, each is backprojected to reconstruct an incomplete cross-sectional image (partial image), and each partial image is added to create a cross-sectional image Are equivalent. For example, partial images may be created at the first 180 ° and the next 180 °, added, and averaged.

In the first embodiment and the first modification described above, the sets of the two rotation stop positions at the opposite stop positions are all shifted from each other by 180 ° from Δθ / 2. This shift is not limited to Δθ / 2. For example, i may be an integer and generally shifted by ± (Δθ / 2 + i · Δθ). Furthermore, i may be a different number for each group. Here, when the absolute value of the shift amount exceeds Δθ / 2, detection is made to exceed θ ₀ in order to prevent a gap from occurring in the direction ψ covered by the adjacent t movement. Then, the used channel range is adjusted every t movement so that no omission or overlap occurs in ψ.

  In the first and second embodiments described above, the method for reconstructing a tomographic image is not limited to the filtered back projection method, and a known algorithm such as a Fourier transform method or ART (Algebraic Reconstruction Technique) is used. Also good.

  In the first and second embodiments described above, X-rays are used as the radiation. However, as long as the radiation is transmissive, the same applies to other radiation such as γ-rays, neutrons, and microwaves. It is. The same applies to visible light when the subject is a transparent object.

1 is a conceptual diagram of a computed tomography apparatus according to a first embodiment of the present invention. It is a figure explaining the space | interval of the X-ray path in the computed tomography apparatus concerning the 1st Embodiment of this invention. It is a flowchart explaining the process of TR scan in the computed tomography apparatus concerning the 1st Embodiment of this invention. It is a figure explaining the opposing path | pass of the X-ray in the computed tomography apparatus concerning the 1st Embodiment of this invention. It is a figure explaining the X-ray detector of the computer tomography apparatus which concerns on the 2nd Embodiment of this invention. It is a flowchart explaining the process of TR scan in the computed tomography apparatus which concerns on the 1st modification of this invention. It is a conceptual diagram of the computer tomography apparatus which concerns on the 2nd modification of this invention. The figure explaining TR scan of the conventional computer tomography apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Computer tomography apparatus 10 ... X-ray tube (radiation source)
11 ... X-ray detector (radiation detector)
DESCRIPTION OF SYMBOLS 12 ... Mechanism part 13 ... Rotary table 14 ... Mechanism control part 15 ... Data processing part 16 ... Display part 20 ... X-ray beam (radiation)
21 ... Subject 22 ... Imaging surface 23 ... Rotation axis

Claims (6)

For a natural number K of 2 or more, an angle of 180 ° / K is θ ₀ .
A radiation source that emits fan-shaped radiation covering θ ₀ along the imaging plane;
A radiation detector having a plurality of detection channels for detecting the radiation transmitted through the subject in the range of at least θ ₀ along the imaging surface;
The radiation source and the subject are relatively controlled so that the subject moves linearly a plurality of times in a direction intersecting the radiation along the imaging surface, and a rotation axis perpendicular to the imaging surface is provided. A mechanism for relatively controlling the positional relationship between the radiation source and the subject so as to rotate stepwise as a center;
A mechanism control unit for causing the mechanism unit to perform the linear movement, and to perform the step rotation in the same direction between each linear movement and the next linear movement to perform the linear movement of 2 × K times. And a mechanism control unit for setting and shifting the step rotation in advance so that the plurality of stop positions of the step rotation are not 180 ° from each other, and a step rotation,
A data processing unit that inputs the transmission data of the subject output by the radiation detector that has detected the radiation during each of the linear movements, and generates a cross-sectional image of the subject from the transmission data;
A computer tomography apparatus characterized by comprising: The computed tomography apparatus according to claim 1, wherein the angle between the radiation paths detected by each of the adjacent detection channels is Δθ,
The computer tomography apparatus, wherein the mechanism control unit causes the mechanism unit to perform step rotation so that a plurality of stop positions of the step rotation are shifted by Δθ / 2 from positions that form 180 ° with respect to each other. The computed tomography apparatus according to claim 1 or 2, wherein the angle between the radiation paths detected by each of the adjacent detection channels is Δθ,
The mechanism control unit causes the mechanism unit to execute the linear movement with the step rotation of θ ₀ sandwiched K times, then to perform the step rotation of θ ₀ + Δθ / 2 once, and then the step of θ ₀ A computed tomography apparatus characterized in that the linear movement with rotation is performed K times. The computed tomography apparatus according to claim 1 or 2, wherein the angle between the radiation paths detected by each of the adjacent detection channels is Δθ,
The mechanism control unit causes the mechanism unit to execute the linear movement with a step rotation of θ ₀ K times, then to perform a step rotation of θ ₀ −Δθ / 2 once, and then to θ ₀ A computed tomography apparatus, wherein the linear movement with step rotation is performed K times. The computed tomography apparatus according to any one of claims 1 to 4,
The data processing unit spans 360 ° in an azimuth direction ψ with respect to the subject of the radiation path detected by the detection channel for each detection channel of the transmission data acquired during each of the linear movements. A computer tomography apparatus that generates a cross-sectional image of a subject by back projection. The computed tomography apparatus according to any one of claims 1 to 5,
The radiation detector has a plurality of rows of detection channels in a direction parallel to the imaging plane and a direction orthogonal to the imaging plane.

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