JP2003061946A - Ct apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CT apparatus capable of preventing development of a false image in outputting a reconfiguration image according to a reconfiguration visual field. SOLUTION: This apparatus is provided with a main detector 42A and a sub-detector 42B. When extended transmitted X-ray covering the reconfiguration visual field is detected by the main detector 42A, the X-ray transmitted outside the main detector 42A is detected by the sub-detector 42B. The transmission data of a part outside the reconfiguration visual field, which is easy to be shortage in performing convolution processing is compensated to create a convolution profile (CVP), and according to the CVP, a reconfiguration image corresponding to the reconfiguration visual image is created.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CT device used for nondestructive measurement in the medical field or industrial field, and more particularly,
The present invention relates to a technique for preventing a false image that occurs when a reconstructed image is output.

[0002]

2. Description of the Related Art Conventionally, as an X-ray CT apparatus of this type, as shown in FIG. 12, an X-ray tube 41 for irradiating a subject M with X-rays, and an X-ray tube 41 sandwiching the subject M therebetween. Flat panel type X-ray detectors 42 (hereinafter, simply referred to as "X
X-ray tube 41 and X-ray tube 42)).
In some cases, the line detector 42 rotates in synchronization with the subject M in the direction of the arrow RA.

The size of the X-ray detector 42 used in this X-ray CT apparatus is normally 17 inches square, while the diameter of the gantry opening G is 600 mm. Therefore, the cone-beam X-ray transmission image transmitted through the subject M and detected by the X-ray detector 42 must have a diameter of about 240 mm when the subject M is placed on the center of the gantry. It has to be done. That is,
The range of the reconstruction field of view is 240 mm in diameter, and the transmitted X-ray having a spread corresponding to the reconstruction field V is the X-ray detector 42.
Is detected on the entire surface of.

[0004]

However, the conventional device having such a structure has the following problems. That is, CT is performed under the condition that the range (diameter) of the reconstruction field of view is 240 mm (max) with the conventional X-ray CT apparatus.
There is a problem that a false image occurs when imaging is performed, convolution processing is performed with transmission data based on a detection signal obtained from an X-ray detector, and a reconstructed image is output.

For example, as shown in FIG. 12, when CT imaging is performed on a subject M which is a patient, an actual whole body scan is actually executed. At this time, although the body part of the subject M is substantially within the reconstruction field of view V, the arm part M1 and the like are not included in the reconstruction field of view V.
It will stick out.

When the convolution processing is executed in such a state, the transmission data detected at the end of the X-ray detector 42 is obtained by transmitting a part of the arm M1 and the like out of the reconstruction field of view. If the transmitted data is not used, a false image will occur due to lack of data.

The present invention has been made in view of the above circumstances, and provides a CT apparatus which supplements data that tends to be lacking in a portion out of the reconstruction field of view and does not generate a false image in a reconstruction image. The main purpose is to do.

[0008]

The present invention has the following constitution in order to achieve such an object. That is, the invention according to claim 1 is: (a) an irradiation means for irradiating an electromagnetic wave having a transmissivity in the form of a divergent beam toward the subject placed on the top plate, and (b) sandwiching the subject. In the detection means, which is arranged to face the irradiation means, includes a plurality of detection elements for detecting electromagnetic waves transmitted through the subject,
(C) A CT including a first driving unit that relatively rotationally moves the irradiation unit and the detection unit around the subject so that the electromagnetic wave scans around the subject.
In the apparatus, the detection means includes: (d) a main detector that detects an electromagnetic wave having a spread that covers the reconstruction field of view;
(E) a sub-detector for detecting an electromagnetic wave that has passed through the main detector and is transmitted, and the density of the detection elements of the sub-detector is smaller than that of the main detector. is there.

The invention described in claim 2 is the same as claim 1.
(F) Each of the detection elements of the main detector and the sub-detector is (2) arranged two-dimensionally.

The invention described in claim 3 is the same as claim 1
Alternatively, in the CT apparatus according to claim 2, (g) the detection elements of the sub-detector are arranged such that the density decreases as the distance from the boundary line of the reconstruction field of view of the main detector increases. To do.

The invention described in claim 4 is the same as claim 1.
In the CT device according to any one of claims 1 to 3,
(H) While the irradiation unit and the detection unit are relatively rotationally moved around the subject, the central axis of the electromagnetic wave emitted from the irradiation unit passes through the center of the region of interest, which is the imaging target, and It is characterized in that it is provided with a second drive means for previously adjusting the three-dimensional position of the subject so as to be incident on the center point of the detection surface of the detector.

The invention described in claim 5 is the same as claim 1.
In the CT device according to any one of claims 1 to 3,
(I) While the irradiation unit and the detection unit are relatively rotationally moved around the subject, the central axis of the electromagnetic wave emitted from the irradiation unit passes through the center of the region of interest, which is the imaging target, and It is characterized in that a third driving means for displacing the main detector is provided so as to be incident on the center point of the detection surface of the detector.

Further, in the invention according to claim 6, (j) the set of the irradiation means and the detection means and the subject are moved relatively to each other, and the electromagnetic wave spirals around the subject. A control means for controlling the first drive means so as to scan is provided.

[Operation] The operation of the invention described in claim 1 is as follows. That is, data that tends to be insufficient in transmission data obtained by detecting an electromagnetic wave with a spread that covers the reconstruction field of view by the main detector is supplemented based on the electromagnetic wave deviated from the main detector detected by the sub detector. To be done. That is, when executing the reconstructed image processing, it is possible to prevent occurrence of a false image due to lack of transparent data.

Further, since the density of the detection elements of the sub-detector is smaller than the density of the main detector, the number of data to be detected is reduced. As a result, the arithmetic processing can be speeded up and the detector itself The configuration can be simplified and the configuration can be inexpensive.

According to the second aspect of the invention, the transmission data of a wide range of the subject can be obtained by arranging the detection elements of the main detector and the sub-detector two-dimensionally.

According to the invention described in claim 3, the CT device according to claim 1 is preferably realized.

According to the fourth aspect of the present invention, the central axis of the electromagnetic wave emitted from the irradiating means passes through the center of the region of interest to be imaged and always enters the central point of the main detector. Moreover, since the three-dimensional position of the subject is determined in advance, transmission data of a wide region of interest covered by the main detector can be stably collected.

According to the invention described in claim 5, the central axis of the electromagnetic wave emitted from the irradiating means is imaged while the irradiating means and both detectors are synchronously rotationally scanned around the subject. A rotational movement of the main detector is performed through the center of the region of interest of interest so that it is incident on the center point of the main detector.
That is, the transmission data of the eccentric region of interest of the subject placed in the gantry opening is stably collected by the main detector.

According to the invention of claim 6, a set of the irradiation means and both detectors is provided around the rotation center axis of the subject.
A reconstructed image in a wide region in the central axis direction of rotation is obtained by moving the subject relative to each other and causing electromagnetic waves to spirally scan around the subject.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 illustrates an X-ray CT apparatus as an example of an embodiment of the CT apparatus of the present invention. FIG. 1 is a block diagram showing the schematic arrangement of the X-ray CT apparatus according to this embodiment.

The apparatus of this embodiment has an operating section 10 for inputting various information and commands, and an imaging control section 20 for controlling X-ray imaging based on the input information and commands.
The rotation drive unit 30 that operates the imaging unit 40 while being controlled by the imaging control unit 20, the imaging unit 40 that images the region of interest that is the imaging target of the subject M, and the X-ray irradiation of the X-ray tube of the imaging unit 40. An irradiation control unit 50 for controlling the table, a table driving unit 60 for moving the table, a gantry tilt driving unit 70 for inclining the rotating ring of the image capturing unit 40, and an image capturing unit 40.
A data acquisition unit (D) that converts the X-ray detection signal of the X-ray transmission image detected from the image signal into a digital signal and collects it as image information.
AS) 80, a data processing unit 90 that reconstructs an image of the region of interest of the subject based on the digital signal output from the data collection unit 80, and stores the reconstructed image information, and the data processing unit 90. And a monitor 100 for outputting and displaying the image information stored in 90.

The configuration and function of each unit will be specifically described below. FIG. 2 is a schematic plan view showing one scanning mode of the X-ray tube 41 and the X-ray detector 42 (42A, 42B) in the X-ray CT apparatus of this embodiment. That is, as shown in FIG. 2, the X-ray tube 41 and the X-ray detector 42 are provided around the rotation center axis O which is set substantially at the center of the reconstruction field V of the subject M with the subject M sandwiched therebetween. The object M is relatively rotated and moved, and the X-ray is scanned around the subject M once to take an image. As a result, a transmission image of the subject M about one rotation around the body axis is acquired.

From the operation unit 10, before photographing the reconstructed visual field V of the subject M, the distance from the X-ray tube 41 to the X-ray detector 42, the X-ray tube 41 and the X-ray detector 42 are circular. And the movement pitch in the circular direction of the object M
The position and the like are preset and input. In addition, this operation unit 1
As 0, an input device such as a keyboard, a mouse or a touch panel is used. The X-ray tube 41 corresponds to the irradiation means in this invention.

The photographing control unit 20 includes an operation unit 10, a rotation driving unit 30, an irradiation control unit 50, a top driving unit 60, a gantry tilt driving unit 70, a data processing unit 90, and a monitor 10.
0 and 0 are connected. Then, the imaging control unit 20 comprehensively controls each of the connected units based on each information set and input from the operation unit 10. The control of each unit will be described later.

As shown in FIG. 2, the rotation driving unit 30 sets the X-ray tube 41 and the X-ray detector 42 (42A, 42B), which are opposed to each other with the subject M in between, in the reconstructed field of view of the subject M. The scanning is performed while relatively rotating and moving around the rotation center axis O set at the substantially center of V. At this time, the central axis of the cone-beam-shaped X-rays emitted from the X-ray tube 41 toward the subject M passes through the center O of the reconstructed field of view V aligned with the central position of the region of interest, and passes through the X-ray detector. The X-ray tube 41 and the X-ray tube 41 are arranged so as to be vertically incident on the center point F of the detection surface of
It faces the line detector 42. The rotation drive unit 3
0 corresponds to the first drive means in this invention.

Next, the image pickup section 40 having the characteristic structure of the apparatus of this embodiment will be described. The imaging unit 40 is shown in FIG.
Further, as shown in FIG. 2, an X-ray tube 41 that irradiates the subject M with cone-beam-shaped X-rays, and an X-ray detector 42 (42A, 42A 42
B) is configured to relatively rotate around the subject M placed on the top plate T. In addition, the imaging unit 40
It is provided in the gantry 43.

That is, the image pickup unit 40 has a ring rotating mechanism 45 consisting of a rotating ring 44 to which an X-ray tube 41 and an X-ray detector 42 are fixed, and a pulley 45a and a belt 45b.
And the X-ray tube 41 and the X-ray detectors 42 (42a, 42a, 42a
and b) relatively rotate around the subject M. The rotation movement is controlled by the rotation drive unit 30 by an output signal from the photographing control unit 20 corresponding to the control means of the present invention.

The X-ray detector 42 is a flat panel type X-ray detector 42A (hereinafter referred to as "main detector 42A" as appropriate) and a sub-detector before and after the main detector 42A in the rotating direction. The multi-channel X-ray detector 42B (hereinafter appropriately referred to as "sub-detector 42B") is integrally formed.

Although not shown, the X-ray detector 42A is a two-dimensional matrix X-ray detector in which a large number of detection elements are arranged vertically and horizontally. The X-ray transmission image is detected, converted into an electric signal as an X-ray detection signal, and output. This detection element has, for example, a size of 160 μm.
And a square lattice of 1024 in the horizontal direction and 1024 in the vertical direction.

As shown in FIG. 4, the sub-detector 42B moves away from the main detector 42A, that is, the X-ray detectors 42 (42A, 42A) indicated by arrows RA and RB.
The size of the detection element increases as it goes in the direction of rotation B). In addition, the sub detector 42
As shown in FIG. 2, B is sized to detect X-rays having a spread corresponding to the gantry opening G, and an X-ray transmission image of the subject M generated by X-ray irradiation by the X-ray tube 41. Is detected and converted into an electric signal as an X-ray detection signal for output.

That is, the transmission data as an electric signal of the X-ray transmission image detected by the sub-detector 42B requires the accuracy for outputting the reconstructed image of the subject M detected by the detector 42B. Main detector 42A
It is acquired in order to complement the transmission data of the reconstructed visual field V used for the reconstructed image output from. Therefore, the number of transmission data from the sub-detector 42B can be calculated by the complementing process during the convolution process.
It is sufficient that the false image does not occur in the output image portion of.

Next, the structure of the detection element of the sub-detector 42B will be specifically described. As the arrangement and density of the detection elements in the sub-detector 42B, for example, adjustment of the detection element size can be mentioned. The determination of the detection element size in this case is related to the distance from the main detector 42A and the function value of the convolution processing. That is, as shown in FIG.
The amount of change in the convolution function value CV is determined by the main detector 4
It depends on 1/3 of the distance r from 2A.
That is, the distance pitch at which the amount of change in the convolution function CV becomes constant is conversely the distance r from the main detector 42A.
It is proportional to the cube of.

For example, the range (diameter) of the reconstruction visual field is 240
mm, and when detecting an X-ray transmission image having a spread that covers this reconstructed field of view on the entire surface of the main detector 42A,
As shown in FIG. 6, a range (area E0) of 20 mm from the main detector 42A has the same size as the main detector 42A (160 μm).
The detector elements of m) are arranged two-dimensionally. Then, an area E1 that is sequentially moved away from the area E0 in which the detection elements are arranged,
For E2, E3, E4 ..., The detection elements can be arranged so that the sizes of the detection elements are 1 mm, 8 mm, 27 mm, 64 mm.

The reason why the density and size of the detection elements in the area E0 are set to be the same as those of the main detector 42A in FIG. 6 is that when the convolution profile is created and the reconstructed image is output, This is because it is preferable to maintain the accuracy of the output image that corresponds to the boundary portion of V.

The arrangement and density of the detection elements of the sub detector 42B are not limited to this form.

Next, the irradiation controller 50 includes a high voltage generator and the like, and the imaging controller controls the X-ray tube 41 from the X-ray tube 41 to the subject M according to the set irradiation conditions such as the tube voltage and the tube current. It is configured to irradiate a line.

As shown in FIG. 3, the top plate drive unit 60 is configured to adjust the three-dimensional position within the gantry opening G while the top plate T holds the subject M. That is, the top plate driving unit 60, based on the command signal sent from the imaging control unit 20 according to the input information from the operation unit 10, radiates the X-ray tube 41 from the X-ray tube 41 toward the subject M. Within the gantry opening G, the center axis of the line passes through the center O of the reconstruction field of view V aligned with the center position of the region of interest and is incident perpendicularly on the center point F of the detection surface of the X-ray detector 42. The subject M is moved in advance to a predetermined position.

The gantry tilt drive unit 70 includes the rotary ring 4
4 has an inclination angle, and the irradiation angle of the cone-beam-shaped X-rays from the X-ray tube 41 that irradiates the subject M is changed.

Next, the data collecting section 80 determines that both detectors 42
The transmission data of the X-ray transmission images detected by A and 42B are digitally converted and sent to the data processing unit 90.

The data processing unit 90 further includes a convolution profile creating unit 91 (hereinafter, appropriately referred to as “CVP creating unit 91”), a reconstruction processing unit 92, and an image storage unit 93.

The CVP creating unit 91 reconstructs an image of the region of interest that matches the reconstructed field of view V based on the transmission data from the main detector 42A and the sub-detector 42B sent from the data collecting unit 80. A convolution profile (hereinafter, referred to as “CVP” as appropriate) for creating the convolution profile is created. Note that this creation method will be described later.

The reconstruction processor 92 is adapted to reconstruct an image based on the profile obtained by the CVP generator 91.

The image storage section 93 is adapted to successively store the reconstructed images created by the reconstruction processing section 92.
The stored image data is read by the operator at an appropriate time and displayed on the monitor 100.

The monitor 19 displays an X-ray CT image on the screen when the imaging system is driven in the CT imaging mode, and an X-ray transmission image when driven in the transmission imaging mode. Further, the operator can appropriately switch and display various kinds of information by operating the operation console 17 or the mouse 18 which is an input means.

Next, the procedure for obtaining the reconstructed image of the reconstructed field of view V using the apparatus of the above embodiment will be described.
The operator operates the operation unit 10 to reconstruct a visual field in which the central axis of the cone-beam-shaped X-rays emitted from the X-ray tube 41 is aligned with the central position of the region of interest of the subject M placed on the top plate T. The top plate T is moved and adjusted so as to pass through the center O of V and to be constantly detected at the center point F of the detection surface of the main detector 42A, and CT imaging is executed.

At this time, the transmission data obtained from the X-ray detector 42 including the main detector 42A and the sub-detector 42B shown in FIG. 6a is as shown in FIG. 6b. That is, a large number of detailed data are obtained from the main detector 42A and the sub-detector 42B having the same size of the detection element as the main detector 42A, as indicated by the ● marks.

Further, the transmission data obtained from the portion of the sub-detector 42B where the size of the detection element becomes large is smaller than the number of data indicated by the circle as shown by the circle.

Here, complementary processing is performed to obtain complementary data so that the transmission data obtained from the sub-detector 42B becomes the same as the number of data obtained with the size of the detection element of the main detector 42A. That is, the portion indicated by a triangle in FIG. 6 is obtained as complementary data.

Then, the main detector 42A after the complementary processing is performed.
And the transmission data of the sub-detector 42B, the function used for the convolution processing shown in FIG. 6c is obtained. A CVP of the reconstructed field of view V is created in order to reconstruct and output as an image from the obtained function. That is, the CVP shown in FIG. 6d is created.

An image of the reconstruction visual field V is reconstructed by the reconstruction processing unit 92 based on the CVP obtained by the above-mentioned procedure in the CVP creating unit 91, and is stored in the image storage unit 93.

As described above, by providing the sub-detectors 42B before and after the main detector 42A in the rotation direction, the reconstructed field of view V in the conventional apparatus during convolution processing.
As a result, the transmission data of the portion that runs off and is lacking is replenished. As a result, it is possible to prevent a false image caused by the lack of transmission data, and it is possible to substantially obtain an image having a wider reconstruction field of view than the conventional device. .

Further, since the size and density of the detection elements of the sub-detector 42B can be made larger (size) or smaller (density) than that of the main detector 42A, the structure can be simplified. At the same time, it can be made inexpensive.

<Second Embodiment> An X-ray CT apparatus according to the second embodiment will be described with reference to the drawings. In the device of the second embodiment, the parts different from those of the first embodiment will be described, and common parts will be denoted by the same reference numerals and description thereof will be omitted.

In the X-ray CT apparatus of this embodiment, as shown in FIG. 7, the main detector 42A and the main detector 42A are arranged in the rotation direction of the main detector 42A so that the back of the main detector 42A is covered with the main detector 42A. It has a horizontally long sub-detector 42B.

The main detector 42A is a flat panel X-ray detector of a two-dimensional matrix in which a large number of detection elements are arranged vertically and horizontally, and the X-ray of the subject M generated by the X-ray irradiation by the X-ray tube 41. The X-ray transmission image is detected, converted into an electric signal as an X-ray detection signal, and output. The array of the detection elements has, for example, an element size of 160 μm.
An example is a square matrix in which the horizontal direction is 1024 and the vertical direction is 1024.

As shown in FIG. 8, the main detector 42A is provided with a slide mechanism 46, and the gantry 43 is controlled by controlling the main detector drive unit 33 according to the signal sent from the photographing control unit 20. It is adapted to move on a guide rail 47 provided in a circular shape inside. That is, the main detector 42A and the sub-detector 42B are configured to be independently driven. In particular, the main detector 42A is configured to be displaced within the widthwise direction (rotational movement direction) of the sub-detector 42B during scanning.

That is, as shown in FIG. 7, the reconstructed field of view in which the central axis of the cone-beam-shaped X-rays emitted from the X-ray tube 41 toward the subject M during scanning is aligned with the central position of the region of interest. The main detector 42A is displaced before and after being within the range covered by the sub-detector 42B so as to pass through the center O of V and always vertically enter the center point F of the detection surface of the main detector 42A. At this time, the X-ray tube 41 and the sub-detector 42B are synchronized with each other, and rotate and move while facing each other. The main detector drive unit 33 corresponds to the third drive means of the present invention.

Next, the sub detector 42B is connected to the main detector 42.
Similar to A, this is a two-dimensional matrix multi-channel X-ray detector in which a large number of detection elements are arranged vertically and horizontally. For the arrangement of the detection elements of the sub-detector 42B, a square or vertically long element having an element size of 1.0 to 64 mm is selected and used in a timely manner.

The size of the sub-detector 42B is preferably such that it can detect transmitted X-rays having a spread corresponding to the gantry opening G.

Next, the procedure for obtaining the reconstructed image of the reconstructed field of view V using the apparatus of the above-described embodiment will be described with reference to FIG. Based on the transmission data of the X-ray detection signal detected by the detector 42A and the X-ray detection signal detected by the sub-detector 42B excluding the portion where the X-ray is shielded by the main detector 42A (hatched portion in FIG. 7). Transparent data is the data processing unit 9
Input to 0. The CVP creation unit 91 creates a CVP for the reconstruction visual field V based on the input transmission data.

After the CVP is created, the reconstructed image of the region of interest that matches the reconstructed field of view V is created by the reconstruction processing unit 92 and stored in the image storage unit 93 by the same method as in the previous embodiments.

<Third Embodiment> An X-ray CT apparatus according to the third embodiment will be described with reference to the drawings. In the device of the third embodiment, parts different from those of the first embodiment will be described, and common parts will be denoted by the same reference numerals and description thereof will be omitted.

In the X-ray CT apparatus of this embodiment, as shown in FIG. 10, a sub-detector 42B which is horizontally long in the rotational direction of the X-ray detector 42A is arranged in front of the main detector 42A.

The sub-detector 42B is filled with xenon gas (Xe) inside and is constituted by an ionization chamber having electrodes arranged in a two-dimensional matrix. The pitch between the electrodes is determined by the main detector 42.
It is wider than the pitch of the A detection element and larger than the size of the detection element of the main detector 42A. Further, the sub-detector 42B detects a part of the X-rays that have passed through the subject M and allows the rest of the X-rays to pass therethrough. The X-ray detection efficiency of the sub-detector 42B is, for example, one that is 1% or less of transmitted X-rays.

The size of the sub-detector 42B is
It is preferable that the transmitted X-rays having a spread corresponding to the gantry opening G are detected.

Then, the main detector 42A and the sub-detector 42
B is a cone-beam-shaped X emitted from the X-ray tube 41.
Rotate so that the central axis of the line passes through the center O of the reconstructed field of view V aligned with the center position of the region of interest and the X-rays are detected by being incident perpendicularly on the central point F of the detection surface of the main detector 42A. The driving unit 30 causes the X-ray tube 41 to rotate together. The main detector 42A and the sub-detector 42B may be moved by rotating the main detector 42A and 42B while fixing the positions of the two detectors 42A and 42B.
The main detector 42A may be displaced in the width direction of 2B.

Next, a procedure for obtaining a reconstructed image of the reconstructed field of view V using the apparatus of the above-mentioned embodiment will be described.
The transmission data based on the X-ray detection signal obtained from the embodiment apparatus having the above-described configuration is input to the data processing unit 90 via the data collection unit 80. Based on the input data, the CVP creation unit 91 creates a CVP for the reconstruction visual field V.

The CVP is created by, for example, the sub-detector 42.
The portion of the transmission data detected in B that overlaps with the transmission data obtained by the main detector 42A is not used, but the transmission data of the remaining portion and the transmission data of the main detector 42A are used. . The method for creating the CVP in this embodiment is not limited to this mode.

After the CVP is created, the reconstructed image of the reconstructed field of view V is created by the reconstruction processing unit 92 and stored in the image storage unit 93 by the same method as in the previous embodiments.

The present invention is not limited to the above embodiment, but can be modified as follows. (1) In each of the above-described embodiments, the X-ray tube 41 and both detectors 42A and 42B are rotationally moved around the subject M so that the X-ray scans around the subject M. The present invention is not limited to this embodiment. For example, as shown in FIG. 11, the mounting table on which the inspection target M1 is mounted may be rotated. That is, it can be suitably used for nondestructive measurement.

(2) In each of the above-described embodiments, the X-ray detector 41 and both detectors 42A are provided around the rotation center axis of the subject M.
Although 42B was rotationally moved, the present invention is not limited to this configuration. For example, a set of an X-ray tube 41 and both detectors 42A and 42B so that X-rays spirally scan around the subject M, It may have a configuration in which the subject M is relatively rotated.

During scanning, the central axis of the cone-beam-shaped X-rays emitted from the X-ray tube 41 is the center of the reconstructed field of view V, that is, the subject placed on the top plate T along with the spiral scanning. It is designed to be detected perpendicularly to the center point of the detection surface of the main detector 42A through the central axis of the reconstruction field of view that extends in the moving direction of M.

(3) In each of the above-described embodiments, the detection elements of the sub-detector 42B are two-dimensionally arranged so as to be adjacent to each other. However, the present invention is not limited to this configuration, and the sub-detectors 42B are not adjacent to each other at a predetermined interval. The detection elements may be arranged one-dimensionally or two-dimensionally (for example, refer to the portion 42B in FIG. 4).

(4) In the apparatus of each of the above embodiments, the X-ray tube 41
The center axis of the cone-beam-shaped X-ray emitted from the laser beam passes through the center O of the reconstruction field of view V aligned with the center position of the region of interest and is detected perpendicularly to the center point F of the detection surface of the main detector 42A. Although the scanning is performed as described above, the present invention is not limited to this form, and the X-ray tube 41 and both detectors 42 are simply centered around the gantry 43.
A and 42B may be configured to move so as to face each other around the subject M, and the center O of the reconstructed visual field V and the position of the center of the region of interest may not necessarily be aligned. .

[0076]

As is apparent from the above description, according to the first aspect of the present invention, by providing the sub-detector, the convolution process is executed using the transmission data detected only by the main detector. The error of the CVP that occurs at this time can be repaired by using the transmission data of the area outside the reconstruction field of view. That is, it is possible to prevent the generation of a false image and to output a reconstructed image in a range wider than the reconstructed field of view of the conventional apparatus.

Further, since the density of the detection elements of the sub-detector is smaller than that of the main detector, the structure can be simplified and the cost can be reduced.

According to the second aspect of the invention, the transmission data of a wide range of the object can be obtained by arranging the detection elements of the main detector and the sub-detector two-dimensionally.

Further, according to the invention described in claim 3, by arranging the density of the detection elements of the sub-detector so as to increase as the distance from the boundary line of the reconstruction field of view increases,
The CT device according to the first aspect can be suitably realized.

Further, according to the invention described in claim 4, during the rotational scanning of the irradiation means and both detectors around the subject synchronously, the central axis of the electromagnetic wave emitted from the irradiation means is imaged. Stable transmission data of the region of interest covered by the main detector by predetermining the three-dimensional position of the subject so that it always enters the center point of the main detector through the center of the region of interest. Therefore, it is possible to further prevent the generation of false images.

According to the fifth aspect of the invention, the central axis of the electromagnetic wave emitted from the irradiating means is imaged while the irradiating means and both detectors are rotationally scanned in synchronization around the subject. By displacing the main detector through the center of the region of interest to be incident on the center point of the main detector, the transmission data of the eccentric region of interest of the subject placed at the gantry aperture is stabilized. Can be collected by
It is possible to further prevent the generation of false images.

According to the invention described in claim 6, reconstructed image data of a wide region of interest can be obtained by executing spiral scanning.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an X-ray CT apparatus according to a first embodiment.

FIG. 2 is a schematic plan view showing a scanning mode of the X-ray CT apparatus according to the first embodiment.

FIG. 3 is a schematic diagram showing movement of a top plate.

FIG. 4 is a configuration diagram showing an arrangement of detection elements of a sub-detector.

FIG. 5 is a schematic diagram for determining the size of a detection element of a sub detector.

6A and 6B are schematic diagrams when creating a convolution profile (CVP), including (a) a diagram of a detector used for profile processing, and (b) a sub-detector based on data detected by both detectors. FIG. 6 is a diagram showing a data distribution when the data in FIG. (D) It is a figure which shows CVP calculated | required by arithmetic processing.

FIG. 7 is a schematic plan view showing a scanning mode of the X-ray CT apparatus according to the second embodiment.

FIG. 8 is a schematic diagram showing movement of a main detector.

FIG. 9 is a diagram showing an X-ray detection state.

FIG. 10 is a diagram showing an arrangement of both detectors and an X-ray detection state of the third embodiment.

FIG. 11 is a perspective view showing a scanning mode of an X-ray CT apparatus according to a modified example.

FIG. 12 is a schematic plan view showing a main configuration of an X-ray CT apparatus of a conventional example.

[Explanation of symbols]

G ... Gantry aperture M ... Subject T ... Top plate V ... Reconstruction field of view 10 ... Operation unit 20 ... Imaging control unit 30 ... Rotation drive unit 41 ... X-ray tube 42 ... X-ray detector 42A ... Main detector 42B ... Sub Detector 70 ... Top drive unit 90 ... Data processing unit 91 ... CVP creation unit (convolution profile) 92 ... Reconstruction processing unit 93 ... Image storage unit

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2G001 AA01 BA11 CA01 DA02 DA06                       DA09 HA01 HA08 HA13 KA03                       LA01 PA12                 4C093 AA22 BA03 BA08 BA10 CA13                       CA29 CA32 EA02 EB17 EC48                       FA22 FA42 FD07

Claims (6)

[Claims] 1. An irradiation means (a) for irradiating a subject placed on a top plate in the shape of a divergent beam toward a subject, and (b) facing the subject with the subject in between. A detection means arranged and provided with a plurality of detection elements for detecting electromagnetic waves transmitted through the subject; and (c) the irradiation means and the detection means so that the electromagnetic waves scan around the subject. In a CT apparatus including a first driving unit that relatively rotationally moves around the subject, the detection unit includes (d) a main detector that detects a broad electromagnetic wave that covers a reconstructed field of view. And (e) a sub-detector for detecting electromagnetic waves that have passed through the main detector and transmitted, and the density of the detection elements of the sub-detector is smaller than that of the main detector. apparatus. 2. The CT apparatus according to claim 1, wherein
(F) A CT device in which each detection element of the main detector and the sub-detector is two-dimensionally arranged. 3. The CT apparatus according to claim 1 or 2, wherein (g) the density of the detection elements of the sub-detector decreases as the distance from the boundary line of the reconstruction field of view of the main detector increases. A CT device characterized by being arranged. 4. The CT apparatus according to claim 1, wherein (h) the irradiation means and the detection means are relatively rotated around the subject,
The three-dimensional position of the subject is adjusted in advance so that the central axis of the electromagnetic wave emitted from the irradiation means passes through the center of the region of interest, which is the imaging target, and is incident on the center point of the detection surface of the main detector. A CT apparatus comprising two driving means. 5. The CT apparatus according to any one of claims 1 to 3, wherein (i) the irradiation means and the detection means are relatively rotationally moved around the subject,
A third drive unit is provided for displacing the main detector so that the central axis of the electromagnetic wave emitted from the irradiation unit passes through the center of the region of interest, which is the imaging target, and is incident on the center point of the detection surface of the main detector. A CT device characterized in that 6. The CT apparatus according to claim 1, wherein (j) the set of the irradiation unit and the detection unit and the subject are moved relatively to each other, and the electromagnetic wave is generated. Is provided with control means for controlling the first driving means so as to spirally scan around the subject.