JPH07124147A - Radiation computed tomography equipment - Google Patents

Abstract

(57) [Abstract] [Purpose] The slice thickness is reduced by narrowing the beam thickness of the radiation fan beam that irradiates multiple detectors and reducing the slice interval. To provide an X-ray CT apparatus capable of obtaining a tomographic image. Constitution: A means 10 for irradiating a radiation fan beam F _x toward a subject P, and a means 10 for radiating the radiation fan beam F _x , which are opposed to each other with the radiation generation means 10 interposed therebetween, respectively.
Of a plurality of radiation detecting elements arranged in a one-dimensional array along the spreading direction of the slices, the intervals of the slices can be changed according to the width of the slices, and the projection data of a plurality of slices 31 to 31 can be simultaneously acquired. 33 and means 20 for providing a beam thickness in the direction perpendicular to the divergence direction of the radiation fan beam F _x .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to radiation computed tomography for obtaining multi-directional projection data of a subject by helical scanning and reconstructing the multi-directional projection data to obtain a tomographic image of the subject. The present invention relates to an apparatus (hereinafter referred to as “radiation CT apparatus”), and more particularly to a radiation CT apparatus capable of obtaining a precise tomographic image in a short time by providing a plurality of rows of detectors.

[0002]

2. Description of the Related Art In an X-ray CT apparatus, which is one of conventional radiation CT apparatuses, an X-ray tube and a detection element are arranged along a spreading direction of an X-ray fan beam emitted from the X-ray tube. The multi-channel type one-dimensional array detector is continuously rotated together with the subject placed on the bed, and the bed is sent to collect projection data, and the projection data is reconstructed to obtain a plurality of data. A helical scan is used that can obtain a tomographic image in a short time. In an X-ray CT apparatus that performs such a helical scan, when obtaining a tomographic image of a required slice plane, it is generally performed by interpolation from projection data for two rotations in the front and rear. 2 used to reconstruct one such cross-sectional image
The range of data for rotation is called the data range.

An X-ray CT for performing a helical scan
In the apparatus, it is desirable to end the scan in a short time in order to prevent the tomographic image from being shaken by the body movement of the subject during the scan. Therefore, the X-ray tube and the detector are rotated at high speed, and the amount of the bed to be sent within a unit time is increased.

[0004]

However, when data is collected by helical scanning in the conventional X-ray CT apparatus as described above, there are the following problems. That is, when the bed feeding speed is increased, the data range becomes wider, and when the required slice plane projection data is interpolated, there is a problem that projection data at a position distant from the slice plane must be adopted. High-quality tomographic images could not be obtained.

Therefore, it is considered that detectors are provided in a plurality of columns in parallel in the bed feeding direction so that interpolation can be performed from projection data at the same bed feeding speed and closer positions.
Here, assuming that the detector has n rows, the slice row pitch is p, and the bed feed pitch is d, the data range D is D = d−p · (n−1) (1) Therefore, when collecting data by helical scanning, it is possible to interpolate from data closer to the slice plane to be reconstructed by providing many detectors, and a high-quality tomographic image can be obtained.

On the other hand, the range of the data actually used to obtain the data of the slice plane tomographic image is actually called the effective slice thickness D'in consideration of the width of the detector. FIG. 5 is a diagram for explaining a data range D and an actual slice thickness D ′ for obtaining a tomographic image of a slice plane A in an X-ray CT apparatus equipped with three rows of detectors. It is the figure seen from. The detector has one-dimensionally arranged X-ray detection elements in the vertical direction in the figure. Here, T is the X-ray irradiation range by the X-ray tube, S _{1 to} S ₃ are the detection ranges of the detector, and α is the gap in the beam thickness direction of the X-ray fan beam. Furthermore, when the beam thickness of the X-ray fan beam is t, the thickness of the data actually used to obtain the data of the tomographic image of the slice plane A, that is, the execution slice thickness D ′ is at both ends of the data range D. Half the beam thickness t / 2
And the execution slice thickness D ′ is D ′ = D + t = d−p · (n−1) + t (2) As the execution slice thickness D'is thinner, a high-quality tomographic image of the slice plane A can be obtained.

By the way, in order to reduce the effective slice thickness D'without changing the interval between the detectors, that is, the slice row pitch p, the bed feeding pitch d should be reduced and the beam thickness t should be narrowed. It can be seen from equation (2). Therefore, in the X-ray CT apparatus equipped with the detectors of n rows, if the bed feeding pitch d = p · n is set so that the range of β in FIG. 5 is as small as possible, the data as shown in FIG. The range D has a minimum value of d / n. Therefore, the execution slice thickness D'is D '= d / n + t.

On the other hand, when scanning a head that requires a more precise tomographic image than the abdomen and chest, the beam thickness t is determined by narrowing the X-ray fan beam F _x with a diaphragm mechanism. Need to be thin. However, assuming that the normal beam thickness is t ₁ and the beam thickness after narrowing is t ₂ , the slice row pitch p, that is, the distance between the detector center lines is fixed, and therefore the data range D does not change. Therefore, as shown in FIG. 6, although the X-ray fan beam is narrowed to reduce the beam thickness with respect to the normal execution slice thickness D ′ = d / n + t ₁ , the execution slice thickness D ″ after the reduction is reduced. = d / n + t _2, and the beam thickness does not become only thinned min run slice thickness is thin. Therefore, there is a problem that it is difficult to obtain a tomographic image of high quality. the beam cross Is α ′, which is wider than the normal interval α between the beams.

Therefore, the present invention provides a plurality of multi-channel type 1
As the X-ray fan beam irradiating the two-dimensional array detector is narrowed to reduce the beam thickness, the slice interval is reduced to reduce the execution slice thickness, and a high-quality tomographic image is obtained from the precise acquired data. Available X-ray CT
The purpose is to provide a device.

[0010]

In order to solve the above problems and achieve the object, the present invention provides a means for irradiating a subject with a radiation fan beam, and a means for sandwiching the radiation generating means and the subject. Arranged facing each other, each consisting of a plurality of radiation detection elements arranged one-dimensionally along the direction of expansion of the radiation fan beam, the interval of the slice can be changed according to the width of the slice, projection data of a plurality of slices It is provided with a plurality of detecting means capable of collecting at the same time, and means for giving a beam thickness in a direction perpendicular to the diverging direction of the radiation fan beam.

[0011]

As a result of taking the above-mentioned means, the following effects occur. That is, when the width of the slice is reduced by reducing the beam thickness of the radiation fan beam, the interval between the slices can be reduced. Therefore, the data range required for reconstruction of the tomographic image is narrowed, the resolution in the slice direction of the image is improved, and as a result, it becomes possible to obtain a high-quality tomographic image.

[0012]

1 is a block diagram showing the configuration of an X-ray CT apparatus according to an embodiment of the present invention. Further, FIG. 2 is a side view showing the detection unit. The X-ray CT apparatus according to the present embodiment forms an X-ray tube 10 for irradiating X-rays, which is provided on a mount (not shown), and an X-ray fan beam F _x emitted from the X-ray tube 10 into a parallel bundle, and a predetermined amount. Slit device 20 for squeezing to the slice thickness of
The detection unit 30 detects the X-ray intensity of the X-ray fan beam F _x that has passed through the subject P placed on the bed.
A data collecting unit 40 that collects the detected projection data is connected to the detecting unit 30.
Is an image reconstruction unit 50 that reconstructs an image from projection data.
Are connected. A monitor 60 that displays a reconstructed cross-sectional image is connected to the image reconstruction unit 50, and a main control unit 70 that controls the X-ray CT apparatus is connected to the monitor 60 and the image reconstruction unit 50. There is. The operator gives an instruction to the main control unit 70 using a console (not shown).

The slit device 20 includes two slit blades 21 and 22 which are independently movable in the slice thickness direction, that is, in the arrow Q direction in the figure, and these slit blades 21 and 22.
The slit driving units 23 and 24 for driving the slit driving unit 22 and the slit control unit 25 for controlling the slit driving units 23 and 24 are provided. The slit control unit 25 is the main control unit 7.
It is connected to 0. By adjusting the positions of the slit blades 31 and 32, the beam thickness of the X-ray fan beam F _x reaching the detection unit 30 in a direction perpendicular to the diverging direction is adjustable.

The detection unit 30 includes three multi-channel type one-dimensional array detectors 31, 32 and 33 each of which is composed of a large number of detection elements which are arranged one-dimensionally along the spreading direction of the X-ray fan beam F _x. Is provided. Detector 31-
The width of the slice 33 in the slice thickness direction is t ₁ and the thickness thereof is μ. These detectors 31 to 33 are arranged at a slight interval in the thickness direction of the X-ray fan beam F _x , and the detectors 31 and 33 are arranged in the irradiation direction of the X-ray fan beam F _x with respect to the detector 32. It is arranged at a position close to the X-ray tube 10 by a value slightly larger than μ. It should be noted that detection surfaces 31a, 32a, 33a are provided on the X-ray tube 10 side of the detectors 31 to 33 as shown in FIG.
The X-ray shield plate 3 is provided on the surface opposite to the detection surfaces 31a to 33a.
1b, 32b, 33b are provided. Further, the detectors 31 and 33 can be driven in the directions of the arrows R in the figure by the detector driving units 34 and 35, respectively.
4, 35 are controlled by the detector control unit 36. The detector control unit 36 is connected to the main control unit 70.

The X-ray CT apparatus configured as described above operates as follows. That is, normally, the detectors 31 to 33 are at positions where they do not overlap the X-ray fan beam F _x , as shown in FIG. At this time, each detector 31-
The beam thickness applied to 33 is t ₁ . When the operator issues a scan start command, a helical scan is started, the intensity of X-rays emitted from the X-ray tube 10 and transmitted through the subject P is detected by the detector 30, and projection data is collected by the data collector 40. To be done. The collected projection data is reconstructed by the image reconstructing device 50 and displayed on the monitor 60.

On the other hand, when the beam thickness is reduced to obtain a precise tomographic image, the operator specifies the beam thickness. The slit drive unit 23, 24 is controlled by the slit control unit 25 according to the beam thickness, and the slit blade 21,
22 is closed and the beam thickness is reduced.

Further, the detectors 31 and 33 are the detector control unit 3
6, so that the slice row pitch of the detectors 31 to 33 becomes small, the detector drive units 34 and 3 are arranged in accordance with the beam thickness.
Positioning is performed by 5 as shown in FIG. At this time, the detectors 31 and 33 block the detection surface 32a of the detector 32 with respect to the X-ray fan beam F _x , and the beam thickness irradiated to each of the detectors 31 to 33 is t ₂ .

Here, when the operator commands the start of scanning, a helical scan is performed and a tomographic image of the subject P is obtained. According to the present embodiment, by moving the detectors 31 and 33 to the center, it is possible to prevent the distance between the beams from expanding. That is, when collecting the data of the slice plane A, normally, when the beam thickness irradiated to each detector is t ₁ , as shown in FIG. 3, the data range is D ₁ and the execution slice thickness is D ′. Becomes On the other hand, when the beam thickness is thinned to t ₂ , the center interval of each slice approaches, so the data range becomes D ₂ .
The execution slice thickness becomes D ″, and the execution slice thickness can be significantly reduced. Therefore, it is possible to obtain a high-quality tomographic image. Further, the detectors 31 to 33 have X-ray shielding materials 31b. Since .about.33b are attached, the X-ray beam transmitted through the upper detector is not detected by the lower detector.

FIG. 4 shows an X-ray CT according to the second embodiment of the present invention.
It is a side view which shows the slit device and detection part of an apparatus. The configuration of the present embodiment is the same as that of the above-described first embodiment except the configuration of the detection unit, and thus the description thereof is omitted.

In the X-ray CT apparatus of this embodiment, detectors 81 and 82 are arranged side by side in the beam thickness direction in the detector 80. In the X-ray CT apparatus configured as described above, when the beam thickness is reduced, the slit blades 21 and 22 are moved in the arrow direction in the figure. Accordingly, the detectors 81 and 82
The center of the beam of the X-ray fan beam F _x which is irradiated on the beam approaches the connecting portion between the detector 81 and the detector 82. Therefore, as in the first embodiment, it is possible to prevent the distance between the beams from expanding. Therefore, the execution slice thickness is substantially reduced, and it becomes possible to obtain a high-quality tomographic image.

The present invention is not limited to the above embodiments. That is, in the above-described embodiment, the case where the number of detectors is 3 and the case where the number of detectors is 2 have been described. You should try to increase the overlap. Further, although the helical scan has been described as the scanning method, it can be applied to a conventional scan in which the rotation of the X-ray tube and the detector and the feeding of the bed are alternately repeated, particularly the rapid scan. Of course, various modifications can be made without departing from the scope of the present invention.

[0022]

According to the present invention, the radiation beam is moved by moving the central position in the beam thickness direction of these radiation beams according to the beam thickness of the radiation beams with which a plurality of multi-channel type one-dimensional array detectors are irradiated. It is possible to minimize the mutual gap. Therefore, when the radiation beam is narrowed to reduce the beam thickness, it is possible to reduce the effective slice thickness as much as possible. Therefore,
The data range required for reconstruction is narrowed, the resolution in the slice direction of the image is improved, and as a result it is possible to obtain a precise tomographic image.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an X-ray CT apparatus according to a first embodiment of the present invention.

FIG. 2 is a side view showing a detection unit in the device,
(A) shows the case where the beam thickness is not narrowed, and (b) shows the case where the beam thickness is narrowed.

FIG. 3 is an explanatory view showing a change in the execution slice thickness when the beam thickness is changed in the same apparatus.

FIG. 4 is a side view showing the configurations of a slit device and a detection unit of the X-ray CT apparatus according to the second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an execution slice thickness in a helical scan.

FIG. 6 is an explanatory diagram showing an actual slice thickness when the beam thickness is narrowed in FIG.

[Explanation of symbols]

10 ... X-ray tube 20 ... Slit device 21, 22 ... Slit blade 23, 24 ... Slit drive unit 25 ... Slit control unit 30, 80 ... Detection unit 31-33, 81, 82 ... Detector 31a-33a ...
Detecting surfaces 31b to 33b ... X-ray shielding plates 34, 35 ... Detector driving section 36 ... Detector controlling section 40 ... Data collecting section 50 ... Image reconstructing section 60 ... Monitor 70 ... Main controlling section

Claims (4)

[Claims] 1. A means for irradiating a subject with a radiation fan beam and a means for radiating the radiation fan beam and the radiation generating means, which are opposed to each other with the subject in between, each one-dimensionally along a direction in which the radiation fan beam spreads. Consisting of a plurality of radiation detection elements arranged, the interval of the slice can be changed according to the width of the slice, a plurality of detection means capable of simultaneously collecting projection data of a plurality of slices, and the divergence direction of the radiation fan beam And a means for providing a beam thickness in the vertical direction. 2. The radiation computed tomography apparatus according to claim 1, wherein when the number of detecting means is three or more, the means for giving the beam thickness and the movement of the detecting means change the slice interval. . 3. A radiation computed tomography apparatus according to claim 2, wherein a radiation shielding material is provided on the back side of the detection surface of said detection means. 4. The radiation computed tomography apparatus according to claim 1, wherein when the number of detecting means is two, the means for giving the beam thickness changes the slice interval.