JP2000139885A - Radiation projecting image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily form a projecting picture in a radiation projecting image forming device utilizing a focal surface image forming means forming a focal surface image in a scanning beam type radiation image forming device. SOLUTION: This device scans the entire surface of the target surface of a target collimator part 16 by an electron beam L1 and successively radiates an X-ray beam L2 toward a subject 9 from each collimator hole 17. An X-ray L2 transmitted through the subjected 9 is detected by a radiation detecting element and a focal surface image forming means 31 obtains focal surface image data D2 on each of a plurality of focal surfaces existing between a radiating detector 20 and the holes 17. An image conversion processing means 32 gives interpolating processing such as the correction of a magnification, the conversion of pixel density to each focal surface picture to adjust the position of pixels. A projecting image forming means 33 adds pixel values at the same pixel position of each focal surface image to each other to form the projecting image of the subject 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation projection image forming apparatus, that is, an apparatus for forming a radiation projection image of a subject, and more particularly, to radiation emitted sequentially from a plurality of radiation sources arranged on a surface. The present invention relates to a radiation projection image forming apparatus using focal plane image forming means for detecting subject transmission information by a plurality of radiation detecting elements and forming a focal plane image at a predetermined focal plane in a subject.

[0002]

2. Description of the Related Art In the field of medical images, X-ray CT or MRI for obtaining an image relating to a certain cross section of a subject, that is, a cross-sectional image, or an apparatus for continuously obtaining a cross-sectional image has been widely used. The accuracy of has been dramatically improved.

An apparatus for acquiring this cross-sectional image forms radiation emitted from a radiation source in a fan beam shape, irradiates the fan beam-shaped radiation to a subject, and forms a linear beam arranged corresponding to the fan beam. While detecting the radiation transmitted through the subject by the radiation detector, the radiation source and the radiation detector are rotated around the subject by one rotation relative to the subject to obtain a cross-sectional image in the plane of the rotation orbit. Is common.

On the other hand, in contrast to this, a plurality of radiation detecting elements detect transmitted radiation information from radiation sequentially radiated to a subject from a large number of radiation sources arranged on a plane, and a predetermined focal plane in the subject is detected. (Hereinafter referred to as a “scanning beam type radiation image forming apparatus”) for acquiring a focal plane image (tomographic image) in the field has been proposed (SPIE VOL.2708P1).
40-P149, see Japanese Patent Application Laid-Open No. 8-508431).

[0005] At present, research on technologies for detecting three-dimensional radiation image information has been conducted, and for example, helical CT and cone beam CT have been proposed ("Current state of cone beam CT development and its future"). Video information (M); 19
Jan. 1988, P122 to P127, JP-A-9-25307
No. 9).

Here, "cone beam CT" refers to a transmitted radiation image at each rotational position detected by the radiation detector while irradiating radiation while rotating a radiation source and a two-dimensional radiation detector around a subject. (Detailed projection image)
Is used to acquire three-dimensional radiation image information (volume data).

Further, the present applicant utilizes the radiation source and one or a plurality of radiation detecting elements used in the above-described scanning beam type radiation image forming apparatus to transmit two-dimensional transmitted radiation in a number of projection directions of a subject. There has been proposed a radiation image detecting apparatus which sequentially obtains images and obtains volume data of a subject based on the transmitted radiation image, thereby obtaining volume data which is not affected by scattered radiation (Japanese Patent Application No. 2002-214,197). Hei 10-238737).

A device for acquiring volume data, such as a helical CT, a cone beam CT, or a device disclosed in Japanese Patent Application No. Hei 10-238737, is hereinafter referred to as a “three-dimensional CT”.
That.

[0009]

By the way, in the above-mentioned scanning beam type radiation image forming apparatus, a focal plane image at a predetermined focal plane in a subject is obtained based on each transmitted radiation image information detected by a plurality of radiation detecting elements. The position of this focal plane depends on the number and arrangement pitch of the radiation detecting elements and point sources, and the distance between the radiation detector and the radiation source. As long as the relative position with respect to the system is not moved, it is not possible to form a tomographic image in an arbitrary cross section as in three-dimensional CT.

The purpose of this scanning beam type radiation image forming apparatus is to obtain a tomographic image as described above, and it is not possible to obtain a projection image immediately. Of course, based on each transmitted radiation image information detected by a plurality of radiation detection elements, a projection image can be obtained independently of each other. Therefore, it is conceivable to collect these to form one projection image. At present, the algorithm for that purpose has not been fully established yet.

The present invention has been made in view of the above circumstances, and a plurality of radiation detecting elements detect subject transmission information due to radiation sequentially radiated from a large number of radiation sources arranged on a surface, and the predetermined It is an object of the present invention to enable a projection image to be easily formed in a radiation projection image forming apparatus using a focal plane image forming means for forming a focal plane image on a focal plane.

It is another object of the present invention to form a three-dimensional image using the projection image.

[0013]

SUMMARY OF THE INVENTION A radiation projection imaging apparatus according to the present invention has a number of sources arranged on a surface,
A radiation source for irradiating a subject with radiation while sequentially switching each of the radiation sources, a radiation detecting unit including a plurality of detection elements arranged to detect radiation emitted from each of the multiple sources and transmitted through the subject, A focal plane image forming means for forming a focal plane image on a plurality of focal planes between the radiation source and the radiation detecting means based on the output signal of the element; And a projection image forming means for forming a projection image of the subject based on the image data.

Further, the focal plane image forming means of the radiation projection image forming apparatus according to the present invention performs weighting correction according to each line length of the radiation when the detecting element detects the radiation, and outputs each output signal of the detecting element. It is desirable to form a focal plane image by adding.

Here, "weighting correction according to each line length"
Any method may be used as long as it is a correction aiming at eliminating an influence caused by a difference in X-ray intensity due to a difference in line length.

Further, the radiation projection image forming apparatus according to the present invention enlarges each of the plurality of focal plane images in a direction in which the focal plane extends (focal plane direction) or in a direction connecting the radiation source and the radiation detecting means. The image processing apparatus further includes image conversion processing means for performing rate correction and pixel density conversion, and performing image conversion processing such as density adjustment and contrast adjustment and response adjustment on a plurality of focal plane images. It is preferable that the forming means forms a projection image based on the processed focal plane image subjected to the image conversion processing.

Further, the radiation projection image forming apparatus according to the present invention comprises: a rotation means for rotating a radiation source and a radiation detection means around an object relative to the object to change a projection direction of radiation to the object; It can be a so-called three-dimensional CT including three-dimensional image forming means for forming a three-dimensional image of the subject based on projection images in a plurality of different projection directions with respect to the subject.

[0018]

According to the radiation projection image forming apparatus of the present invention, a projection image of a subject is formed based on a plurality of focal plane images by, for example, adding the focal plane images. One projection image can be formed.

Further, if the focal plane image is formed by performing weighting according to each line length of the radiation, it is possible to eliminate the influence caused by the difference in the X-ray intensity due to the difference in the line length. An appropriate focal plane image can be formed, and a more appropriate projected image can be formed.

Further, each focal plane image is subjected to image conversion processing such as correction processing such as enlargement ratio correction, gradation processing and response adjustment, and based on the processed focal plane image subjected to this image conversion processing. If a projection image is formed by using this method, a more appropriate projection image can be formed.

Furthermore, the radiation source and the radiation detection means are rotated around the subject relative to the subject, and projection images are formed in a plurality of different projection directions, respectively, based on the plurality of projection images. 3
Since a three-dimensional image can be formed, an easy-to-use three-dimensional CT apparatus can be configured similarly to the conventional cone beam CT.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a radiation projection image forming apparatus according to an embodiment of the present invention.

As shown in FIG. 1, the radiation projection image forming apparatus 1 includes a radiation source 10, a radiation detector 20, an A / D converter 30 for digitizing an output signal S of the radiation detector 20, Focal plane image forming means 31 for forming a focal plane image on a focal plane (details will be described later) based on the transmitted radiation image carried by the digitized image signal D1
Image conversion processing means 32 for performing various image conversion processing such as magnification correction on the focal plane image, and projection image forming means 33 for forming a projection image based on the focal plane image subjected to the image conversion processing And 3 of the subject 9 based on the projection image.
Dimensional radiation image information (reconstructed 3D image information;
Volume data).

The radiation projection image forming apparatus 1 is provided with a rotation unit (not shown) for rotating the radiation source 10 and the radiation detector 20 around the subject 9 relative to the subject 9. . This rotation means includes a radiation source 1
The radiation source 10 and the radiation detector 20 may be rotated around the line indicated by ZZ ′ in the drawing that passes through the subject 9 while maintaining the relative position between the radiation source 10 and the radiation detector 20. , The radiation source 10 and the radiation detector 20 are fixed, and the object 9
May be rotated.

The three-dimensional image forming means 40 reconstructs a data collection subsystem 41 for collecting the projection image data D4 from the projection image forming means 33, a frame buffer 42 for storing the collected projection image data D4, and a volume data D5. A large number of processors 43,
Data processing between the frame buffer 42 and the processor 43 is controlled and the volume data D5
Is input to an image display device and an image processing device (both not shown). The data acquisition subsystem 41 and the VME control means 44 are connected to a system controller 50 that controls the entire radiation projection image forming apparatus 1, and the data acquisition subsystem 41 is also connected to the X-ray source control means 19. .

The radiation source 10 uses an electron beam L1 emitted from an electron gun (not shown) to
By scanning the entire surface of the collimator 10a, the target collimator 16 irradiated with the electron beam L1 is scanned.
X-rays are generated from a target surface (not shown) (see SPIE VOL. 2708 P140 to P149; especially P142). The target / collimator section 16 is for generating X-rays L2 on the target surface and irradiating the subject 9 with the X-rays L2 in the form of a beam, and has many collimator holes 17. X-ray source control means 19 is connected to the radiation source 10, and the generation and scanning of the electron beam L1 are controlled by the X-ray source control means 19. The X-ray L2 passing through each collimator hole 17 is applied to the radiation detector 2
0 so that each collimator hole 17
And the scanning pitch are set.

The deflection yoke 11 scans the target surface by changing the direction of the electron beam L1. By this scanning, the collimator holes 17 are sequentially switched, and the X-ray beam is emitted from each collimator hole 17 to the subject 9. Is done. That is, each collimator hole 17 corresponds to a minute radiation source that emits the X-ray beam L2.

The radiation source may be any one capable of irradiating a subject with radiation while sequentially switching among a large number of radiation sources arranged on a surface, and is not necessarily limited to the above-described configuration. It is not something to be done.

The radiation detector 20, as shown in FIG.
A total of 96 radiation detection elements 21 (up to 12 in all directions)
Are arranged in a circle. Each detection element 21 detects the X-ray beam L2 transmitted through the subject 9, and inputs the detection signal S to the A / D converter 30 at the subsequent stage. As each detection element 21, any element may be used as long as it can detect X-rays. For example, various types such as a photomultiplier, CZT (Cd, Zn, Te), CdTe, a solid-state radiation detector (see Japanese Patent Application Laid-Open Nos. 1-216290 and 10-215378), a combination of a scintillator and a CCD imaging device, and the like. Can be used. In addition, the point of detecting radiation while sequentially switching the collimator holes 17;
In view of the fact that radiation is detected at each rotational position (radiation projection direction) while rotating the radiation source 10 relatively around the subject 9, it is preferable to use a radiation source that can detect radiation in real time.

In this embodiment, a photomultiplier is used as a radiation detecting element, and a scintillator unit 23 for converting X-rays into visible light is provided at a stage preceding the photomultiplier unit 22, and the converted visible light is transmitted to a fiber 24. To guide the light to each photomultiplier 21 (SPIE VOL.2708 P140 to P14
9; see especially P142). Similarly to the photomultiplier, the scintillator section 23 is formed by arranging a total of 96 scintillator elements 23a in a vertical and horizontal direction, and a total of 96 scintillator elements 23a (FIG. 2C).

Hereinafter, the radiation projection image forming apparatus 1 having the above configuration will be described.
The operation of will be described.

The radiation source 10, which has received a command from the X-ray source control means 19, generates an electron beam L1 and scans the entire target surface of the target collimator 16 with the electron beam L1. By the scanning of the electron beam L1, an X-ray L2 is generated from a portion of the target surface irradiated with the electron beam L1. This X-ray L2 is formed by the collimator of the target collimator unit 16 into a beam-like X-ray L2 directed toward the radiation detector 20,
The subject 9 is irradiated. The X-ray L2 carrying the subject image transmitted through the subject 9 is incident on the radiation detector 20. The radiation detector 20 detects the X-ray L2 and outputs a detection signal S. The detection signal S is converted into image data D1 by the A / D converter 30.

As described above, since the radiation source 10 scans the target surface with the electron beam L1 in response to the command from the X-ray source control means 19, the collimator holes 17 are sequentially switched, and the different positions of the subject 9 are different. X-ray L transmitted through
2 sequentially enter the radiation detector 20. Here, the X-rays L2 emitted from the collimator hole 17 and directed to the full width of the radiation detector 20 can be regarded as a group of micro X-ray beams that irradiate each detection element 21.

The focal plane image forming means 31 converts the X-ray information (image data D1) emitted from each of the collimator holes 17 and transmitted through the subject 9 by using a so-called back projection method.
In synchronization with the scanning signal of the electron beam L1 from the source control means 19, that is, in synchronization with the switching of the collimator hole 17, they are acquired in time series, and the radiation detector 20 is obtained.
By adding and normalizing only the information corresponding to a certain position (pixel point) in each of the plurality of focal planes existing between the and the collimator hole 17 and performing the same for the other pixel points as well, Form a focal plane image at the focal plane.

This mechanism can be represented as shown in FIG. 3 by taking a collimator hole row (source row) and a detection element row as an example. As shown in the figure, it can be seen that a plurality of (four in this example, A to D) focal planes are formed between the source row and the detection element row. The number of focal planes, the number of pixel points on each focal plane, and the like depend on the number and arrangement pitch of the collimator holes 17 and the detection elements 21 and the distance between the source row and the detection element rows.

Since this geometrical relationship depends on the device configuration and can be grasped, when a pixel value for a certain pixel point on a certain focal plane is obtained, the X-rays emitted from any source are used. It is possible to know which detection element information to add to the obtained information. For example, the focal plane B shown in FIG.
The pixel value of the pixel point B1 is information (hereinafter referred to as “17a
→ 21u ”), 17b → 21t, 17
c → 21s, 17d → 21r, 17e → 21q and 1
What is necessary is just to add six information of 7f → 21p. That is,
For the focal plane B, a focal plane image is obtained by adding information from the six beams. Such a correspondence is set in advance, and a focal plane image for each focal plane is formed based on the image data D1 detected by photographing.

Here, considering a certain pixel point on a certain focal plane, since the distance between each collimator hole 17 and the detecting element 21 is different, the X-ray intensity is different according to the line length, and an appropriate focal plane image is obtained. Can not be obtained. Therefore, when obtaining a pixel value for each pixel point, weighting according to the distance is performed and added instead of directly adding information having different line lengths.

The focal plane image thus formed is further subjected to normalization processing. To perform the normalization process,
Since the number of beams constituting the pixel points of each focal plane image is different, it is for correcting the difference.

Next, the projection image forming means 33 forms a projection image based on each focal plane image as follows. The number of pixels (density) of each focal plane image and the pixel position in the direction in which the detection elements 21 are arranged (focal plane direction; X direction in the drawing) are different for each focal plane. Therefore, first, the image conversion processing means 32
Thus, interpolation processing such as magnification correction and pixel density conversion is performed on each focal plane image to adjust the pixel position. afterwards,
The projection image forming means 33 adds in the direction connecting the detection element 21 and the collimator hole 17 (the Y direction in the drawing), that is, adds the pixel values of the same pixel position of each focal plane image, thereby obtaining the subject 9 Form a projection image. As the interpolation processing, any processing may be used as long as a projection image can be formed based on a plurality of focal plane images, such as linear interpolation, higher-order interpolation, and filtering. In addition to this interpolation processing, gradation processing such as density adjustment and contrast adjustment, response adjustment, and the like may be performed. Further, if interpolation processing, gradation processing, and the like are performed not only in the focal plane direction but also in the direction connecting the detection element 21 and the collimator hole 17, a more desirable projected image can be formed.

When the projection image data D4 at the predetermined rotation position (projection direction) of the radiation source 10 and the radiation detector 20 is obtained in this manner, the radiation source 10 and the radiation detector 20 are moved around the subject 9. By rotating the subject 9 by a predetermined angle around the center, the projection image data D4 at the rotated position is obtained in the same manner as described above. Such processing is repeated until the projection image data D4 over the entire circumference of the subject 9 is obtained.

The projection image data D 4 is input to the data collection subsystem 41 of the three-dimensional image forming means 40 and is temporarily stored in the frame buffer 42.

The volume data D5 is obtained by a parallel processing unit having many processors 43. When obtaining this volume data D5, a Feldkamp algorithm (Feldkamp LA, Davis LC, Kress JW,
Practical cone-beam algoritm. J Opt Soc Am A 1984;
1: P612 to P619), and a well-known calculation method for reconstructing three-dimensional data can be used. Here, description of how to obtain the volume data D5 will be omitted.

The obtained volume data D5 is VME
The data is input to the image display device or the image processing device via the control unit 44. The image display device displays a three-dimensional image based on the volume data D5, and a sagittal tomographic image (normally interrupted layer image), a rendering image, and the like obtained by processing the volume data D5 by the image processing device.

As described above, according to the present invention, a plurality of radiation detecting elements detect subject transmission information based on radiation sequentially emitted from a large number of radiation sources arranged on a surface, and the predetermined information within the subject is detected. In a radiographic image forming apparatus that acquires a focal plane image in a focal plane, not only a focal plane image but also a projection image can be easily formed. If a large number of projection images are acquired, volume data can be acquired by the same method as the conventional cone beam CT, and a three-dimensional image or tomographic image can be displayed on a display device. Become.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a radiation image forming apparatus according to the present invention.

FIG. 2 is a view showing details of a radiation detector;
Plan view of photomultiplier section (B), plan view of scintillator section (C)

FIG. 3 is a diagram illustrating a focal plane formed by a radiation source and a radiation detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radiation projection image forming apparatus 9 Subject 10 Radiation source 16 Target collimator part 17 Collimator hole (corresponding to a radiation source) 20 Radiation detector 21 Radiation detection element 30 A / D converter 31 Focal plane image forming means 32 Image conversion processing Means 33 Projected image forming means 40 Three-dimensional image forming means L1 Electron beam L2 X-ray beam

Claims (4)

[Claims] A radiation source for irradiating a subject with radiation while sequentially switching each of the radiation sources; and a radiation source emitted from each of the plurality of radiation sources. Radiation detecting means in which a plurality of detecting elements for detecting transmitted radiation are arranged, and a focal plane image on a plurality of focal planes between the radiation source and the radiation detecting means based on an output signal of the detecting element. A radiation projection image forming apparatus, comprising: a focal plane image forming unit that forms; and a projection image forming unit that forms a projection image of the subject based on the plurality of focal plane images. 2. The method according to claim 1, wherein the focal plane image forming means performs weighting correction according to each line length of the radiation when the detecting element detects the radiation, and adds each output signal of the detecting element. 2. The radiation projection image forming apparatus according to claim 1, wherein the focal plane image is formed. 3. For each of the plurality of focal plane images,
The image processing apparatus further includes image conversion processing means for performing image conversion processing such as magnification correction, pixel density conversion, gradation processing, response adjustment, and the like, wherein the projection image forming means outputs the processed focal plane image to which the image conversion processing has been performed. The radiation projection image forming apparatus according to claim 1, wherein the projection image is formed based on the projection image. 4. A rotation unit for rotating the radiation source and the radiation detection unit around the subject relative to the subject to change a projection direction of radiation on the subject, and a plurality of phases for the subject. The radiation projection image forming apparatus according to any one of claims 1 to 3, further comprising: a three-dimensional image forming unit that forms a three-dimensional image of the subject based on the projection images in different projection directions. apparatus.