JPH01118756A - Scattered x-ray camera - Google Patents

Abstract

PURPOSE:To depict a subject as a high-contrast image by providing shielding bodies which are disposed near an X-ray detector and allow passage of only the scattering rays of specific angles as well as a mechanism which moves the X-ray source, the respective shielding body and the X-ray detector relatively to the subject. CONSTITUTION:The X-rays generated from an X-ray tube 11 are condensed by the shielding bodies 12, 13 to a pencil beam. The pencil beam X-ray is projected on the subject 14 and is partly absorbed in the subject 14 and is, in some cases, partly scattered by the same. The scattered components include the Thomson scattering having coherency and the Compton scattering having no coherency. The Compton scattering does not reflect the structure of materials. The Thomson scattering reflects the structure of materials and possesses the scattering peaks having the scattering angles specific to the respective materials; therefore, the shielding bodies 18, 19 made of lead which allows passage of only the scattering rays of the specific scattering angles to the X-ray detector 16 are disposed. The subject is thus depicted as the high-contrast image.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an X-ray imaging device, and in particular, by detecting scattered X-rays, it is possible to highly identify tissues with a small contrast difference and for which identification was conventionally difficult. The present invention relates to a scattering X-ray imaging device suitable for rendering a contrast image.

[Prior art] The conventional device is described in Radiology Vol. 148, No. 1 (1
983), pp. 259 to 264 (Radioro
gy, vol, 148. Ncl (1983),
X-rays from an X-ray source, as described in
Image information was obtained by irradiating a subject with X-rays and detecting the transmitted X-rays with a two-dimensional or -dimensional sensor. Scattered X-rays from the subject cause blurring on the image, so they are removed using grids and slits.

Images were obtained using only non-scattered components.

[Problem that the invention seeks to solve]

In the above conventional technology, since only the X-rays that pass through the object are detected, the contrast (C) of the obtained image is as follows: (Δμ) and the size of the object (d). Therefore, if either Δμ or d becomes smaller, it becomes difficult to identify the object. The relationship between the contrast that serves as the discrimination limit and the size of the object is shown in a contrast detail diagram (Contrast Detail Diagram).
Diagran+ :CDD)) given by the curve,
When an X-ray film/intensifying screen is used as an X-ray detection system, the result is shown in Figure 4.

(Cohen et al.; Medical Physics Vol. 8.

(No. 3, pp. 358-367) Here, considering an object of 5II 1 m, the discrimination limit is about 1.5% for the contrast difference, and about 0.0% for the absorption coefficient difference.
The limit is 03''/Cal. Table 1 shows the differences in the X-ray absorption coefficients of various materials, and it can be seen from this that it is difficult to distinguish between muscle and fat under the above conditions.

The purpose of the present invention is to provide an X-ray diagnostic device that can detect lesions at an early stage by using scattered X-rays to visualize tissues with high contrast, which were conventionally difficult to identify due to low contrast differences. It's about doing.

Table 1: X-ray absorption coefficients of various substances [Effect] Water, muscle, fat, bone, keys, brain white matter, brain gray matter.

Water, acrylic, polycarbonate, polystyrene.

Differential scattering cross section of coherently scattered X-rays from polyethylene and nylon (Purding et al.; Journal of Optical Society of America, Vol. 4
Volume, No. 5, 933-944゜1987) is shown in Figure 5a.
The coherent scattered X-rays shown as = f reflect the structure of each substance and have a maximum scattering probability at a certain scattering angle. Note that the horizontal axis X in the figure represents the change in the wave number vector of X-rays, which is given by the following equation.

X=-sin(θ/2).

λ However, θ is the scattering angle and the first means the wavelength of the X-ray. From this, it can be seen that in the case of small-angle scattering, X is approximately proportional to the scattering angle. Here, when the scattering angle is adjusted to the peak position of fat, the scattering probability is approximately 2:1 between fat and muscle, and unlike the case of transmitted X-rays, the contrast does not depend on the size of the object, and the contrast is 2:1. You get the difference.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. FIG. 1a shows the overall configuration. X-rays generated from the X-ray tube 11 are turned into a pencil beam by the shields 12 and 13. The shielding body 12.13 has a structure that partially allows X-rays to pass through,
Details will be described later. In addition, the material must completely shield X-rays, so it is typically lead, tungsten,
uranium.

In this embodiment, lead is used in consideration of economic efficiency. Next, the pencil beam X-rays are irradiated onto the subject 14, some of which are absorbed by the subject, and
Some may be scattered.

The remaining components do not interact with the subject and therefore proceed as is.

Here, the scattered components include coherent Thomson scattering and non-coherent Compton scattering. Compton scattering does not reflect the structure of the material, while Thomson scattering reflects the material structure, and each material in the beam traveling direction Since the scattering peak has a specific scattering angle, only the scattered rays at a fixed scattering angle can be
A lead shield 18,19 is placed through which the ray detector 16 passes.

As mentioned above, it is also possible to use heavy metal materials other than lead.6 In addition, in the case of this example, the scattering angle was defined by the shielding plates 18 and 19, but since a pencil beam is used, the X-ray detection It is also possible to define the scattering angle by the vessel opening. Therefore,
The shielding plates 18,19 are not absolutely necessary.

Next, a method for obtaining two-dimensional images will be described. Control device 1
7, the X-ray pencil beam is scanned in the direction perpendicular to the drawing, and the table 15 on which the subject 14 is placed is scanned in the direction of the arrow, thereby obtaining two-dimensional image information as sequential information.

Next, an example of the structure of the X-ray shields 12 and 13 that create the pencil beam will be explained with reference to the drawings. FIG. 1 is a view of the X-ray shield viewed from the direction in which X-rays are incident. 12 is a slit made of two lead plates. Reference numeral 13 designates a part of a circular lead plate through which X-rays pass, and is configured to be rotated in one direction by a control circuit 17. Two X-ray shielding plates 12.
X-rays pass only through the common portion of the 13 slits, resulting in a pencil beam. Further, by rotating the circular shielding plate 13, scanning of the X-ray beam is performed.

In addition, since the slit width defines the spatial resolution of the image,
The narrower it is, the better.However, as the narrower it becomes narrower, the X-ray beam intensity decreases, which increases measurement time and requires a large-capacity X-ray tube, making it impractical.In this example, as a compromise, 0.5-2 m, preferably 1.
It was set to 0m.

Next, an example of the structure of the X-ray detector 16 will be explained using FIG. 1C. The shielding bodies 18 and 19 define the scattering angle of scattered X-rays from the subject. Scattered X-rays are collected by a scintillator 20.22 that converts X-ray intensity information into light intensity. Detect with. Furthermore, non-scattered radiation is similarly detected by the scintillator 21, and a conventional non-scattered radiation image can also be obtained. Scintillator used 20
゜21.22 is generally TQ or Na-activated Na I
.

Alkali halide phosphor such as CsI, BaFC1! :
Rare earth element-activated alkaline earth metal fluorohalide phosphors such as Eu”+, CaWOa, GdzOzS (Pr,
In this example, an inorganic scintillator such as Ce, F), etc. is used.
Use dzOzS(P r, Cs, F).

Fluorescence generated when X-rays enter the scintillators 20, 21, 22 is absorbed by the highly translucent light guides 23, 2.
At 4.25, the light is photoelectrically converted by the photodetectors 26, 27 and 28. Since two systems of scattered X-ray information are obtained, they are added by an adding circuit 28. The information on scattered radiation and non-scattered radiation is then processed by a conventional information collection device and image processing device to create a scattered radiation image,
Obtain a dihedral image of the non-scattered radiation image. The light guides 23, 24, and 25 in this configuration are obtained by thermal processing of optical fibers or light-guiding sheet materials. Here, an acrylic sheet with high light transmission efficiency was used.

Furthermore, the photodetectors 26, 27, 28 include photomultiplier tubes,
Selected from photodiodes, etc. Here, a photomultiplier tube with a large diameter and an amplifying effect is used. Another example of the X-ray detector 16 is shown in FIG. 1d. scintillator 2
The fluorescence from 0, 21, 22 is detected by a long photodetector 29, 30, 31 made of an amorphous photoconductive material and converted into an electrical signal. The outputs of the photodetectors 29 and 31 that provide scattered radiation information are added together in an adding circuit 28 to form a single piece of scattered radiation information.

Next, the overall configuration of another embodiment of the present invention is shown in FIG. The fan beam X-rays interact with the object 14, and some are absorbed and some are scattered. scattered rays,
The unscattered lines each consist of a -dimensional line sensor. It is detected by the X-ray detector 202. Furthermore, slit-shaped shields 18 and 19 may be placed near the X feeder 202 in order to more precisely define the scattering angle. The two-dimensional image is obtained by scanning the subject 14 with fan beam X-rays in the body axis direction. That is, it is obtained by moving the platform 15 on which the subject 14 is placed in a direction perpendicular to the fan beam using the control circuit 17.

Further, in order to reduce the load on the X-ray tube 11, the control circuit 17 generates pulsed X-rays.

x1! An example of the detector 202 will be explained using FIG. 2. Scattered radiation and non-scattered radiation are detected by a one-dimensional array sensor 203.
, 204, 205. The m-th X-ray sensors (203-m, 204-m, 205-m) in the X direction each have position information, and among these, 203-m and 205-m
m detects scattered X-rays and 204-m detects unscattered X-rays.

Since 203-m and 205-m have scattered ray information at the same position, addition circuit 206-m performs addition to obtain scattered ray information Ism at location m. The scattered information (Is) and non-scattered radiation information (Ip) at each sensor position are then processed by a conventional information collection device and image processing device to obtain two images: a scattered radiation image and a non-scattered radiation image. Here, each X-ray sensor is
A scintillator combined with a photodetector, a SitH
A semiconductor detector made of a semiconductor such as gIz+CdTe, GaAs, etc. can be used.

Next, the overall configuration of another embodiment of the present invention is shown in FIG. 3a.

X-rays generated from the Xm tube 11 are converted into a plurality of fan beams by the shield 301. Each fan beam xi interacts with the object 14, with some being absorbed and some being scattered. Scattered radiation and non-scattered radiation can each be measured in real time, and two-dimensional X
It is detected by the line detector 302. A slit-shaped shield 30 is placed near the X-ray detector 302 in order to define the scattering angle by itself.
3 to 314 are placed. A two-dimensional image is obtained by scanning a table 15 on which a subject 14 is placed by a control circuit 17 in a direction perpendicular to the fan beam X-rays. here,
An X-ray image intensifier is used as the two-dimensional X-ray sensor 302 capable of real-time measurement.

The resulting image has scattered radiation information on the left and right sides of non-scattered radiation information, as shown in Figure 3. By adding the scattered components, a combination of scattered radiation information and non-scattered radiation information at a certain scanning position can be obtained. Furthermore, scanning only needs to be performed at least during fan beam X-rays.

Further, in order to reduce the load on the X-ray tube 11, the control circuit 17 generates pulsed X-rays.

In the present invention, an X-ray tube is used as the X-ray source, but other light sources may be used, such as SOR (synchrotron orbital radiation).
(a) It is also possible to use light or radioactive isotopes.

〔Effect of the invention〕

According to the present invention, by detecting scattered X-rays, tissues that have conventionally been difficult to identify due to a small contrast difference can be visualized as a high-contrast image.

Furthermore, since conventional images can also be taken at the same time, it is possible to compensate for the drawback of low S/N of scattered radiation images.

[Brief explanation of the drawing]

Fig. 1a is a schematic side sectional view of one embodiment of the present invention, Fig. 1 is a plan view showing an X-ray shield for producing pencil beam X-rays of this embodiment, and Fig. 1C is a schematic side sectional view of an embodiment of the present invention. FIG. 1d is a perspective view showing the structure of another X-ray detector in this embodiment, and FIG. 2a is a schematic side view of another embodiment of the present invention. 2 is a perspective view showing the structure of the X-ray detector of this embodiment, FIG. 3a is a schematic side sectional view of another embodiment of the present invention, and FIG. An explanatory diagram showing the location of scattered rays, Figure 4a is a tissue model diagram for evaluating the contrast of an object, Figure 4 is a COD curve diagram, and Figure 5a is
f is a diagram showing the differential scattering cross section of each material for coherent X-rays. 11...X-ray tube, 12, 13, 201, 301...
X100 1 Figure (71L) CC) (f) Figure 2 (α) (Shishine 3 Figure (t2.n (b) 4L rod 4 Figure (a,) Possessed 4 fushi)

Claims (1)

[Claims] 1. An X-ray source that generates X-rays, a shield that removes a portion of the X-rays, and coherent scattered X-rays that are generated when the X-rays are transmitted through gaps in the shield and then irradiated to the subject. An X-ray detector that detects each of the transmitted X-rays without interacting with the subject, and/or an X-ray detector that is placed near the X-ray detector and allows only scattered rays at a predetermined angle to pass through. shield,
and the X-ray source, each shield, and the X-ray detector to the subject,
Scattering X characterized by having a mechanism for relative movement
Ray imaging device.