JPS5975139A - Method and device for forming x-ray tomographic image - Google Patents

Abstract

PURPOSE:To obtain data with less variance in detection sensitivity with simple constitution by recording data on projection and data on the output of an X-ray source in an X-ray detection material which moves in synchronization with the rotation of an X-ray source and forming a tomographic image in accordance with the recorded data. CONSTITUTION:An X-ray source S irradiates a fan beam-like X-ray toward object OBJ and the periphery thereof, and the data on the projection and the data on the output of the X-ray source are recorded in an X-ray detection material SP which rotates in synchronization with the source S. The material SP moves in an arrow direction at every rotation by a slight angle of the source S and records the data for each of the angles in a bar graph. The recorded data is conducted to an image reproducer (not shown), by which a tomographic image is formed. The data on the projection and the data on the output of the X-ray source are simultaneously recorded and therefore the correction of a fluctuation in the output of the X-ray source is made possible without requiring any detector for reference.

Description

[Detailed Description of the Invention] The present invention irradiates a subject with X-rays, detects the amount of X-rays that have passed through the subject, calculates the X-ray absorption coefficient of each part of the tomographic plane of the subject, and based on this, The present invention relates to an X-ray tomographic image creation method and apparatus for reconstructing a tomographic image of the subject.

Conventionally, X-rays are projected onto a subject, and the X-rays transmitted through the subject are
Detect the intensity of the rays, obtain projection data, use the combination coater to calculate the X-ray absorption coefficient of each part of the tomographic plane of the object from this projection data, and reconstruct the tomographic image of the object based on this. Configuring X-ray CT (COml)Llted Tomogr
aphy) is known.

In such X-ray CT, there are various methods for obtaining projection data. The one shown in FIG. 1 is of the fan beam type, which is currently widely used.

In this method, X-rays are emitted from an X-ray source S in the form of a fan beam, and a large number of XI! beams, such as 256 or 512 fan beams, pass through the object OBJ. X-ray source S and detector array DFT are used to detect the object OB.
It is configured so that it can rotate as a unit around J,
These are rotated in small angular increments to obtain projection data at each angular position.

By the way, the above-mentioned detector array DET has a configuration in which several hundred detectors are arranged at narrow intervals in order to increase the resolution of the cross section (&ξ) by 1, but in order to obtain good image quality,
Since the sensitivity of each detector array is required to have little variation and each detector is required to have high sensitivity, it is extremely expensive.

In addition, the use of a detector composed of an ionization chamber or the like will result in large errors, and if this is rotated integrally with the X-ray source, the
However, there was a drawback that the amount itself was large -b.

In addition, since the output (dose) of the X-ray source S may fluctuate during irradiation, the X-ray source S
7) Reference detector R that detects the output of the X-ray source S nearby
D was rearranged and the projection data was corrected using the output of the reference detector RD. However, this configuration complicates the device.

The present invention aims to eliminate these drawbacks, and its purpose is to obtain a large number of projection data with little variation in detection sensitivity despite its simple structure, and to create high-resolution and accurate tomographic images based on this data. An object of the present invention is to provide a method and apparatus for creating an X-ray tomographic image.

The method of the present invention to achieve this objective rotates an X-ray source and an X-ray detection material integrally around a subject, and moves the X-ray detection material in synchronization with the rotation of the X-ray source. Accordingly, the projection data and the X-ray source output data are recorded on the X-ray detection material, and a tomographic image is created based on the recorded data and the X-ray source output data.

Furthermore, the device of the present invention can be used to direct xI! toward the subject and its surroundings.
an X-ray source that irradiates i1; and an X-ray source that rotates integrally with the X-ray source around the subject and moves in synchronization with the rotation;
An X-ray detection material that receives X-rays that have passed through the subject and its surroundings and records them as projection data and X-ray source output data, and reads out the projection data and X-ray source output data recorded on the X-ray detection material. It is equipped with a readout device and an image reconstruction device that reconstructs a tomographic image based on the projection data output from the readout device and with correction using the X-ray source output data! It is characterized by these points.

Hereinafter, the method and apparatus of the present invention will be explained in detail using the drawings.

FIG. 3 is a configuration diagram showing an embodiment of the projection data recording section used in the present invention, in which (a) is a plan view of the X-ray source S on the plane of rotation, and (b) is a plan view of the projection data recording section (a). It is a side view seen from a direction perpendicular to the rotation surface. In both figures, SP is an X-ray detection material that replaces the conventional detector array, and is configured so that it can rotate around the object OB J integrally with the X-ray source S, as in the conventional case. The X-ray source S of this embodiment irradiates a fan beam-shaped X-ray toward the subject and its surroundings, and the X-ray detection material SP is as shown in FIG. Each time the X-ray source S rotates by Δθ and irradiates fan beam-shaped X-rays, the X-ray source S rotates in a direction perpendicular to the beam plane, as shown by the arrow in Fig. 3 ([1)]. It is configured to move by Δ×.

This X-ray detection material SP, which will be described in detail later, is manufactured using, for example, a photostimulable phosphor (usually, a photostimulable phosphor powder is mixed with a suitable binder, applied to a base, and finished into a plate shape). It is irradiated with X-rays while moving as described above, and as shown in FIG. 4, data of each pico for each Δθ can be recorded in a striped pattern at intervals of ΔX.

Here, the data recorded on the X-ray detection material SP is
Projection data D1 written in the central part by the irradiation of the X-rays that passed through J, and projection data D1 written outside of the projection data D1 by the irradiation of the X-rays that passed around the area A without passing through the object OBJ. X-ray source output data D2 (see FIG. 4). This X-ray source output data D2 is data used to detect the output of the X-ray source S and correct fluctuations in the projection data D1 due to the fluctuations thereof.

Note that Δθ is usually about 1°, and Δ× is 1 to 3 mm.
However, the movement of the X-ray source S and the X-ray detection material SP does not necessarily have to be intermittent and may be continuous.

In the X-ray detection material SP made of a photostimulable phosphor (hereinafter simply referred to as phosphor SP), an afterimage is formed by the X-rays that have passed through the subject OBJ. The projection data D1 and the X-ray source output Y-data D2 can be obtained by irradiating excitation light and detecting the light generated by stimulated luminescence.

FIG. 5 shows an example of a reading device for reading out the IC projection data D1 and the X-ray source output data D2 recorded on the phosphor SP.

In the figure, reference numeral 1 indicates an excitation light 1- which is disposed between an optical deflector (not shown) and a phosphor SP and is deflected by the optical deflector.
The dichroic mirror 2 receiving the incident light is a cylindrical lens serving as a first unidirectional condensing element through which the light transmitted through the dichroic mirror 1 flows. This cylindrical lens 2
is arranged near the phosphor SP and focuses the Okawa excitation light 1- near the surface (including the surface) of the phosphor SP. For example, the spot shape on the surface of the phosphor SP is The optical system is configured to be an ellipse, and the width in the main scanning direction is, for example, 0.1 to 2 mmPij degree, and the width in the sub-scanning direction is the thickness of the fan beam (ie, 15 slices) or slightly smaller than the slice thickness. configured (e.g. 0.3-5mm
(adjusted to the degree). 3 is a photomultiplier tube with a phosphor SP
The light generated by stimulated luminescence is passed through the cylindrical lens 2. The light is received through a dichroic mirror 1 and a filter 4.

In this reading device, main scanning is performed by moving the excitation light in a direction perpendicular to the paper plane of FIG. 5, and sub-scanning is performed by moving the phosphor SP upward in FIG. As a result, the entire surface of the phosphor SP is irradiated with excitation light, and the light generated by stimulated luminescence at each scanning spot is converged in one direction by the cylindrical lens 2, and then by the dichroic mirror 1. It is separated from the excitation light and enters the photomultiplier tube 3 through the filter 4.

As a result, the projection data recorded on the phosphor SP is output from the photomultiplier tube 3 as an electric signal.

The filter 4 is configured to detect the presence of excitation light that is reflected from the back surface of the phosphor SP, transmitted through the cylindrical lens 2, reflected by the dichroic mirror 1, and directed toward the photomultiplier tube 3 (reflected excitation on the phosphor SP). Most of the light passes through the dichroic mirror 1, so the presence of the dichroic mirror 1 is very small. , the transmittance is 1, and the wavelength of the excitation light is A, the characteristic curve F of the filter 4 and the characteristic curve of the dichroic mirror 1 are as shown in FIG. 6, for example. The wavelengths of the main portions of the spectra of the light emitted from the emitted light need to be sufficiently far apart from each other in order to separate the light from the stimulated emitted light.

When using the output beam of a l-18-N (!gas laser) as the excitation light, examples of phosphors that stimulate light at a wavelength that can be easily separated from the excitation light include, for example, Japanese Unexamined Patent Publication No. 4
BaS described in No. 8-804.87.

4: AX (However, A is at least one of DV, Tb, and King m, and X is 0.001≦×<1 mol%)
A phosphor represented by
7) M(+804 :AX <However, △ha HO and D
is at least one type of V, and × is 0.001≦×
≦1 mol %), JP-A-48-
5r804 described in No. 80489: △× (However, Δ is Tm
, Tb and l)y+7),
A phosphor represented by X is 0.001≦×<1 mol%, Na 2804 described in JP-A No. 51-29889
, Ca SQ4.3r 804 and 3a S04, etc., added with at least one of Mn, Dy and Tb, Be O, L described in JP-A No. 52-30487
iF.

M(!2 Fluorophores such as SO4 and Ca F2, JP-A-53
Li2B407 described in No.-39277: CU and Li? B40? :Cu, △q, etc., SrS:Ce, 5111 described in US Pat. No. 3,859,527,
SrS: Ell, Sm, La2O2S: Eu.

Phosphor represented by Sn+ and (Zn, Cd)S:Mn, X (where X is halogen), JP-A-55-1214
7nS described in No. 2: Cu, Pb phosphor, general formula is 3aQ
-x△1zo3: Barium aluminate phosphor represented by Eu (however, 0°8≦×≦10) and whose general formula is M″
Q-x si 02 :A(IEIL/M” +aM
g, Ca, Sr,, 7n, Cd or LtBa, A is Cc, Tb, Fu, Tm, P
b.

At least one of TQ, Bi and Mn, ×
An alkaline earth metal salt phosphor represented by )
FX:aEu” (where X is at least one of [3r and CQ, and X, y and a are each 0<x+y≦
0.6, ×■≠0 and 10"≦a≦5 The general formula described in No. 14 is 1nOX:x△ (where Ln is 1-a, Y
, G (at least one of I and Lu, X is CQ and/or Br, Δ is Ce and/or King, × is Q<x
<0.1), the general formula described in JP-A-55-1214F1 is (BaI
-xMX”)FX:yΔ(However, Mll is Ma, Ca
, Sr.

7n and CQ, X is CG, S
At least one of r and r, A is Eu, Tb,
At least one of Ce, Tm, DV, Pr, 1-1c, Nd, Yb and I3, x and y are O≦×≦
0.6 and O≦y≦0,2). All of these have emission spectra with shorter wavelengths than He-Ne gas laser light. Therefore, by using a color filter as the filter 4, the photomultiplier tube 3
It is possible to block excitation light from entering.

In addition, in terms of light energy efficiency, it is advantageous to use a guichroic mirror 2 that has opposite transmission characteristics for the excitation light and excitation light, and that has a sharp change in characteristics depending on the wavelength. preferable.

Such characteristics can be easily obtained by dielectric multilayer coating.

The projection data D1 and the X-ray source output data D2 read out from the phosphor SP in this manner are led to, for example, an image reproducing device shown in FIG. In FIG. 7, reference numeral 11 denotes an analog-to-digital converter that converts the projection data D1 read out by the photomultiplier tube 3 and the X-ray source output data D2 into digital signals, and its output is converted into the central processing unit of the microcoater (hereinafter referred to as , CPU) 12 or directly by a direct memory access (DMA) method, to a data memory 13 and stored in a projection data storage area and an X-ray source output data storage area in the memory 13. . A program memory 14 stores a reconstruction program using, for example, a Fourier transform method, a successive approximation method, a single convolution method, or a pack projection method for reconstructing a tomographic image. The CPU 12 receives a program start signal and various information from an input device (not shown), executes this program, and calculates the object OBJ using projection data D1 and X-ray source output data o2 stored in the memory 13. Reconstruct the tomographic image. The reconstructed image data obtained in this way is stored in the image data storage area of the memory 13, and read out as necessary.
It can be displayed on the display device 15.

It should be noted that the processes from projection data detection to tomographic image reconstruction do not necessarily need to be processed within the same device; instead, the detection plate SP on which the projection data is recorded may be transferred to a separate device and the reconstruction processing performed there. You can also do this.

, projection data D1 and X-ray source output data D? Although a rectangular plate-shaped X-ray detection material SP is shown as the recording medium, it may be of any shape such as a drum-shape. However, in this case, the drive mechanism of the X-ray detection material,
It may be necessary to partially change the hardware and software, such as position correction of the projection data D1 and the X-ray source output data D2.

Furthermore, the X-ray detection material SP need not be limited to a photostimulable phosphor; any recording medium from which the information can be read out by some means after recording may be used.

Also, X-ray source output data D? It is also possible to configure the recording medium so that it is written only on one side of the recording medium.

According to the method and apparatus of the present invention described in Section 1 below, the following effects can be achieved.

(1) Since a plurality of detection elements with variations are not used, the detection sensitivity is almost uniform over one pico.

Therefore, a tomographic image with good image quality can be obtained.

(2) Compared to the past, a reference detector is not required.

This simplifies the configuration of the device.

(3) It is also possible to configure the detector portion with a single plate, and from this point of view as well, the device can be made smaller and lighter.

(4) The image transport system for transmitting projection data, etc., does not require any wiring such as a signal line for extracting a signal from the detector and a power source, resulting in an extremely simple configuration.

(5) In the conventional method, everything from detection of projection data etc. to tomographic image reconstruction was performed at the same place, but according to the method and apparatus of the present invention, the X cotton plug 110A with recorded projection data etc. It is possible to move to a location and perform tomographic image reconstruction there.

(6) Since projection data is continuously recorded in the feeding direction of the X-ray detection material, it is essentially equivalent to arranging conventional detectors in an IMi space in a minute gap, and can produce high-resolution tomographic images. Furthermore, although high resolution can be obtained, the price is not as high as that of the conventional method.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of fan beam CT, Fig. 2 is an explanatory diagram showing the arrangement of reference detectors in conventional X-ray CT, and Fig. 3 is an illustration of the projection data recording unit used in the present invention. 4 is an explanatory diagram showing the projection data recording state of the X-ray detection material; FIG. 5 is an explanatory diagram showing an embodiment of the reading device which is a part of the device of the present invention; FIG. 6 is an explanatory diagram showing transmittance characteristics of a dichroic mirror and a filter, and FIG. 7 is an explanatory diagram showing an embodiment of an image reproducing device which is a part of the apparatus of the present invention. S...X-ray tm OBJ...Object SP
...X-ray detection material 3...Photomultiplier tube 11...
・AD converter 12...CPU 13.64...Memory 15...Display device Patent applicant Roku Konishi Photo Industry Co., Ltd. Representative Patent attorney Ijima
Osamu Fuji-17... Leather Figure 1 Figure 4 Figure 5 Figure M6

Claims (5)

[Claims] (1) The X-ray source and the X-ray detection material are rotated integrally around the subject, and the X-cotton plug 1 is rotated in synchronization with the rotation of the X-ray source.
The projection data and the X-ray source output data are recorded on the X-ray detection material by moving the A method for creating an X-ray IfJi layer image. (2) The X-ray detection material is a photostimulable fluorophore, and
The method for creating an X-ray tomographic image according to claim 1, characterized in that the projection data is written in the center of the radiation detection material, and the X-ray source output data is written in at least one side of the projection data. . (3) An X-ray source that irradiates X-rays toward the subject and its surroundings; an X-ray source that rotates integrally with the X-ray source around the subject and moves in synchronization with the rotation; An X-ray detection material that receives X-rays passing through the surrounding area and records them as projection data and X-ray source output data, and reads out the projection data and X-ray source output data recorded on the X-ray detection material. X II characterized in that it is equipped with a reading device and an image reproducing device that reconstructs a tomographic image based on the projection data output from the reading device while performing correction using the d X-ray source output data. Tomographic imaging device. (4) The X-ray tomographic image creation apparatus according to claim 3, wherein the X-ray detection material is a photostimulable phosphor. (5) The X-ray source illuminates X-rays in the form of a fan beam, and the X-ray detection material, which rotates integrally with the X-ray source, is configured to move in a direction perpendicular to the fan beam plane. An X-ray tomographic image creation apparatus according to claim 3 or 4, characterized in that: