JPH02257084A - Method for collecting image free from gamma-ray scattered beam and gamma camera - Google Patents

Abstract

PURPOSE:To accelerate the speed of processing and to improve the resolution of a diagnostic image by collecting the energy spectrum of (gamma)-rays which is made incident on the respective positions of a gamma camera corresponding to the picture element of a collecting image. CONSTITUTION:A window circuit 5 where a command from a main CPU 9 is inputted collects an image P(x and y) in some window width. Next, it collects the energy spectrum E(x, y, and e) of a corresponding position on the image. On the other hand, when the counted value of the energy spectrum is smaller than a prescribed value, the statistical noise of the counted value is reduced by using a filtering coefficient with the aid of an image memory controller 3. Therefore, the collected image P(x and y) is substituted for an image P'(x and y) where a scattered component which is the cause of impairing the determination characteristic of the image is eliminated. As the result, since the scattered beam can be precisely and easily eliminated, the speed of the processing is accelerated and the resolution of the diagnostic image is improved.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention collects diagnostic images of a living body using a gamma camera that injects gamma rays from a radioactive substance administered to the living body. The present invention relates to a gamma ray scattered ray removal image collection method for removing scattered rays in the living body and scattered rays in the gamma camera by window setting, and a gamma camera.

(Prior Art) Conventionally, in nuclear medicine equipment systems, radioactive substances are administered to the human body, and the movement and accumulation are imaged using a gamma camera for diagnosis. In this system,
γ-rays are scattered within the human body, and scattered rays are generated inside the gamma camera (for example, inside the collimator or Nal entillator z9). This scattered radiation is unnecessary for diagnostic information and must be removed. Therefore, as a method for removing scattered radiation components from an image obtained by using a scintillation camera or the like, there has been a conventional method as described in J. Nucl. Med.

14; [17-72, 1972, J, Nucl, MO
d, 25; 490-494.1984, J, Nu
cl, Med, 29; 195-202.1988.
IEIEli, 1”ran, Nuel, 5cicncc
, N532. 78G-79L 1985. These technical contents are the following two methods.

First, as a first method, a window aO is set at the photoelectric peak P1 in the relationship between the count value and the energy spectrum E as shown in FIG. Then, images within the wind ram O are collected and a window bO is set for the Compton scattered component CO at the same time or as the next sequence. Then, the photoelectric peak image A (x, y) and the scattered radiation image S (x,
y), A (x, y)R-
8 (X, Y'). Note that R is the photoelectric absorption peak P1
Let it be a constant that estimates the proportion of scattered rays included in .

Also, a second scattered ray removal method will be explained. Since the scattered rays have a distribution that depends on the position (x, y), images can be collected more accurately than in the first method of removing the scattered rays.

Therefore, in the relationship of 31 numerical values to the energy spectrum E as shown in FIG. 6, a window having a sufficiently narrow window width ΔE is moved from El to Ep having a peak point by ΔE. And each step E1
An image E (x, y) at ~Ep is collected and used as an image of each energy depending on the position of the gamma camera, and a scattered component is determined for each position.

(Problems to be Solved by the Invention) However, the conventional scattered radiation removal method has the following problems. That is, in the method of &'S 1 described above, scattered radiation is removed using only one value of the estimation constant R. However, if the distribution of scattered radiation differs depending on the position, for example, this differs from the actual physical phenomenon, so there is a problem in that the scattered radiation cannot be removed appropriately for the position, resulting in a lack of accuracy in the image.

On the other hand, in the second scattered radiation removal method, in order to improve the accuracy of scattered radiation removal, ΔE must be reduced and many images must be collected. Therefore, image collection processing takes more time than necessary.

Furthermore, in order to remove the scattered radiation of a nuclide having two or more photoelectric peaks P, more images must be collected, which poses a problem of requiring a long time.

Therefore, an object of the present invention is to provide a γ-ray method that can accurately and easily remove scattered rays of γ-rays within the human body or scattered rays inside a gamma camera, even if these scattered rays depend on the position of the gamma camera.
An object of the present invention is to provide a method for collecting images that eliminates scattering of rays and a gamma camera.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention takes the following measures. That is, the present invention collects a diagnostic image of the living body using a gamma camera that receives gamma rays from a radioactive substance administered to the living body, and from this collected image, the scattered rays within the living body and the scattered rays within the gamma camera are detected using a window. In an image collection method for removing scattered rays of gamma rays by setting, the energy spectrum of the gamma rays incident on each position of the gamma camera at the same time as or during the collection of the diagnostic image corresponds to the pixels of the collected image. The ratio of the scattered rays is determined from the energy spectrum of each position, and the scattered ray components are removed for each pixel of the collected image based on this ratio.

The main body of the gamma camera is equipped with a plurality of scintillators and a plurality of photomultiplier tubes, receives γ-rays from a radioactive substance administered to a living body, and outputs a position signal x+Y and an energy signal Z proportional to the energy of the γ-rays. a first memory that stores the collected image at a position addressed by the position signal X+Y when the energy signal Z input from the gamma camera body is within a predetermined value range; and an energy signal input from the gamma camera body. a second memory for storing Z as an energy spectrum for each position; and a control means for controlling writing of the energy signal Z to the second memory and writing of the collected image to the first memory. It is prepared.

(Effects) By taking such measures, the following effects are achieved. By collecting the energy spectrum E that depends on the position (x, y) at the same time as the image acquisition or subsequently, the entire image of the position-dependent spectrum can be accurately processed, and the ratio of scattered rays can be determined from this spectrum. Multiply the collected image by As a result, scattered rays at each camera position can be accurately and easily removed, resulting in faster processing speed and improved resolution of collected images. For example, when images of two or more types of nuclides that emit gamma rays of two or more energies or nuclides of different energies are collected at the same time to remove scattered rays, this can be done particularly accurately and easily.

(Embodiment) FIG. 1 is a schematic block diagram showing an embodiment of a gamma camera to which the γ-ray scattered ray removal image acquisition method according to the present invention is applied. In the same figure, the scintillation camera body 1
A gamma camera (also called a gamma camera) is equipped with a scintillator and multiple photomultiplier tubes. The A/D converter 2 receives the position signal X+Y from the scintillation camera body 1.
and converts the energy signal Z into a digital signal. The window circuit 5 issues a write command S to the image memory controller 3 when the energy signal E input from the A/D converter 2 falls within the width between the upper limit WU and the lower limit WL of a predetermined window set by the main CPU 9.
It outputs 1. The xy address selector 6 selects x based on the position signals x and y input from the A/D converter 2.
y address is selected. When the image memory controller 3 as a control means receives the write command S1 from the window circuit 5, the image memory controller 3 changes the content of the memory address corresponding to xy on the image data memory 4 to 1 based on the address signal from the xy address selector 6. This is to record image data by adding them. Also, the energy signal Z input to the window circuit 5 is sent to the xy address selector 6.
is identified by the position (X, Y). Further, the wave height separator 7 identifies the wave height value of Z, and the content of the memory corresponding to the channel corresponding to the size of Z of the spectrum corresponding to the position (x, y) of the spectrum data memory 8 is divided into 1.
The energy spectrum (XY, e) corresponding to the position is collected simultaneously with the image collection. In other words, the data memory 8 stores the position of the scintillation camera (X, Y
) is stored as an energy spectrum Z or a combination of energy spectra (X, Y, e). Further, the window circuit 5 sets a window width of about 20 to 30% of the photoelectric peak energy based on a control signal from the main CPU 9. The image memory 4 as the first memory stores the γ-ray segment right image P (x, y) of the gamma camera coordinates (x, y) of the energy input to the window width set by the window circuit 5. be. A spectral data memory 8 serving as a second memory stores the energy spectrum for each position (x, y) on the field of view of the gamma camera, and stores the energy spectrum of the γ-ray in the photoelectric peak stored in the image memory 4. Among them, the spectrum E (x, y, e) collected with a sufficiently wide window width to estimate the scattered component ratio is stored.

FIG. 3(a) shows the collected γ-ray distribution image (hereinafter referred to as collected image or P (x, y)).

Moreover, each pixel position (i-1, j; i.

j; i+t, j) (hereinafter referred to as energy spectrum or E (x
, y, e). ).

Next, a gamma ray scattering removed image acquisition method and a gamma camera will be described with reference to FIGS. 1 and 4.

First, the diagnostic image including γ-ray scattered rays from the gamma camera 1, i.e., the position signals x, y and the energy signal Z, are
The D converter 2 converts the signal into a digital signal. The position signals x and y are input to the image memory controller 3 and the xy address selector 6, and the energy signal Z is input to the window circuit 5 and the pulse height separator 7. The window circuit 5 receives instructions from the main CPU 9.
collects an image P (x,y) with a certain window width, e.g. 20-30% width with respect to the photoelectric peak energy. At the same time, with the window width fully opened by the window circuit 5, an energy spectrum E (x, y, e) corresponding to the position on the image is collected (step A
). Next, it is determined whether the counted value of the collected energy spectrum is large or not (step B). If the counted value is large, the photoelectric peak position ] is detected for E (x, y, e) (step C). Window position (upper limit position WU) set when collecting P (x, y) roughly
, the area of the photoelectric peak within WL≦e≦WU with respect to the adjustment position WL) (Net PeakA rea)
seek.

NPA (x, y) B (x, y) = (E (x, y, WU) + E (x, y, wl) IX (W
U-WL)/2 or photoelectric peak area NPA (x, y
) and the scattered radiation component B (x, y) are determined (step D).

Then, the diagnostic image P (x, y) is multiplied by the ratio of scattered rays. i.e. p(x,y)xNpA(x,y)/fNPA(x,y)
Scattered rays are removed by +B(x,y)1 to obtain a scattered ray removed image P' (step E).

On the other hand, in step B, if the count value of the energy spectrum is smaller than the predetermined value, the image memory controller 3 sets the filtering coefficient a1 al =all-=-a21+L L
Filter processing is performed using the following formula to reduce the historical noise in the count values.

E' (i, j, k) Then, after blurring the position information to obtain a more accurate energy spectrum (step F), the processing from step C onwards is performed.

Therefore, the collected image P (x, y) is an image P' (X
, y). As described above, according to this embodiment,
Energy spectrum E depending on position (x,,y)
At the same time as image collection, the entire position-dependent spectrum image is accurately processed, the ratio of scattered rays is determined from this spectrum, and the collected image P (x, y) is multiplied by this ratio.

As a result, scattered radiation can be removed accurately and easily.
Processing speed becomes faster and resolution of diagnostic images improves. Further, for example, when images of two or more types of nuclides emitting gamma rays of two or more energies or nuclides of different energies are collected simultaneously and scattered rays are removed, this can be done particularly accurately and easily.

In addition, the scattered radiation removal steps C-E of the acquired image shown in FIG.
In the process of , the scattered component of the energy spectrum is the energy spectrum E (i
Scattered radiation was removed by assuming that the shaded portion B1 of -L, j, Ic) was only the base background of the energy spectrum.

However, in clinical tests, R
Since the gamma rays emitted from 1 (radioisotope) are scattered even inside the living body, the shape of the photoelectric peak is compared to the case where there is no scatterer in the living body, and if this is S (x, y), A more accurate NPA is NPA' (X, y) = NPA (x, y) - 3(x
, y).

This processing method will be specifically explained with reference to FIG.

E (x, y, e) is the energy spectrum in clinical practice, the energy spectrum in the air without scatterers, and the response function of the scintillation camera is Ein
If air (x, y, e), then S (x
, y) However, E]nair is multiplied by a real number so that, for example, the peak and the shoulder of the curve match most in p c<e<W U, and At (real number) such that becomes mjn is obtained.

Next, a second embodiment of the present invention will be described. The gamma camera is used to perform tomographic images, single photon emission CT (hereinafter referred to as 5
A case in which the method is applied to PECT (referred to as PECT) will be explained.

First, let P (x, y) be an image collected by the scintillation camera described above. The gamma camera rotates 360° or 180° around the subject and collects projection images every n degrees to obtain a projection image P (x, y, θ). For example, n
= G°, the energy spectrum is collected for each projection image, and E (x.

V+ e+ θ) is obtained. Here θ represents the collected angle. As a result, scattered radiation removal for each angle θ is performed using the fourth method described above for the projected image P (x, y, θ) for each angle θ.
Perform the process according to the steps shown in the figure. Even in an apparatus using such a tomographic image, the same effects as described above can be obtained.

In addition, if the energy spectrum count value is insufficient and therefore sufficient accuracy cannot be obtained, the distribution of scattered rays can be primed by assuming that there is no angular dependence in the projected image.・The energy vector I・ram for each n angle may be used as an average value.

Next, a '3rd embodiment will be explained with reference to FIG. Note that the same parts as in FIG. 1 are designated by the same number 71, and the details thereof are omitted. The split circuit 15 divides the A/D converted position signal into a specific range; XO<X<XI, yO<
Only the position signal Xy where Y<yl is output to the next window circuit 5. Therefore, the position signals x, y in a specific range are
Under certain conditions, the image memory controller 3 stores image data in the corresponding X2 and Y addresses of the image data memory 4, and under other conditions, the image data is stored in the (x, y) range set by the split circuit 15 (hereinafter referred to as split). Energy spectrum E (x, y, e
) are collected by the main CPU 7.

In this apparatus, acquisition of scintigram images and energy spectra will be explained with reference to the flow diagram shown in FIG. First, 0<x y<X maX, Y
Let it be l1laX. Split circuit 15 by CPU7
is fully opened in the range of 0<x<xmax, O<y<yllaX (step a). and window circuit 5
Step b), the CPU 7 sets a necessary window width, for example, 20% of the width of the main peak, and collects an image P (x, y) (step C). and m
, n are initialized (step d), and the window circuit 15 is set fully open by the main CPU/memory 17 (step e). Furthermore, m6ΔX≦X< (m+1) ・
The split circuit 15 is set for Δx, m” Δy≦y<(m+1)・Δy (step f).Then, the energy spectrum E (X
Collect and store I y,e) (step g). The next m and n are set by the main CPU 1.7 (step h). When the next m and n are set here, in the already collected image P (x, y), m and n are set within the range of only the positions exceeding a certain count value (step 10
゜If the next m and n are not set, the sequence ends (step J).

Therefore, even if the energy spectrum E (xy, e) and the collected image P (x, y) cannot be collected at the same time, except for early dynamic tests, the information finally obtained is Scattered radiation can be removed in the same way as those collected at the same time.

In actual clinical practice or 5PECT acquisition, energy spectrum E (x,
The time can also be shortened by making θ larger than the collection angle n in y, e).

However, collecting the energy spectrum of the entire image range would take a very long time. Therefore, in the image P (x, y, θ) collected prior to collecting the energy spectrum, a region of interest (hereinafter referred to as ROI) is set for the positions where the count value is above a certain level, and the energy spectrum is collected only within the ROI. The write command s1 may be used to perform the following operations.

Note that the present invention is not limited to the embodiments described above, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] According to the present invention, by collecting the energy spectrum E that depends on the position (x, y) at the same time as image acquisition or subsequently, it is possible to accurately process one entire spectrum image that depends on the position. By determining the ratio of scattered rays from this spectrum and multiplying the collected image by this ratio, the scattered rays can be accurately and easily removed, increasing processing speed and improving the resolution of diagnostic images. For example, when images of nuclides that emit gamma rays with two or more energies or two or more nuclides with different energies are collected at the same time to remove scattered rays, gamma rays can be easily and accurately removed. A scatter-free image acquisition method and a gamma camera can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of a gamma camera device to which the gamma ray scattering removal image acquisition method according to the present invention is applied, FIG. 2 is a schematic block diagram showing a third embodiment of the present invention, and FIG. FIG. 4 is a flowchart showing the scattered radiation removal image acquisition method in the embodiment shown in FIG. 1, and FIG. A schematic diagram showing the relationship with the count value, FIG. 6 is a flow diagram showing the scattered radiation removal image acquisition method in the embodiment shown in FIG. FIG. 2 is a schematic diagram illustrating an image collection method. 1... Gamma camera, 2... A/D converter, 3...
- Image memory controller, 4... Image data memory, 5... Window circuit, 6... xy address selector, 7... Wave height separator, 8... Spectrum data memory, 9...・Main CPU, 15...Split!・Circuit, P (x, y)...Collected image, E (x
, y, e)...Energy spectrum, Pl...
Photoelectric peak. Applicant's agent Patent attorney Takehiko Suzue

Claims (2)

[Claims] (1) A diagnostic image of the living body is collected by a gamma camera that receives gamma rays from a radioactive substance administered to the living body, and from this collected image, scattered rays within the living body and scattered rays within the gamma camera are detected by window settings. In the image acquisition method for removing scattered rays of gamma rays, the energy spectrum of the gamma rays incident on each position of the gamma camera is determined at the same time as or during the acquisition of the diagnostic image, corresponding to the pixels of the acquired image. Scattered ray removal of gamma rays, characterized in that the ratio of the scattered rays is determined from the energy spectrum of each position, and the scattered ray component is removed for each pixel of the collected image based on this ratio. Image collection method. (2) A plurality of scintillators and a plurality of photomultiplier tubes are arranged to input γ-rays from a radioactive substance administered to a living body and output position signals x, y and an energy signal Z proportional to the energy of the γ-rays. a first memory that stores a collected image at a position addressed by the position signals x and y when an energy signal Z input from the gamma camera body is within a predetermined value range; A second memory that stores the energy signal Z input from the main body as an energy spectrum for each position, and writes the energy signal Z to the second memory and the collected image to the first memory. A gamma camera characterized by comprising a control means for controlling the camera.