JPH0996675A - Nuclear medical diagnosis system and separation method for radioactive isotope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate the radioactive isotope(RI) accurately without increasing the volume of data to be processed by employing a plurality of energy windows for separating the components. SOLUTION: A gamma camera body 1 measures the energy and incident position of gamma-rays emitted from RI projected to a specimen and produces an energy signal (z) and position signals (x), (y) which are then digitized through an A/D converter 2. The converted position signals (x), (y) are fed to an image controller 3 and the converted energy signal (z) is fed to a window circuit 7. A CPU 9 functions as the control kernel of entire system and controls the operation of the window circuit 7 and a correction coefficient generating circuit 8 thus measuring the radiation from two kinds of RI projected to the specimen. Components of each RI are then separated based on the measurement data using a plurality of energy windows and two-dimensional images representative of the gamma-ray distribution for first and second RI are presented on a display 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear medicine diagnostic device, and more particularly to a technique for separating two types of radioisotopes when the two types of radioisotopes are used at the same time.

[0002]

2. Description of the Related Art In diagnosis in nuclear medicine, a radioisotope (hereinafter referred to as RI) is selected and administered according to the purpose of diagnosis. Up to now, one type of RI was often administered in one measurement, but two types of R are used because of the advantages such as shortening the diagnostic time and eliminating the positional shift between diagnostic data.
The number of simultaneous administrations of I is increasing. in this case,
The measurement data of the radiation emitted from two types of RI is RI
Need to be separated for each type. However, in nuclear medicine diagnosis, Tc-99m is generally used for blood flow diagnosis and I-123 is often used for nerve / metabolic diagnosis.
The photopeaks of 9m and I-123 are close to each other, and the energy spectrum obtained is the overlap of the energy spectra of two types of RI. In the conventional nuclear medicine diagnostic apparatus, there are two means described below as means for separating each type of RI.

The first is a means for separating the energy spectrums of two types of RI from the portions where there is little influence of the close overlapping (reference "MDDevous Sr, JLLowe,").
JKPayne. “Dual-isotope SPECT imaging with Tc-99
m and I-123: validation by phantom studies. ”J.Nuc
l.Med., vol.33 pp.2030-2035, 1992 '' and `` MD Dev
ous Sr, JKPayne, JLLowe. “Dual-isotope SPECT
imaging with Tc-99m and I-123: clinical validation
using Xe-133 SPECT. ”J.Nucl.Med., vol.33 pp.1919-1
924, 1992 "). Fig. 1 shows an example of the energy spectrum obtained when two types of RI are administered to a subject.
2. This means will be described with reference to FIG. Here, RI having a lower photopeak energy is RI1, and RI having a higher photopeak energy is RI2. The energy spectrum is divided into an energy region 13 lower than the photopeak P1 of RI1, an energy region 14 between the photopeak 1 of RI1 and the photopeak P2 of RI2, and an energy region 15 higher than the photopeak P2 of RI2. Since the two types of RI data most overlap each other in the region 14, the data of this region is not used, and the two types of RI data are calculated using the data of the regions 13 and 15 which are less affected by the overlap. That is, this means utilizes the fact that the energy spectrum of one type of RI ideally becomes a normal curve, the data of RI1 is calculated by doubling the data of region 3, and the data of RI2 is calculated. Is calculated by doubling the data in area 5.

The second is a means for collecting the energy spectrum of each pixel of the nuclear medicine diagnostic image and separating two types of RI from the shape of the obtained energy spectrum (Japanese Patent Laid-Open No. 6-138237). With this means, the shape of the energy spectrum for each pixel is known, and by utilizing this, it is possible to perform accurate separation including correction of the scattered radiation component.

[0005]

In the actually collected radiation, scattered radiation is present in about 30% to 40% of the whole due to the Compton effect in the object and the collimator. The curve part gently drawn on the low energy side of the energy spectrum is this scattered ray component. The first means has a problem that the two types of RI cannot be accurately separated because the influence of the scattered ray component is ignored. RI1 calculated using data on the low energy side
Has many errors.

In addition, the energy spectrum is generally the one for the entire acquired nuclear medicine diagnostic image. On the other hand, since the second means is to obtain the energy spectrum for each pixel, there is a problem that the amount of data to be handled becomes huge and the collection system becomes complicated.

It is an object of the present invention to provide a nuclear medicine diagnostic apparatus and a radioisotope separation method which can solve the above problems and can accurately separate two types of RI without increasing the amount of data to be handled. is there.

[0008]

In order to achieve the above object, the present invention according to claim 1 and claim 7 measures the radiation emitted from two types of radioisotopes administered to a subject, and measures this. Separate multiple radioisotope components by using multiple energy windows on the data.

According to the present invention, in a nuclear medicine diagnosis performed by simultaneously administering two types of RI to a subject, it is possible to accurately separate the two types of RI without increasing the amount of data to be handled.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of means for separating collected data into data for each of two types of RI when two types of RI are simultaneously administered to a subject will be described with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of a nuclear medicine diagnostic apparatus to which the present invention is applied. This nuclear medicine diagnostic apparatus is for setting four energy windows, and includes a gamma camera body 1, an A / D converter 2, an image memory controller 3, and first to fourth image memories 4A as shown in the figure. 4D, first to fourth image processors 5A to 5D, a scattered component removing circuit 6, a window circuit 7, a correction coefficient generating circuit 8 and a CPU 9.

The CPU 9 functions as a control center of the entire system, and controls the window circuit 7 and the correction coefficient generating circuit 8 to remove the gamma ray scattering component from the two-dimensional image by two kinds of RI. The removal circuit 6 causes the two types of RI data to be separated,
2D image showing the gamma ray distribution by RI of the second R
Two-dimensional images showing the gamma ray distribution by I are displayed on the display 10, respectively.

The gamma camera body 1 measures the energy and the incident position of the gamma ray emitted from the RI administered to the subject, and when the energy signal z and the position signals x and y are obtained, these signals are A / It is digitized by the D converter 2. The position signal x output from the A / D converter 2,
y joins the image memory controller 3, while the energy signal z joins the window circuit 7. The window circuit 7 is composed of a window level generating circuit 7A and a window setting circuit 7B. Under the control of the CPU 9, the window setting circuit 7B has windows W1, W2, W3 and W4.
Each time the operation of setting any of the above is performed, the window level generation circuit 7A determines the energy region width for each of the windows W1 to W4 in accordance with the energy signal output from the A / D converter 2, and which image A signal Sn indicating whether to write the image data of each window W1 to W4 in the memory is sent to the image memory controller 3. The image memory controller 3 outputs the image data in the windows W1 to W4 corresponding to the signals Sn received from the window level generating circuit 7A to the first to fourth image memories 4A to 4D, respectively. Write at the address determined by. Next, the image data for each of the windows W1 to W4 written in the image memories 4A to 4D is transferred to the first to fourth image processors 5A to 5A.
Read out to D, and the first to fourth image processors 5
Image data obtained by performing a series of image processing such as filter processing and uniformity processing in A to 5D is obtained. Thus the first
The image data obtained by the fourth image processors 5A to 5D is output to the scattered component removing circuit 6 and also to the correction coefficient generating circuit 8. Then, the correction coefficient generation circuit 8
At, the parameter for removing the scattered component is created and sent to the scattered component removing circuit 6. In response to this, the scattered component removing circuit 6 performs a process of removing the scattered component from the distribution of the energy spectrum of the gamma rays in W3, and the second R
Display the distribution image of I energy spectrum 1
0, and the process of removing the scattered component and the second RI component from the distribution of the gamma ray energy spectrum in W2 is performed, and the distribution image of the first RI energy spectrum is displayed on the display 10. In the present embodiment in which the system operates as described above, the process of setting the energy window, removing the scattered components, and separating the data into two types of RI is performed according to FIG. First, four energy windows W as shown in FIG.
1, W2, W3 and W4 are set (process 1 in FIG. 2).
The detailed setting method will be described later. Here, if the radioisotope of the photopeak on the low energy side is RI1 and the radioisotope of the photopeak on the high energy side is RI2, the photopeak of RI1 is P1 and the photopeak of RI2 is P2 in FIG. . RI1 and RI2 are arbitrary RI
Should be selected and used, for example, Tc-99 as RI1.
I-123 is used as m and RI2. Photoelectric peak is R
Since it is a unique value of I, if RI to be used is decided, P1 and P
The position of 2 is fixed.

Here, the terms low energy subwindow, main window and high energy subwindow are defined. Description will be made with reference to FIG. 13 showing an energy spectrum when one type of RI is used. The regions obtained by dividing the energy spectrum of FIG.
6, the main window 17 and the high energy sub window 18 are called. The main window 17 has an arbitrary width with respect to the energy value of the photoelectric peak according to the resolution of the detector,
For example, it is set to about 20%. The low-energy subwindow 16 and the high-energy subwindow 18 are set to have a narrow width in contact with the low-energy side and the high-energy side of the main window 17, for example, about 3 to 10% of the energy value of the photoelectric peak.

Using the terms low energy subwindow, main window, and high energy subwindow, the setting of the energy window for the energy spectrum when the two types of RI shown in FIG. 3 are used will be described below. W1 is set at the position of the low energy subwindow of RI1. W2 is set at the position of the main window of RI1. However, the boundary of W2 on the low energy side is in contact with W1, but the boundary of W2 on the high energy side is the photoelectric peak of RI2. W3 is set to a main window on the higher energy side than the photopeak of RI2, that is, a position from the photopeak of RI2 to the high energy subwindow of RI2. W4 is set at the position of the high energy subwindow of RI2. These windows can be automatically set by the window level generation circuit 7A by inputting the energy values of the photoelectric peaks of two types of RI administered to the subject. The setting of each window may be manually performed while displaying the energy spectrum on the monitor. For example, the window may be set while confirming it on the monitor using a mouse or the like.

After setting the energy window, data is collected (process 2 in FIG. 2). The scattered radiation component included in W3 of the collected data is estimated (process 3 in FIG. 2). That is, the hatched rectangular portion of the energy spectrum shown in FIG. 4 can be approximated as a scattered ray component included in W3 (rectangular approximation). The area of this rectangular portion is calculated by the following equation 1.

[0016]

[Equation 1] (scattered ray component of W3) = (width of W3) {(area of W4) /
(Width of W4) That is, the height of the rectangle is calculated from W4. The scattered ray component of W3 calculated by Equation 1 is subtracted from W3 to perform scattered ray correction of W3 (process 3 in FIG. 2). The data after the scattering correction of W3 is the hatched portion in FIG. 5, which corresponds to the count on the high energy side half of RI2.

The total count of RI2 can be calculated by doubling the count on the high energy side half of RI2 (process 5 in FIG. 2). This corresponds to the hatched portion of FIG. 6 obtained by folding back the hatched portion of FIG. 5 corresponding to the count of the high energy side half of RI2 to the low energy side.

Therefore, since W2 contains data on the low energy side of RI2, W2 to RI2
The data on the low energy side of is subtracted (process 6 in FIG. 2). This is shown in FIG. 7, where W2 is the total count of RI1 after subtracting the data on the low energy side half of RI2. However, since this includes a scattered ray component, it is estimated and removed.

The scattered radiation component contained in W2 is estimated (process 7 in FIG. 2). That is, the trapezoidal portion with hatching of the energy spectrum shown in FIG. 8 can be approximated as the scattered ray component included in W2 (trapezoidal approximation). The area of this trapezoidal portion is calculated by the following equation 2.

[0020]

[Formula 2] (scattered ray component of W2) = (width of W2) {(area of W1) / (width of W1) + (area of W4) / (width of W4)} / 2 That is, from W1 to a trapezoid The lower side is calculated, and the upper side of the trapezoid is calculated from W4.

The scattered ray component of W2 calculated by Equation 2 is subtracted from W2 to correct the scattered ray of W2 (process 8 in FIG. 2). The data of W2 after scatter ray correction has an energy spectrum as shown in FIG. 9, and RI after scatter ray correction is performed.
Total count of 1.

As described above, this embodiment has two types of R
When I was simultaneously administered, four energy windows were provided to collect data, and the data on the high energy side, which is less affected by scattered radiation, is mainly used, and the R on the high photoelectric peak side is collected.
The data of I is first obtained, and then the data of RI on the lower photopeak side is obtained, whereby two types of RI data are separated. This makes it possible to accurately separate the two types of RI data without increasing the amount of data to be collected.

In the above embodiment, the case where four energy windows are set has been shown, but the present invention is not limited to this. An example of setting five energy windows will be described below. The process flow is as shown in FIG. 2 as in the case of setting four energy windows. First, as shown in FIG. 10, five energy windows W1, W2, W3, W4 and W5 are set (FIG. 2). Processing 1). W1 is set at the position of the low energy subwindow of RI1. W2 is set at the position of the main window of RI1. However, the boundary of W2 on the low energy side is in contact with W1, but the boundary of W2 on the high energy side is RI.
2 photoelectric peak. W3 is set to a main window on the higher energy side than the photopeak of RI2, that is, a position from the photopeak of RI2 to the high energy subwindow of RI2. W4 is set at the position of the high energy subwindow of RI2. W5 is a second high-energy subwindow of RI2 that is in contact with W4 and is provided on the higher energy side.

After setting the energy window, data is collected (process 2 in FIG. 2). The scattered radiation component included in W3 of the collected data is estimated (process 3 in FIG. 2). The hatched trapezoidal portion of the energy spectrum shown in FIG. 11 is approximated as the scattered ray component included in W3. The average value of the count values of W4 and W5 is (W4
Area) / (width of W4), (area of W5) / (width of W5). The average value of the count values of W4 is the upper side of the trapezoid that is hatched. Then, the slope of the energy spectrum of the portions W4 and W5 is calculated, and the count value at the intersection of the straight line having this slope and the boundary line of W2 and W3 is obtained. This is the bottom side of the trapezoid that is hatched. Since the height of the hatched trapezoid is the width of W3, the area of this trapezoid, that is, the scattered ray component contained in W3 can be obtained. After that, the process after the scattered radiation correction of W3 (process 4 in FIG. 2) and subsequent processes are the same as in the case of setting the above-mentioned four energy windows. By setting five energy windows, the scattered radiation correction of W3 can be performed more accurately.

[0025]

According to the present invention, two types of RI can be separated accurately without increasing the amount of data to be handled in a nuclear medicine diagnosis performed by simultaneously administering two types of RI to a subject.

[Brief description of drawings]

FIG. 1 is a system configuration of an embodiment of a nuclear medicine diagnostic apparatus of the present invention.

FIG. 2 is a flowchart showing a separation method of the present invention.

[Fig. 3] Energy window setting (4 energy windows)

FIG. 4 Estimation of scattered radiation in window 3 by rectangle approximation

FIG. 5: Scattered ray correction in window 3

FIG. 6 Calculation of the total number of RI2 counts

FIG. 7: Removal of RI2 component contained in window 2

FIG. 8: Estimation of scattered rays in window 2 by trapezoidal approximation

FIG. 9: Scattered ray correction in window 2

Fig. 10 Energy window setting (5 energy windows)

FIG. 11: Estimation of scattered radiation in window 3 by linear extrapolation

FIG. 12: Energy spectrum with two photopeaks

FIG. 13: Energy window when one type of RI is used

[Explanation of symbols]

 1 Gamma Camera 2 A / D Converter 3 Image Memory Controller 4A to 4D Image Memory 5A to 5D Image Processor 6 Scattering Component Removal Circuit 7 Window Circuit 8 Correction Factor Generation Circuit 9 CPU 10 Display 11 RI1 Photoelectric Peak 12 RI2 Photoelectric Peak 13 energy region 14 energy region 15 energy region 16 low energy subwindow 17 main window 18 high energy subwindow W1 energy window 1 W2 energy window 2 W3 energy window 3 W4 energy window 4 W5 energy window 5 P1 RI1 photoelectric peak P2 RI2 Photoelectric peak

Claims (12)

[Claims] 1. A nuclear medicine diagnostic apparatus comprising means for measuring radiation emitted from two types of radioisotopes administered to a subject and separating the measured data into components of each radioisotope. A nuclear medicine diagnostic apparatus characterized in that a means for separating into components uses a plurality of energy windows. 2. The nuclear medicine diagnostic apparatus according to claim 1, wherein the means for separating the radioisotope component also corrects scattered radiation. 3. The nuclear medicine diagnostic apparatus according to claim 1, wherein four energy windows are used. 4. The energy window is referred to as a first energy window, a second energy window, a third energy window, and a fourth energy window in order from the low energy side, and the radioisotope is referred to as a photopeak. First from the low energy side
Radioisotope of the above, when referred to as a second radioisotope, the second energy window to a predetermined width with respect to the photopeak of the first radioisotope,
The boundary on the high energy side is set to be the photopeak of the second radioisotope, the first energy window is set to a predetermined width in contact with the low energy side of the second energy window, The third energy window is set to a predetermined width in contact with the high energy side of the second energy window, and the fourth energy window is set to a predetermined width in contact with the high energy side of the third energy window. The nuclear medicine diagnostic apparatus according to claim 3, wherein 5. The nuclear medicine diagnostic apparatus according to claim 1, wherein five energy windows are used. 6. The radiation windows are referred to as a first energy window, a second energy window, a third energy window, a fourth energy window and a fifth energy window in order from the low energy side, and the radioactive The isotopes are the first radioisotope and the second in order from the one with the photoenergy peak on the low energy side.
Of the first radioisotope, the second energy window has a predetermined width with respect to the photopeak of the first radioisotope, and the boundary on the high energy side is the second radioisotope. Of the second energy window, the first energy window is set to a predetermined width in contact with the low energy side of the second energy window, and the third energy window of the second energy window is set to A predetermined width in contact with the high energy side is set, a fourth energy window is set in a predetermined width in contact with the high energy side of the third energy window, and the fifth energy window is set to the fourth energy window. The nuclear medicine diagnostic apparatus according to claim 5, wherein the predetermined width is set in contact with the high energy side of the energy window. 7. A radioisotope which measures the radiation emitted from two types of radioisotopes administered to a subject and separates the components of each radioisotope by using a plurality of energy windows for the measurement data. Separation method. 8. The method for separating radioisotopes according to claim 7, wherein the scattered radiation is also corrected. 9. The method for separating radioisotopes according to claim 7, wherein four energy windows are used. 10. A first energy window, a second energy window, a third energy window, and a fourth energy window in order from the low energy side of the energy window.
When the radioisotopes are referred to as a first radioisotope and a second radioisotope in order from the one having a low energy photopeak, the second energy window Is set to have a predetermined width with respect to the photopeak of the first radioisotope, and the boundary on the high energy side is the photopeak of the second radioisotope, and the first energy window is set to the first energy window. The second energy window is set to a predetermined width in contact with the low energy side, the third energy window is set to a predetermined width in contact with the high energy side of the second energy window, and a fourth energy window is set. Is set to a predetermined width in contact with the high energy side of the third energy window. Method of separating Cum isotopes. 11. The method for separating radioisotopes according to claim 7, wherein five energy windows are used. 12. A first energy window, a second energy window, a third energy window, and a fourth energy window in order from the low energy side of the energy window.
Energy window and a fifth energy window, and when the radioisotopes are referred to as a first radioisotope and a second radioisotope in order from the one having a photoelectric peak having a low energy side, The second
Is set to have a predetermined width with respect to the photopeak of the first radioisotope, and the boundary on the high energy side is the photopeak of the second radioisotope. Is set to a predetermined width in contact with the low energy side of the second energy window, and the third energy window is set to the second energy window.
Is set to a predetermined width in contact with the high energy side of the energy window of
7. The predetermined width is set in contact with the high energy side of the energy window of, and the fifth energy window is set in the predetermined width in contact with the high energy side of the fourth energy window. 11. The method for separating radioisotopes according to 11.