JP2004053494A - Nuclear medical diagnosis apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a SPECT (single photon emission computed tomography) image for scattered rays without collecting TCT (transmission computed tomography) data by a transmission generator. <P>SOLUTION: On the basis of projection data obtained by detecting gamma rays emitted from RI (radioactive isotope) administered to a subject, the SPECT image is reconstructed at a reconstruction device 300. Transmission CT projection data are prepared from an X-ray CT image of the same subject obtained about the part approximately equal to that of the SPECT image. The transmission CT projection data are subtracted from the SPECT image. Thus, the scattered ray correction device 400 is provided, which performs the scattered ray correction. Accordingly, the time required for performing the inspection is shortened, and the burden on the subject and the medical staff is relieved. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nuclear medicine diagnostic apparatus, and more particularly to a nuclear medicine diagnostic apparatus that corrects scattered radiation caused by a subject during a SPECT examination to reduce image degradation and improve diagnostic accuracy.
[0002]
[Prior art]
A drug labeled with a radioisotope (hereinafter abbreviated as RI) is administered into a subject, and radiation (gamma rays) emitted from the RI is detected and measured outside the subject, whereby the RI is measured. A nuclear medicine diagnostic apparatus for imaging the state of distribution in a subject has been clinically used. Further, recently, a SPECT (Single Photon Emission Computed Tomography) apparatus capable of observing a state of a three-dimensional distribution of an RI in a subject has attracted attention.
By the way, gamma rays emitted from RI in a subject are usually affected by attenuation caused by Compton scattering in the subject, and gamma ray projection data detected and measured outside the body is not necessarily the subject. It did not accurately reflect the RI distribution within. In order to remove the influence of such scattered radiation, a scattered radiation correction method has conventionally been proposed, and the method is roughly classified into a TEW (Triple Energy Window) scattered radiation correction method and an analytical method.
The TEW method is a method in which three windows are set for one energy spectrum, the scattered radiation component included in the main window is calculated from the Compton region, and correction is performed by subtracting this. The analytic method is a method of calculating a projection image with respect to scattered radiation included in projection data using a point spread function or the like, and subtracting the calculated image from a measurement image, and corresponds to the CS (Convolution Subtraction) method. In addition, among CS methods, scattered radiation correction by a TDCS (Transmission Dependent Contraction Subtraction) method using a transmission of the subject has recently attracted attention in order to improve the correction accuracy of the subject for the non-uniform absorber.
Conventionally, in order to carry out the TDCS method, TCT data based on transmission computed tomography (TCT) using a combination of a SPECT apparatus or the like and a transmission generator is obtained, and a gamma in the subject is obtained. The absorption distribution of the line was being examined.
[0003]
[Problems to be solved by the invention]
However, installing a transmission generator only for scattered radiation correction by the TDCS method has a drawback in terms of investment efficiency. At present, in Japan, it is difficult to use the transmission source because it is only allowed to use a closed source as a transmission generator, and the closed source is expensive. Further, depending on the nuclide, it is necessary to separately collect TCT data, and it takes time for the inspection, which is a disadvantage.
In order to solve such problems, the present invention rarely conducts a recent nuclear medicine diagnosis by a single examination of only nuclear medicine using a SPECT apparatus or the like, and in most cases, an X-ray CT examination using an X-ray CT apparatus In view of the fact that is used in combination, X-ray CT transmission data is created from an X-ray CT image, and this is used to correct scattered radiation.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 collects radiation detection means for detecting radiation emitted from a radiation isotope administered to a subject, and collects radiation projection data detected by the radiation detection means. Image reconstruction means for reconstructing a nuclear medicine image based on the collected radiation projection data; and an X-ray of the same subject obtained for a site substantially equal to the nuclear medicine image reconstructed by the image reconstruction means. Transmission CT projection data creation means for creating transmission CT projection data from a CT image, and nuclear medicine reconstructed by the image reconstruction means using the transmission CT projection data created by the transmission CT projection data creation means A scattered radiation correction unit for performing scattered radiation correction on the image. That.
[0005]
Further, according to a second aspect of the present invention, in the nuclear medicine diagnostic apparatus according to the first aspect, the transmission CT projection data creating means adjusts a position of the X-ray CT image to a position of the nuclear medicine image. Positioning means, attenuation map converting means for converting the X-ray CT image aligned by the positioning means into a gamma ray attenuation coefficient distribution image, and gamma ray attenuation coefficient converted by the attenuation map converting means It is characterized by comprising sinogram data creating means for creating sinogram data from a distribution image, and format conversion means for converting sinogram data created by the sinogram data creating means into the same format as the radiation projection data.
[0006]
Thereby, by using the X-ray CT image obtained by the X-ray CT imaging performed in conjunction with the normal SPECT inspection, the TCT data by the transmission generator can be separately obtained without changing the scattered radiation correction algorithm by the TDCS method. It is possible to perform scattered radiation correction on the SPECT reconstructed image without collecting.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a nuclear medicine diagnostic apparatus according to the present invention will be described in detail with reference to FIGS.
FIG. 1 is a system diagram for explaining a configuration of an embodiment of a nuclear medicine diagnostic apparatus according to the present invention.
As shown in FIG. 1, a nuclear medicine diagnostic apparatus according to the present invention includes a radiation detector 100 that detects gamma rays emitted from RI in a subject P, and projects an electric signal output from the radiation detector 100. A data collection device 200 for collecting as data, a reconstruction device 300 for reconstructing a three-dimensional distribution of RI present in the subject P as an image based on the projection data collected by the data collection device 200, and a reconstruction device A scattered radiation correction device 400 for correcting the effect of scattered radiation generated in the subject P on the image reconstructed by the 300 (hereinafter, referred to as a SPECT reconstructed image). A display device 500 for displaying the corrected SPECT reconstructed image is provided.
[0008]
The radiation detector 100 includes a collimator 110, a scintillator 120, and a photoelectric conversion unit 130. These are formed of a radiation shielding material such as lead, except for the opening side of the collimator 110 (the side facing the subject P). Being held in the case. Further, the radiation detector 100 has a structure in which the opening surface side has a circular or rectangular shape and is supported by an arm (not shown) integrally with the case, and is rotated around the subject P in accordance with the operation of the arm. ing.
The collimator 110 has a large number of, for example, honeycomb-shaped openings 112 arranged two-dimensionally by a partition wall 111 made of a radiation shielding material such as lead. It is roughly divided into fan beam collimators. The parallel collimator is formed such that the axis of the opening 112 is perpendicular to the scintillator 120 located at the subsequent stage of the collimator 110. It is formed to be vertical. On the other hand, in the fan beam collimator, the axis of the opening 112 is perpendicular to the body axis of the subject P, but is inclined toward the center of the subject P with respect to a horizontal axis orthogonal to the body axis. It is formed so as to focus along the body axis.
The scintillator 120 is made of, for example, a NaI crystal, receives a gamma ray radiated from the inside of the subject P and reaches through the opening 112 of the collimator 110, and converts the gamma ray into light. The light converted by the scintillator 120 is further converted into an electric signal by the photoelectric conversion unit 130. In the photoelectric conversion unit 130, for example, photoelectric conversion members such as a photomultiplier tube for converting an optical signal into an electric signal are arranged in a matrix, and the output of the photoelectric conversion member is supplied to a position calculation circuit (not shown). It is supposed to be. Therefore, in the position calculation circuit, the light emission position in the scintillator 120, that is, the subject P is determined by determining the intensity of the optical signal emitted from the scintillator 120 by each photoelectric conversion member. It detects information about the radiation position in the interior.
Although only one radiation detector 100 is shown in FIG. 1, it goes without saying that two or more radiation detectors may be provided as necessary as a nuclear medicine diagnostic apparatus. Further, a semiconductor detector may be provided instead of the scintillator 120 and the photoelectric conversion unit 130 of the radiation detector 100.
[0009]
Next, the data collection device 200 receives the electric signal output from the radiation detector 100 and collects it as radiation projection data. When the aperture 112 of the collimator 110 provided in the radiation detector 100 is a parallel collimator formed vertically toward the scintillator 120, the projection data collected by the data collection device 200 is parallel beam data. In this case, the projection data collected by the data collection device 200 is supplied to the reconstruction device 300 as it is. Therefore, the reconstruction device 300 reconstructs a tomographic image related to the three-dimensional distribution of RI existing in the subject P based on the collected projection data.
However, the axis of the opening 112 of the collimator 110 provided in the radiation detector 100 is perpendicular to the body axis of the subject P, but the subject P is perpendicular to the horizontal axis perpendicular to the body axis. In the case of a fan beam collimator formed so as to be inclined toward the center of the body and focused along the body axis, the projection data collected by the data collection device 200 is fan beam data. The conversion device provided inside or separately from 200 performs a process of converting the fan beam data into the parallel beam data. Here, the projection data converted into the parallel beam data is supplied to the reconstruction device 300. Therefore, the reconstructing apparatus 300 reconstructs a tomographic image (SPECT reconstructed image) related to the three-dimensional distribution of RI existing in the subject P based on the projection data converted into the parallel beam data.
[0010]
The SPECT reconstructed image obtained from the reconstruction device 300 is supplied to the scattered radiation correction device 400. The scattered radiation correction device 400 includes an image capturing unit 410, a positioning unit 420, an attenuation map conversion unit 430, a sinogram data creation unit 440, a format conversion unit 450, and a scattered radiation correction unit 460.
Prior to the correction of the scattered radiation, the image capturing unit 410 converts the SPECT reconstructed image subjected to the scattered radiation correction reconstructed by the reconstruction device 300 and the X-ray CT image to provide the scattered radiation correction data. It is something to take in. That is, the SPECT reconstructed image that is reconstructed by the reconstructing apparatus 300 and is about to undergo scattered ray correction from now on, and the same subject P from which the SPECT reconstructed image is obtained, a portion substantially equal to the SPECT reconstructed image And an X-ray CT image captured in advance by the X-ray CT apparatus 600 into the image capturing unit 410.
Next, the alignment unit 420 aligns the SPECT reconstructed image captured by the image capturing unit 410 with the X-ray CT image. In this alignment, the X-ray CT image is three-dimensionally aligned with respect to the SPECT reconstructed image so as to have the same number of slices and the same position and the same matrix size for each slice. For such a method of alignment, an automatic method or a method in which an operator manually performs the operation while viewing an image can be adopted as appropriate. Is omitted.
[0011]
The attenuation map conversion unit 430 adjusts the X-ray CT image aligned with the SPECT reconstructed image by the alignment unit 420 to a distribution image of a line attenuation coefficient of a gamma ray (this is referred to as an attenuation map). . That is, in the X-ray CT image, while the CT value of water is 0 and the CT value of air is 1024, for example, when the RI is Tc-99m of 140 keV, the line attenuation coefficient u of the gamma ray is Since it is 0 for air and 0.15 [1 / cm] for water, the CT value for each pixel of the X-ray CT image is converted into a linear attenuation coefficient u to create an attenuation map. As this conversion method, linear conversion by linear approximation or the like is adopted, but the conversion method is not the subject of the present invention, and any well-known conversion method may be used, and therefore the description thereof will be omitted. FIG. 2 shows an attenuation map for 16 slices of the head of the subject P as an example of the created attenuation map. However, the number of the attenuation map is usually larger when actually used.
[0012]
Next, the sinogram data creation unit 440 creates sinogram data from the attenuation map converted and created by the attenuation map conversion unit 430. The sinogram is obtained by developing data collected by scanning with an X-ray CT apparatus in two dimensions in the channel direction and the projection direction of the detector and displaying the data in shades according to the values of each data. The creation unit 440 creates sinogram data for the attenuation map obtained by converting the CT value into the linear attenuation coefficient u so that the sampling start angle, the sampling angle, and the like are matched with the projection data that forms the SPECT reconstructed image. FIG. 3 shows an example of a sinogram created corresponding to each of the attenuation maps for 16 slices shown in FIG.
Further, the format conversion unit 450 rearranges the sinogram data created by the sinogram data creation unit 440 and converts the sinogram data into the same format as the SPECT projection data, thereby creating transmission CT projection data. FIG. 4 shows an example of a transmission CT projection image created corresponding to each of the sinograms shown in FIG. 3, which is obtained in order to examine the absorption distribution of radiation in the subject P in the related art. TCT data.
[0013]
Therefore, the scattered radiation correction unit 460 performs a process of subtracting the transmission CT projection image corresponding to the TCT data created by the format conversion unit 450 from the SPECT reconstructed image reconstructed by the reconstruction apparatus 300, and performs SPECT reconstruction. Scattered radiation correction by the TDCS method is performed on the constituent image. At this time, the scattered radiation constant image and the convolution function are obtained. The method of obtaining the scattered radiation constant image and the convolution function is the same as in the case of the TDCS method. It can be handled simply by changing the parameters. Further, when the scattered radiation constant image and the convolution function are obtained, scattered radiation correction is performed by calculating a successive approximation expression shown as the following expression (1).
g ⁿ _true (x, y) = g _obs (x, y) −g ^n-1 _ct (x, y) *
f (x, y) * k (x, y) (1)
Here, g ⁿ _true (x, y) is a SPECT projection image in which scattered radiation has been corrected,
_gobs (x, y) is the SPECT projection data,
g ^n-1 _ct (x, y) is transmission CT projection data;
f (x, y) is a convolution function,
k (x, y) is a scattered radiation constant. The zero-order successive approximation is the same as SPECT projection data without scattered radiation correction.
FIG. 5 shows an example of the SPECT projection image in which the scattered radiation has been corrected in this way, corresponding to the transmission CT projection image shown in FIG. That is, the SPECT projection image obtained by correcting the scattered radiation obtained from the scattered radiation correction unit 460 is displayed in a multi-format format of 16 slices as shown in FIG. 5, for example, or an image of an arbitrary slice is extracted and displayed. Displayed on device 500.
Although the present invention has been described for the case where the scattered radiation correction is performed on the SPECT reconstructed image by the TDCS method, the present invention is not limited to the TDCS method.
[0014]
【The invention's effect】
As described in detail above, according to the present invention, by using an X-ray CT image obtained by X-ray CT imaging usually performed in conjunction with a SPECT inspection, the algorithm of scattered radiation correction by the TDCS method is changed. The scattered radiation correction for the SPECT reconstructed image can be performed without collecting the TCT data separately by the transmission generator. Therefore, the time required for the examination can be reduced, the burden on the subject and the medical staff can be reduced, and the efficiency of diagnosis can be improved.
[Brief description of the drawings]
FIG.
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a system diagram shown to explain a configuration of an embodiment of a nuclear medicine diagnostic apparatus according to the present invention.
FIG. 2
It is explanatory drawing which showed an example of the attenuation map which converted the X-ray CT image.
FIG. 3
FIG. 3 is an explanatory diagram showing an example of a sinogram created corresponding to each of the attenuation maps of FIG. 2.
FIG. 4
FIG. 4 is an explanatory diagram showing an example of a transmission CT projection image created corresponding to each of the sinograms in FIG. 3.
FIG. 5
FIG. 5 is an explanatory diagram showing an example of a SPECT projection image in which scattered radiation has been corrected corresponding to the transmission CT projection image of FIG. 4.
[Explanation of symbols]
REFERENCE SIGNS LIST 100 radiation detector 110 collimator 120 scintillator 130 photoelectric conversion unit 200 data collection device 300 reconstruction device 400 scattered radiation correction device 410 image capture unit 420 positioning unit 430 attenuation map conversion unit 440 sinogram data creation unit 450 format conversion unit 460 scattering Line correction unit 500 Display device 600 X-ray CT device

Claims (2)

Radiation detection means for detecting radiation emitted from the radioisotope administered to the subject,
Image reconstruction means for collecting radiation projection data detected by the radiation detection means and reconstructing a nuclear medicine image based on the collected radiation projection data,
Transmission CT projection data creation means for creating transmission CT projection data from an X-ray CT image of the same subject obtained for a site substantially equal to the nuclear medicine image reconstructed by the image reconstruction means;
Scattered radiation correction means for performing scattered radiation correction on the nuclear medicine image reconstructed by the image reconstruction means using the transmission CT projection data created by the transmission CT projection data creation means. Nuclear medicine diagnostic equipment. The transmission CT projection data creating means includes:
Alignment means for adjusting the position of the X-ray CT image to the position of the nuclear medicine image;
Attenuation map conversion means for converting the X-ray CT image aligned by the alignment means into a gamma ray attenuation coefficient distribution image;
Sinogram data creating means for creating sinogram data from the attenuation coefficient distribution image of the gamma ray converted by the attenuation map conversion means,
2. The nuclear medicine diagnostic apparatus according to claim 1, further comprising format conversion means for converting the sinogram data created by the sinogram data creation means into the same format as the radiation projection data.

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