JPH08166457A - Nuclear medicine imaging equipment - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the image quality of the reconstructed image by eliminating the influence of scattered radiation. [Structure] A collimator 1, a detector 2 which detects γ-rays incident through the collimator 1 and outputs position signals X and Y and an energy signal Z, and whether or not the energy signal Z is in an energy window. An energy analyzer 3 for detecting, an energy spectrum collecting device 4 for collecting the energy signal Z for each energy, and a control device 7 for shifting the energy window according to the collected energy spectrum are provided.

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 apparatus, and more particularly to a scintillation camera (gamma camera) and a SPECT (Single P
Hoton Emission Computed Tomograph) and other nuclear medicine imaging devices.

[0002]

2. Description of the Related Art A nuclear medicine imaging device such as a scintillation camera detects radiation emitted from the inside of the body when RI (radioisotope) is administered to a subject and accumulated in a specific organ. Emission data is collected to obtain an image. In this case, it is necessary to detect only the radiation from the administered nuclide of interest.
Therefore, generally, an energy analyzer having an energy window corresponding to the energy of radiation from a target nuclide is used to detect only the events in the window and capture the data to construct an image.

However, the radiation emitted from the nuclide in the body is absorbed by the tissues in the body before coming out to the outside, causing Compton scattering. Therefore, if only the event that enters the energy window as described above is detected, the influence of this scattered ray is exerted.

Therefore, various proposals have heretofore been made to correct this scattered radiation.

[0005]

However, there is a problem that the conventional scattered ray correction method cannot effectively remove scattered rays. That is, in the actual clinical practice in the medical field, there are various absorption / scattering states in the patient's body and background radiation states, so that the energy spectrum varies.

In view of the above, the present invention has been improved so as to effectively remove the influence of scattered rays in response to actual clinical absorption / scattering and background conditions and improve the contrast and resolution of reconstructed images. Another object of the present invention is to provide a nuclear medicine imaging device.

[0007]

In order to achieve the above object, in a nuclear medicine imaging apparatus according to the present invention, a radiation detecting means for outputting a position signal and an energy signal of incident radiation, and the above energy signal are Energy analysis means for determining whether or not it is within a predetermined energy window, means for obtaining the energy spectrum by collecting the energy signals, and adjusting the energy window of the energy analysis means according to the energy spectrum. It is characterized by having a control means.

[0008]

Since the energy signal output from the radiation detecting means is collected to obtain the energy spectrum, this energy spectrum is for the entire field of view of the radiation detecting means. Since the energy window of the energy analysis means is adjusted according to this energy spectrum, the energy window is adjusted uniformly over the entire field of view of the radiation detection means. In this way, the energy window of the entire field of view is controlled from the energy spectrum of the entire field of view, and the effect of the scattering is effectively removed according to the state of the scattering of the actual subject, although the configuration is extremely simple. can do. Therefore, with a simple structure, it is possible to improve the contrast and resolution of the reconstructed image and obtain a radiation image with excellent image quality.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a gamma camera according to an embodiment of the present invention, which includes a collimator 1, a detector 2, and an energy analyzer 3. These are similar to ordinary gamma cameras. Furthermore, the energy spectrum collection device 4 and the control device 7 for controlling the energy window of the energy analyzer 3 according to the collected energy spectrum are provided.

The collimator 1 passes only the γ-rays emitted from the nuclide injected into the body of the subject 8 in all directions around the detector 2, which is perpendicular to the detector 2. Detector 2
Although omitted in the figure, a plate-shaped scintillator that emits light upon incidence of radiation, a large number of photoelectric converters arranged on the back surface of the scintillator, and a signal processing circuit that processes output signals of these photoelectric converters are included. Including. When γ-rays are incident and light is generated, the light is incident on each photoelectric converter and an output is generated from each photoelectric converter.The output from each photoelectric converter is the distance from the light emitting point to their incident surface. It corresponds to. Therefore, in the signal processing circuit, the outputs of the respective photoelectric converters are weighted and added according to the position to obtain the position signals X and Y in the two directions (X and Y directions). Further, this signal processing circuit outputs the peak value of the signal obtained by adding the outputs of all the photoelectric converters as the energy signal Z. This is because the crest value of the signal obtained by adding the outputs of all the photoelectric converters corresponds to the energy of the γ-ray that is incident on the detector 2 and emitted.

The energy signal Z is determined by the energy analyzer 3 to determine whether it is within a predetermined energy window, and when it is, an unblank signal (UNB) is output. Specifically, this energy analyzer 3 consists of two comparators,
The two reference signals and the energy signal Z are compared to determine if the energy signal Z lies between the two reference signals.

When an unblank signal is output from the energy analyzer 3, γ-rays from the nuclide to be detected, which is administered to the subject 8, is incident, and this is detected. The position signals X and Y of (1) are fetched into an image collecting memory or an image display device (not shown), and the position is incremented by +1 at the position determined by the position signals X and Y. In this way, the image of the nuclide is reconstructed.

On the other hand, in this embodiment, the energy signal Z
Is also sent to the energy spectrum collector 4. This energy spectrum collector 4 is, for example, A
It is composed of a / D converter 5 and a data collection memory 6 addressed by its output. The energy signal Z is converted into a digital signal by the A / D converter 5, and the address of the data collection memory 6 designated by the digital signal is incremented by +1. Here, since such data collection is performed for all energy signals Z regardless of the position signals X and Y, counting is performed in the data collection memory 6 for each incident γ-ray energy in the entire field of view of the detector 2. Will be
An energy spectrum as shown in FIGS. 2 and 3 is obtained.

When the energy spectra are collected in this manner, the energy spectrum as shown in FIG. 2 is obtained in an ideal state where there is no (or little) scattering, and the energy spectrum shown in FIG. Become. That is, when there is no scattering, as shown in FIG. 2, the spectrum has only the energy peak P1 of γ-rays from the nuclide to be detected, whereas when there is a large amount of scattering, the target nuclide as shown in FIG. Peak P1
In addition to the above, a Compton scattering peak P2 appears.

In the absence of scattering, the energy window W
As shown in FIG. 2, if the width is set to about 10% above and below the peak P1 of the target nuclide, only γ rays from the target nuclide can be detected. On the other hand, when there is a large amount of scattering, the influence of Compton scattering is also mixed in the vicinity of the peak P1 as a signal component as shown by the dotted line, so the energy window W1 at this time is If the energy window W is set to be the same as that of the energy window W, the component of scattered radiation is mixed and the image quality of the image is deteriorated.

In this embodiment, since an actual clinical energy spectrum as shown in FIG. 3 is obtained, the control device 7 refers to this and moves the energy window in the energy analyzer 3 from W1 to W2 to the higher side ( Specifically, the reference signals given to the two comparators forming the energy analyzer 3 are changed).

For example, the percentage of shifting the energy window to the higher side is S (%), the energy of P1 is P1e (keV), and the energy of P2 is P2e.
(KeV), P1 peak count is P1c (count), P2 peak count is P2c (count), K
Is a constant, S = (P2c / P1c) / [K / {(P1e-P2e)
/ P1e}] is used to calculate S. That is, the control device 7 reads the energies and counts of P1 and P2 from the energy spectrum collecting device 4 and performs this calculation, and controls the energy analyzer 3 according to the obtained S to shift the energy window by S (%). .

As described above, since the shift amount of the energy window is obtained by referring to not only the energy and the count of the peak P1 of the target nuclide but also the energy and the count of the peak P2 of Compton scattering, the shift amount of the actual scattering line is obtained. It is possible to collect images with the effects removed more appropriately. Therefore, the image thus obtained has excellent image quality with good contrast and resolution.

In the above description, the source of one nuclide has been described, but the same applies to a source using two or more nuclides. In the case of two or more nuclides, the energy of the peak value and the count are referred to for the respective energy peaks of those nuclides, and the energy window is adjusted accordingly.

In addition, it goes without saying that the specific configuration can be variously modified without departing from the spirit of the present invention.

[0021]

As described in the above embodiments, according to the nuclear medicine imaging apparatus of the present invention, it is possible to determine the most appropriate energy window according to the actual state of scattered rays. Can be efficiently removed, and as a result, the contrast and resolution of the reconstructed image can be improved, and a radiation image with excellent image quality can be obtained. Moreover, since the energy window for the entire visual field is changed according to the energy spectrum for the entire visual field, the configuration is simple and a large effect can be obtained with the simple configuration.

[Brief description of drawings]

FIG. 1 is a block diagram of a gamma camera according to an embodiment of the present invention.

FIG. 2 is a graph showing an energy spectrum in a state of little scattering.

FIG. 3 is a graph showing an energy spectrum in a state where there is a large amount of scattering.

[Explanation of symbols]

 1 Collimator 2 Detector 3 Energy Analyzer 4 Energy Spectrum Collection Device 5 A / D Converter 6 Data Collection Memory 7 Control Device 8 Subject

Claims (1)

[Claims] 1. A radiation detecting means for outputting a position signal and an energy signal of incident radiation, an energy analyzing means for judging whether or not the energy signal is within a predetermined energy window, and the energy signal. And a control means for adjusting the energy window of the energy analysis means in accordance with the energy spectrum, and a control means for adjusting the energy window.