JP2001324568A - Gamma camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gamma camera that can detect gamma rays radiating from a wide radioisotope(RI) source with high sensitivity when revolving a detector around a body axis. SOLUTION: When a detector is revolved around a body axis, via a fan beam collimator 4 and a parallel collimator 3 respectively disposed in a body axis direction and in a slicing direction, a scintillator 5 detects gamma rays from an RI source 10 in a subject 9 on a bed 11, and a plurality of photomultiplier tubes 6 capture a position signal and an energy signal of the gamma rays. The three-dimensional data obtained from the fan beam collimator 4 are subjected to the Fourier rebinning method that rearranges them into two-dimensional multilayer data in the same state as if measured by a parallel collimator, before normal reconstruction. The sensitivity can be thus improved from that of an existent parallel collimator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma camera, and more particularly, to rotating a two-dimensional detector around a body axis to collect data on RI distribution in the body, and to obtain a plurality of slices at a time along the body axis. The present invention relates to a detector camera rotating SPECT apparatus capable of obtaining a tomographic image.

[0002]

2. Description of the Related Art With the advancement of X-ray CT and the development of computers, a gamma ray detector equipped with a collimator is rotated around a body axis to utilize gamma rays emitted from the body.
PECT (Single Photon emissi)
on CT) devices have been developed, and RI tomographic images of the inside of the body can be obtained. Since the SPECT apparatus rotates the two-dimensional detector around the body axis, projection data of a plurality of slices can be collected and reconstructed at once, and three-dimensional data can be easily formed. SPECT images are obtained by collecting functional images obtained by accumulating radiopharmaceuticals, and performing diagnosis in combination with morphological images of MRI and X-ray CT.

FIG. 4 shows a system configuration of a SPECT apparatus. The SPECT apparatus includes a bed 11 on which the subject 9 is placed,
A detector 13 that rotates around the body axis of the subject 9 to detect γ-rays from the subject 9, a stand 14 that holds and rotates the detector 13, and a camera that captures an output signal from the detector 13 A console 15, a camera I / F 16 for sending its output to the computer, an ECT controller 17 for controlling the rotation of the detector 13 from the stand 14,
An ECT I / F 18 that sends a signal from a computer to an ECT controller 17; a CPU 19 that collects and processes data of γ-rays input from the detector 13 via the camera console 15 and the camera I / F 16; , An image / graph memory 21 for reconstructing and storing the captured gamma ray data in the CPU 19, a keyboard 24 for inputting necessary commands from the outside to the computer, and an RI tomographic image of the subject 9. It is composed of a color display 22 for displaying an image, and a character display 23 for displaying each necessary command, condition, data and the like with a character.

The gamma rays emitted from the tomographic plane of the subject 9 are measured by a detector 13 arranged in a plane including the tomographic plane, and the measurement data is, as shown in FIG. The data is collected as a series of data indicating the detector position t and the count rate at each line emission direction θ. This corresponds to the data of the projection 12 in the θ direction of the distribution of RI in the subject 9. Reconstruction of the RI distribution from the obtained data of many projections 12 uses the same method as CT. To determine the direction θ of the γ-ray, the detector 13
A collimator is used. The position t is determined using a position detection type detector having a scintillator and a plurality of photomultiplier tubes.

FIG. 6 shows the structure of the detector 13 of the gamma camera. (A) shows a cross section of the subject 9 in the body axis direction, and (b) shows a cross section of the subject 9 viewed from the cross section direction. The detector 13 includes a lead shielding housing 7 that shields γ-rays, a collimator (a parallel collimator 3 in the body axis direction, and a fan beam collimator 4 in the cross-sectional direction), a scintillator 5, and a plurality of PMs.
It comprises a T (photomultiplier tube) 6, a preamplifier, a high voltage circuit, and a position calculation circuit (not shown). This configuration is called an Anger type camera. The principle is
Gamma rays from the RI source 10 of the subject 9 enter the scintillator 5 via the collimator, and emit light at that position. The distance from the light emitting point to each PMT 6 is different, and the output signal of each PMT 6 is different accordingly. Thus, the position of the light emitting point is detected and used as a position signal. This is a value proportional to the energy of the γ-ray. This is an energy signal.
These signals are corrected for spatial linearity and energy characteristics, and are reconstructed.

The collimator has a low energy of 160 keV or less, a medium energy of up to 300 keV,
For high energy of keV or more. In addition, according to the purpose of medical treatment, a parallel hole type having a hole perpendicular to the detector 13, a converging type for reducing a large organ,
There are a diverging type and a pinhole type that enlarge small organs, and a slant hole type that collects γ-rays incident from an oblique direction on the detector surface. Since the sensitivity and resolution differ from each other, they are selected according to the purpose of inspection. And, in addition to the detector of one type, 2 to increase the sensitivity
There is also a combination of four. In order to improve the resolution, a device using an elliptical orbit rotation, a slant hole collimator, or the like is used.

[0007]

The conventional gamma camera is constructed as described above.
In the PECT measurement, a parallel collimator 3 having a wide field of view has been used. However, recently, as shown in FIG. 6B, a fan beam collimator 4 that can collimate in a fan shape only in the cross-sectional direction of the subject 9 is used to increase the sensitivity. However, if the focal length of the fan beam is short, a part of the field of view of the RI source 10 of the subject 9 may be lost, so that a fan beam having a long focal length is used. Although the parallel collimator 3 does not lack the field of view of the RI source 10, the fan beam collimator 4
The sensitivity is lower than that of. On the other hand, although the fan beam collimator 4 has high sensitivity, there is a problem that the field of view is lacking.

The present invention has been made in view of such circumstances, and rotates a gamma ray detector provided with a collimator around a body axis to radiate from a field of view of a wide RI source distributed in the body. An object of the present invention is to provide a gamma camera capable of detecting a line with high sensitivity.

[0009]

In order to achieve the above object, a gamma camera according to the present invention uses a single photon,
A gamma camera that can collect data by rotating a two-dimensional detector around the body axis and obtain tomographic images along the body axis of a plurality of slices at once, radiating the distribution of I in a fan shape in the body axis direction A fan beam collimator for collecting gamma rays to be emitted, a parallel collimator for collecting gamma rays emitted in parallel to the body axis in a direction perpendicular to the body axis, a detector for detecting gamma rays via both of the collimators, and data for processing signals from the detector A processing unit, wherein the data processing unit rearranges the three-dimensional data obtained through the fan beam collimator rotating about the body axis into two-dimensional multilayer data in the same state as when measured by a parallel collimator. The image is reconstructed using the rebinning method.

[0010] The gamma camera of the present invention is configured as described above, and can detect a field of view with high sensitivity using a fan beam collimator in the body axis direction.
A wide field of view can be detected using a parallel collimator in the rotating section direction. In the fan beam collimator in the body axis direction, gamma rays are incident on the detector across each slice plane in the cross section direction, and the sensitivity in the body axis direction is higher than that of the conventional parallel collimator. However, since it cannot be calculated by the normal image reconstruction method, the Fourier-Lebinning method is used here, and the three-dimensional data obtained through the fan beam collimator is converted into two-dimensional multilayer data in the same state as when measured by the parallel collimator. After rearrangement, normal reconstruction is performed. On the other hand, the field of view narrows in the body axis direction, but with a normal gamma camera there is about 40 cm,
Since it may be about 15 cm for the heart, it can be used without any problem.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a gamma camera according to the present invention will be described with reference to FIG. FIG. 1 shows a cross-sectional structure of a detector 13 of the present gamma camera.
(B) shows a cross section viewed from the slice direction. The detector 13 of the gamma camera includes a lead shielding housing 7 for shielding γ-rays, a collimator (a fan beam collimator 4 in the body axis direction, and a parallel collimator 3 in the slice direction).
), A scintillator 5, a plurality of PMTs (photomultiplier tubes) 6, a preamplifier, a high voltage circuit, and a position calculation circuit (not shown). Then, around the body axis of the subject 9 having the RI source 10 on the bed 11,
The gamma detector 13 rotates, and projection data of a plurality of slices can be collected at a time and reconstructed to form three-dimensional data. This gamma camera differs from the conventional gamma camera shown in FIG. 6 in the following points. First, the arrangement directions of the fan beam collimator 4 and the parallel collimator 3 are different. The conventional one arranges the parallel collimator 3 in the body axis direction,
Although the fan beam collimator 4 is arranged in the slice direction, this gamma camera rotates the collimator by 90 degrees, arranges the fan collimator 4 in the body axis direction, and arranges the parallel collimator 3 in the slice direction. .

Next, an image reconstruction method is different. In the conventional method, each acquired projection data of the slice plane is converted into an X-ray CT.
It is reconstructed by using the convolution back projection (CBS) method used in the device or the like, or a modification thereof. In other words, two operations of convolution (convolution) operation and back projection (back projection) operation
Image reconstruction is performed in two stages. As a result, each tomographic image could be obtained. However, in this gamma camera, since the fan beam collimator 4 is set in the body axis direction, as shown in FIG. , At an angle of θ with respect to the vertical section. That is, it is information on a line of an angle crossing the point A of the slice plane 8a, the point B of the slice plane 8b, and the point C of the slice plane 8c. The data of the point P incident obliquely is
Two-dimensional slice plane in the same state as measured by the parallel collimator, here, slice plane 8a, slice plane 8
b, an operation of rearranging the slice plane 8c is performed. Here, a PET (Positron emission) that reconstructs a three-dimensional image using the generation of a pair of gamma rays (two photons) generated when the positron (positron) disappears.
on CT) using the Fourier Rebinning method.

FIG. 3 shows a Fourier-Lebinning method (FOR
The processing procedure of E method) is shown. In the three-dimensional acquisition, the simultaneous coefficient between different rings is also measured.
² sinograms are obtained. These data are p
It is a set of sinograms represented by (s, φ, z, δ = tan (θ)). Where s is the coordinates of the projection data, φ
Represents the projection angle, z represents the axial center coordinate of the Line of Response, and θ represents the inclination angle. 2 in ± θ direction
Create a 360 degree sinogram from the sinograms
s, phi, those subjected to three-dimensional Fourier transform p for _{z (ω, k, ω z} , δ) When, following relation holds.

(Equation 1) Using this relation, the Fou of the sinogram in the ± θ direction
It can be accurately replaced with a rier transform.

3D image reconstruction processing using FORE
The order is as follows. (1) Two-dimensional Fourier transform of parallel sinogram
initialize. P_m(Ω, k) = 0, m = 1, 2,..., 2
N-1. (2) Sinogram obtained by three-dimensional collection
Dimension Fourier transform, | ω |> ω_lim, | K |
> K_limCan be obtained by z ′ = z−kδ / ω
P near z '_m(Ω, k). (3) δ <δ
_lim, That is, sinogram with small tilt angle
Is | ω |> ω _lim, | K |> k_limData of z
Nearby P_m(Ω, k). (4) All θ directions
After normalizing and adding the sinograms of
_m(Ω, k) is subjected to two-dimensional Fourier inverse transformation.
(5) Obtained parallel sinogram p_m(S, φ), m =
, 2N-1 are reconstructed into a two-dimensional image. above
The data of point P obliquely incident is parallelized using the method
2D slice in the same state as measured by collimator
Plane, here, slice plane 8a, slice plane 8b,
An operation of rearranging the chair surface 8c is performed. And sort
Image reconstruction using a normal parallel collimator.
Now.

[0015]

The gamma camera of the present invention is constructed as described above, uses a fan-beam collimator in the body axis direction, and measures three-dimensional data obtained therefrom by a Fourier-Lebinning method with a parallel collimator. Since the data is rearranged into the same state as the two-dimensional multi-layer data and then the normal reconstruction is performed, the sensitivity is improved as compared with the conventional parallel collimator. Can be detected. In a normal gamma camera, the focal length of the fan beam collimator is about 40 cm, and for a heart, it is 15 cm.
m, so there is no problem of visual field in the body axis direction.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a gamma camera of the present invention.

FIG. 2 is an explanatory diagram for converting data obtained by a fan beam collimator of the gamma camera of the present invention into the same state measured by a parallel collimator.

FIG. 3 is a diagram showing a processing procedure of data obtained by the gamma camera of the present invention by a Fourier-Levinning method.

FIG. 4 is a diagram showing a configuration of a SPECT apparatus.

FIG. 5 is a diagram for explaining the principle of a SPECT apparatus.

FIG. 6 is a diagram showing an arrangement of a detector having a fan beam collimator of a conventional SPECT apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 ... Parallel collimator 4 ... Fan beam collimator 5 ... Scintillator 6 ... PMT 7 ... Lead shielding case 8a, 8b, 8c ... Slice plane 9 ... Subject 10 ... RI source 11 ... Bed 12 ... Projection 13 ... Detector 14 ... Stand 15 Camera Console 16 Camera I / F 17 ECT Controller 18 ECT I / F 19 CPU 20 Magnetic Disk 21 Image / Graph Memory 22 Color Display 23 Character Display 24 Keyboard

Claims (1)

[Claims] 1. A gamma camera capable of acquiring data by rotating a two-dimensional detector around a body axis using a single photon and rotating a two-dimensional detector around the body axis to obtain a tomographic image of a plurality of slices along the body axis at a time. A fan beam collimator that collects gamma rays radiating like a fan in the body axis direction, a parallel collimator that collects gamma rays radiating parallel to the body axis, and a detector that detects gamma rays via both collimators, A data processing unit for processing a signal from the detector, wherein the data processing unit is in the same state as when three-dimensional data obtained via the fan beam collimator rotating around the body axis is measured by a parallel collimator. A gamma camera characterized in that an image is reconstructed using a Fourier-Lebinning method for rearranging into two-dimensional multilayer data.