JPS6057553B2 - Coincidence detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coincidence detection device for detecting simultaneous occurrence of scintillation in two scintillators in a radiation computed tomography apparatus.

Radial computed tomography equipment takes RI (radioactive isotope) into the patient's body, and when RI accumulates in specific organs, it detects the radiation emitted from the RI outside the body and creates a distribution image of R1 on a specific tomographic plane. There are components.

When a positron radionuclide is used as a radionuclide, two gamma rays are generated in the 1800 direction, so if these gamma rays are incident on opposing scintillators and it is detected that scintillation occurs simultaneously, the gamma rays can be detected. You can know the location of the generation point. Conventionally, in order to detect this coincidence, the light from the scintillator was immediately converted into an electrical signal and processed on an electrical circuit.

However, since the time span of scintillation light is extremely short, it is inevitable that some degree of coincidence loss will occur due to effects such as temperature drift and variations in circuit elements. The object of the present invention is to obtain a coincidence detection device that solves the above problems by improving the optical signal in stages.

An embodiment of the present invention will be described below with reference to the drawings.

In Figure 1, 2
scintillators 1 and 2 are arranged facing each other, and two optical fibers 3 and 4 are connected between the scintillators 1 and 2 and the entrance surface of the Kester prism 5, respectively.
The optical lengths of these two optical fibers 3 and 4 are made equal. The interference output light from the Kester prism 5 is guided to a photomultiplier tube 6, converted into an electrical signal, and then sent to a discriminator 8 via an amplifier 7. Now, suppose that the positron of the RI of the positron radionuclide is annihilated at point 9, and two γ-rays are emitted in the 1800 direction. Then these two γ
The line simultaneously irradiates two scintillators 1 and 2 that are arranged opposite each other, causing scintillation at the same time. Since this scintillation light has a single wavelength and the optical lengths of the optical fibers 3 and 4 are equal, both scintillation lights enter the entrance surface of the Kester prism 5 at right angles at the same timing and phase. The light emitted from both persons enters the central harmor mirror 51 after being aimed. Here, since the light beams emitted from both persons are in the same phase, they interfere at the half mirror 51, and the intensity of the interference output light is doubled. That is, FIG. 2A shows the intensity of light guided by the optical fiber 3, FIG. 2B shows the intensity of the light guided by the optical fiber 4, and FIG. 2C shows the interference output light. In the case of the same phase, the intensity of the interference output light is doubled as shown by the hatched area. On the other hand, scintillation light that is not generated by simultaneous human emission of γ-rays does not have the same phase, so the intensity of the interference output light is not doubled. The level of the electrical signal (output signal of the amplifier 7) of this interference output light is as shown in FIG. 2D, so the upper level UL and lower level LL of the detection window of the discriminator 8 are By setting as shown in FIG. 2D, level selection becomes possible, and a signal for detecting the simultaneous occurrence of scintillation can be outputted from the discriminator 8 as shown in FIG. 2E.

As explained above in the embodiments, according to the present invention, coincidence is basically determined not at the electrical signal stage but at the optical signal stage, so detection errors caused by instability in the electrical circuit, etc. No detection loss occurs.

Furthermore, since 100% of the light from the scintillator is used and absolute measurement is performed optically, the detection efficiency is improved. And its configuration is extremely simple.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a time chart for explaining the operation. 1, 2... - scintillator, 3, 4... optical fiber, 5... Kester prism, 6... photomultiplier tube,
7... Multiplier, 8... Discriminator, 9...
- Location of RI.

Claims (1)

[Claims] 1. It has two light guides that guide light in the same phase from two opposing scintillators, and a Kester prism into which the light from the output end of each light guide is incident. Both incident lights are passed through the half mirror of the Kester prism. A coincidence detection device that selects a level by photoelectrically converting the interference output light.