Study Of PMT Cathode Uniformity Effect On PET’s Performance

PET/CT is a new medical imaging equipment, which integrated and fused two kinds of technologies of positron emission tomography(PET) and X-ray tomography(CT). PET is able to reflect the physiological and pathological situation of human body’s tissues and organs from the molecular level, and CT X-ray can detect the rays passing through the human body to obtain the amount of lesion location, integrating these two can achieve a higher image quality, it is quite significant and also has a very important role in earlier diagnosis for cancer.Detector is the main component of PET, most detectors are coupled of crystal and photomultiplier tubes(PMT). The detector captures the γ photons which are produced by positron annihilation, then PMT will convert the received photons into an electrical signal by its photoelectric conversion and signal amplification function, eventually present the disease situation of body on the image. Since those γ photons are all a pair of photons which have the same energy and the opposite directions, so as to capture these photons, PET detectors distribute by a ring shape, so there need a lot of PMTs.PMT is an important component of PET detector, so its performances are good or not will have a huge effect on the quality of image, in which PMT cathode uniformity is the most important factor to affect the resolution of detector. Therefore, in order to guarantee the image quality of PET, a test system was built up for testing the cathode uniformity of CR260 PMT which are used in PET. The system will screen the qualified tubes for PET, and it also provides a basis for studying the impact on PET from PMT cathode uniformity.The test system includes the light source, black box, scanning galvanometer, high voltage power supply and the software. Choosing LED for the light source of test system, using two diaphragms for limiting and straitening the light beam. Putting the source system and scanning galvanometer into the dark box to achieve effective dark. PC and MCU communicate each other by serial port, the LabVIEW program controls the both X-axis and Y-axis galvanometers to turn the light, and thus be able to complete the entire scanning of PMT.After setting up the test system, I tested the CR260 used in PET detector by this test system, and introduced the steps of the experiment, the method of achieving and processing data. Fitting the data by LabVIEW and MATLAB, getting the 2D and 3D images of PMT uniformity, and also a conclusion of PMT cathode no-uniformity. At the same time, comparing the good result and bad one, people can evaluate the cathode uniformity of PMT by comparison, and it also provides a basis for the study of the PMT cathode uniformity impact on PET.Verified by test, the test system I built up can actually improve the detection efficiency and accuracy of PMT, and improve the production efficiency, so it can present the very good practical effect.