The Temperature Compensation System Research And Design Of PET Detector

PET is a kind of using radioactive nuclide labeled molecule interactions in vivo molecular imaging techniques,in the field of modern medical imaging,gradually becomes the most advanced imaging techniques.Photoelectric detector is a device used to detect photon,which is the core of PET imaging system,photon fall into the scintillation crystals and take place positron annihilation,loss energy of incident particles during the process is converted into electrical signal by photoelectric detector,other parts of the imaging system filtering and amplification of signal processing,eventually get the positron annihilation of energy,time and other information.As a semiconductor device composed of avalanche diode,SiPM detector is sensitive to temperature and bias.SiPM detector gain is proportional to difference of bias and reverse breakdown voltage,the reverse breakdown voltage is under the influence of temperature,the temperature drift can lead to the change of the reverse breakdown voltage,and then make the probe gain change.Experimental results indicate that temperature change has a reverse breakdown voltage 28 mv / ? temperature coefficient,mean temperature changed 10 ?,the reverse breakdown voltage change about 0.28 V,compared with a few volts overvoltage,this is a great distortion.Temperature characteristic of photoelectric detector will not only affect the detector of other physical properties such as time resolution,and is the precondition of consistency computer reconstruction of PET images experiment conditions.So temperature compensation system became one of the focus in the study of PET at home and abroad,foreign scholars lines as early as 2000,the temperature characteristic of the SiPM research in recent years,a lot of SiPM temperature compensation system have been proposed.Through the survey found,on the one hand,a lot of temperature compensation scheme from abroad,domestic few relevant case study;On the other hand,many schemes have been not to meet the needs of the current application of PET,so this paper puts forward a kind of applied to the automatic temperature compensation of SiPM system.Based on the photoelectric detector is proportional to the gain of the SiPM in reverse bias voltage and reverse breakdown voltage of the principle of difference,put forward a kind of reverse biased by dynamically adjusting detector gain changes caused by high voltage to compensate for temperature changes.At home and abroad in this paper,several classic detector temperature compensation,this thesis probes into the system or application based on occasion to discuss their respective research innovations and shortcomings,its innovation points as the theoretical basis for the system design,but also has some shortcomings,such as have not been able to add detail to the temperature compensation system controller,cannot achieve the function of automatic temperature compensation.Or only applies to integration of MPPC photoelectric conversion module,system miniaturization but expensive.Its shortcomings will serve as the breakthrough point of system design,in the existing research results on deeper or comprehensive research.Based on the electronics design of each function module,temperature compensation system realizes the detector temperature measurement,to calculate the compensation current reverse bias voltage,temperature control detector output voltage of high voltage power supply module,PC real-time display the current detector temperature function,software design,using a high-level language C,respectively,developed a master control program,temperature acquisition,high voltage control program and serial communication;SiPM photoelectric device was designed using the Matlab language peak position calculating program;Design the system function verification and the final part is used to verify the effectiveness and practicability of the system.The SiPM detector gain characteristic test system is designed to build,draw a detector gain and temperature respectively,the relationship between gain and reverse biased voltage model,the relational model will be used as the basis for temperature compensation.In order to show the effectiveness and superiority of the function of this system,designed the two kinds of experiments,the first is a discontinuous collection and verification,the experiment result shows that not join removing system,in the case of 5 ? temperature change produces a 41.8% gain,after joining removing system,the change range was reduced to 3%.In the condition of 10 ? temperature change,gain change rate is 96%,then add the rate of 7.8% after removing system.The second continuous acquisition as a way of authentication,the experimental results show that because of the influence of temperature drift,gain change,energy spectrum diagram of photoelectric displacement peak position,makes the final cumulative distortion energy distribution curve and photoelectric displacement of 9.3% of the peak position.After joining temperature compensation system,the experimental results show that the change of the gain is offset,cumulative energy distribution curve compared with standard curve,almost no distortion,photoelectric peak position displacement amplitude of 0.47%.The results of the two kinds of acquisition powerful illustrates the temperature compensation system on the temperature drift compensation effect,achieve the design of the system,to realize the function of the system.In this paper,the research content including PET imaging system principle,the physical properties of SiPM detector,realization of each function module design system and the comprehensive function verification,the research and design is a complete,for the subsequent research has important reference value.