The development of MRI-compatible SPECT system

In recent years, combined MRI and nuclear imaging techniques such as PET and SPECT have received great attentions. MRI provides high-resolution anatomical and functional information along with an exquisite soft tissue contrast. Nuclear techniques could provide an excellent sensitivity to radio-labeled tracers that could be used to follow kinetic molecule interactions. In recent literatures, research on MRI/PET have been widely reported, but the development of combined MRI/SPECT is relatively limited, partially due to the stringent requirements on MRI-compatible SPECT detectors and the interferences between SPECT and MRI systems both operated at the same time. This dissertation proposed and developed a prototype of the MRI-compatible SPECT imaging system based on a recently developed energy-resolved photon counting (ERPC) CdTe detectors. These detectors consist of CdTe detectors of 1 mm or 2 mm thickness with 350µm pixels. The emphasis of this effort is to develop an ultrahigh resolution (sub-500µm) SPECT integrated with a clinical 3T MR scanner. The designed experimental studies have demonstrated the compatibility of the ERPC detectors for operation inside the 3T magnetic. Furthermore, to achieve high imaging performance, it is crucial to develop a precise model of the charge- collection behavior for CdTe detectors operated in strong magnetic field for reconstruction. In this study, a comprehensive Monte Carlo model has been developed for predicting the response function of the small-pixel CdTe detectors operated inside the MR scanner. This model includes all major physical processes, ranging from gamma ray interactions, charge generation and drifting under strong magnetic field. This model was subsequently validated in a comparative study against experimental results and imaging performance obtained with a prototype MRI-compatible SPECT system. Finally, the experimentally calibrated detector response model was successfully applied to improve the imaging performances of several MRI-compatible SPECT systems built with different detector configurations and MR scanners of different field-strengths. This study provided critical insights for further development of the MRI-compatible SPECT system for achieving an ultrahigh spatial resolution