Development and Initial Evaluation of an MR Compatible Preclinical SPECT Insert for Simultaneous SPECT/MR Imaging
Rittenbach, Andrew Joseph
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Multi-modality medical imaging systems have become increasingly important in research and clinical applications of biomedical imaging. Two complementary imaging modalities that have not yet been fully integrated into a multimodality system are Single Photon Emission Computed Tomography (SPECT) and Magnetic Resonance Imaging (MRI). To this end, our team has developed an MR compatible SPECT insert for simultaneous preclinical SPECT/MR imaging. The SPECT insert’s detector is composed of five rings Cadmium Zinc Telluride (CZT) detector modules and an interchangeable cylindrical multi-pinhole (MPH) collimator. This dissertation discusses several new and significant contributions made towards the development of our SPECT insert. We developed methods to determine optimized design parameters for MPH collimators for the SPECT insert. These methods were used to design two MPH collimators with different imaging resolutions. Simulation results demonstrated that both collimators can be used to obtain artifact-free SPECT images with the designed resolutions. We then developed novel techniques to fabricate the collimators using MR compatible materials. Without proper system calibration and data correction, SPECT images reconstructed from data acquired with our insert exhibit poor image quality. We developed a novel energy calibration method to identify the photopeak of the gamma photons from a Tc-99m source at all 24,320 detector pixels simultaneously and a two-stage detector uniformity correction method to identify and correct for non-uniformities and malfunctioning pixels in the detector modules. Additionally, a method was developed to correct for the drift of electron-hole pairs within the detector modules due to the Lorentz force when operating the SPECT insert inside a magnetic field. After applying the system calibration and correction methods to the acquired data, reconstructed SPECT images showed significant improvement in terms of resolution, uniformity, contrast, and artifact reduction. Finally the SPECT insert was evaluated experimentally as a standalone SPECT system and as an insert inside an MRI system for simultaneous SPECT/MR imaging through phantom and small animal studies. The experimental results demonstrated that the SPECT insert met design specifications. Most importantly, results demonstrate that the insert can be used to obtain high quality SPECT images during simultaneous SPECT/MR image acquisition.