Development of a Cadmium Zinc Telluride Based Gamma Camera for Simultaneous SPECT/MR Imaging

Abstract

The current forefront of research in medical imaging technology includes working towards the combination of multiple imaging modalities into a single scan. SPECT is an imaging modality that would benefit from a combined approach with MRI allowing for improved diagnostic capabilities particularly in soft tissue regions. However, the traditional detectors used in SPECT are not capable of operating in the presence of an MRI magnetic field. This has led to the requirement for development of new gamma camera designs using modern solid state detectors. We have developed the hardware and software for a gamma camera design using cadmium zinc telluride detector technology. The camera will be used in a SPECT system being made up of multiple individual gamma camera modules. These modules will be placed in a ring that can be inserted into the MRI bore as a stationary insert for simultaneous SPECT/MR imaging. Testing of the mutual compatibility of the two systems has led to the development of a gradient triggering hardware and software protocol. Subsequent testing of this method in a clinical 3T MR was performed. When gradient triggering was enabled, erroneous event data from the mutual interference was reduced to near zero levels and resultant images show no structural differences when compared to control acquisitions. During gradient application, the CZT modules are suspended, thus yielding a 60% drop in sensitivity due to the additional deadtime of the triggering. The produced MR image showed a reduction in SNR of 92%. Co-registration of the MR and gamma camera images was successfully performed, showing both the physical structural and radioactive activity distribution of the phantom. Additionally, the potential of a diverging fan beam collimator for use in the multimodal SPECT/MR system was investigated using Monte Carlo simulations. Eleven collimator designs were compared, yielding between 13 to 23 modules per ring. The results showed that a practical SPECT/MR design using 18 detectors per ring with a 3.83 iii cm length collimator gave similar tomographic resolution to that of a clinical SPECT/CT system but with 7.0 times greater detection sensitivity compared to a conventional rotating dual-head camera. The simulations also showed that the system suffers from aliasing effects when reconstructing features of 7.9 mm or less. To further investigate how the design choices affected the tomographic resolution, parameters for collimator hole size, detector pixel size, and number of projection angles were also explored.