Development of an MRI-compatible cooling unit for SPECT/MRI detection modules

A new multi-modality imaging tool is under development in the framework of the INSERT (Integrated SPECT/MRI for Enhanced Stratification in Radio-chemo Therapy) project, supported by the European Community. The final goal is to develop a custom SPECT apparatus that can be used as an insert for commercially available MRI systems. INSERT is expected to offer more effective and earlier diagnosis with potentially better outcome in survival for the treatment of brain tumors, primarily glioma. Two SPECT prototypes are being developed, one dedicated to preclinical imaging (7 and 9.4 T), the second one dedicated to clinical imaging (3 T). The fundamental unit is a 5 cm × 5 cm gamma camera, based on the well-established Anger architecture with a continuous CsI:Tl scintillator readout by an array of silicon photomultipliers (SiPMs). In order to improve the noise performance of the overall SPECT system, the SiPM arrays need to operate at temperatures around 0 °C to reduce their Dark Count Rate (DCR). Thereby, the detection modules require mild to moderate cooling essential to achieve the final goals of energy and spatial resolutions. However, the presence of static magnetic field B
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, rapidly switching gradients and radio-frequency pulses in the bore of the MRI machine, make use of traditional cooling blocks with bulky metallic components unsuitable. In this work we describe the study of a MRI-compatible cooling unit, thermal simulations of their expected performance and the results of a test prototype.