High performance SPECT camera design

Abstract

SPECT is primarily used in the clinic for cardiac applications like myocardial perfusion imaging (MPI). However, for SPECT, sensitivity is impaired due to the need for collimation. System resolution is poor as well (FWHM~1cm). New SPECT camera designs have emerged with improved sensitivity over the standard gamma cameras currently used in the clinic for estimating myocardial perfusion. Most of them focus on a region around the heart. The UFC design from GE or the multi-pinhole design by Funk et al use stationary pinholes configurations. The advantages of pin-hole designs are that there are no moving parts reducing long-term servicing costs. We propose a novel design to improve resolution and/or sensitivity over the flat-detector multi-pinhole designs by using curved detectors fitted to pin-holes. This will obtain improved resolution over that of a flat-detector attached to the same pin-hole due to increased magnification. We can then trade-off sensitivity versus resolution to get increased sensitivity for similar resolution as the flat-detector (by increasing the hole diameter). We derived expressions for average resolution for paraboloid, conical, and spherical detectors. We simulated the resolution and sensitivity improvement for examples cases for paraboloid, conical and spherical detectors for a stationary configuration of pinholes focused in a region in the object space, designed for cardiac application. For a paraboloid design, for cardiac SPECT application, the estimated sensitivity improvement over a multi-pin-hole system by Funk et al, was 48-85% for similar resolution. For a conical design, the improvement was 40-75%. The sensitivity improvement of the curved detector system over the clinical systems currently used in the clinic for cardiac imaging (using LEHR parallel collimation) was a factor of 7.4 to 9.3 for paraboloid (and 7 to 9 times for conical), with resolutions close to that of LEHR parallel collimation in the region of interest. Further there are tunable surface-parameters (such as height) if application calls for greater sensitivity and/or resolution, without changing the compactness (base-diameter) of the design. Finally, the performance of the paraboloid and conical design was better than the spherical design for this application, which suggests there may exist an optimum surface of the curved detector yielding the best improvement of resolution and/or sensitivity.