Abstract
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Objectives: The choice of collimation in SPECT imaging has typically been viewed as a critical decision for proper optimization of the system’s efficiency for a given imaging resolution. Although parallel-beam collimation is the most commonly used, viable alternatives include fan-beam, cone-beam - including spatially varying focal spots for each - slit-slat, and pinhole. Other considerations include the field of view (FOV) and sampling properties. The use of solid-state detectors with very high intrinsic spatial resolution may provide a pathway to very high resolution systems without a substantial loss in overall efficiency. In addition, these devices could allow flexibility in acquisition options for each patient.
Methods: The overall system efficiency was determined for pinhole and slit-slat geometries based on apertures at a distance of 16 cm from the center of a 16 cm FOV (heart-sized with some margin). The overall transverse detector sizes considered were integer multiples of 2 cm, based on prototype detector module at the University of Illinois. In this study, we kept a generic modular detector design, where each detector is 2 cm x 2 cm x 5 mm (thickness). The detector could have either 250-micron (80 x 80) pixels or 500-micron (40 x 40) pixels, and a DOI resolution of 0.5 mm. These design specifications could easily be achieved with existing CZT detector technologies. Various acquisition geometries were considered, including the detector seeing the entire FOV or a portion of the FOV with neighboring modules seeing adjacent and slightly overlapping regions of the FOV to fully cover the object. Resolution for all configurations was matched in the axial and transverse directions by adjusting the collimator parameters. Overall efficiency was calculated by averaging over the FOV.
Results: For large values of system resolution (10-15 mm), total sensitivity varies slowly with detector intrinsic resolution. For higher resolutions (5-8 mm), reasonable efficiency values of (2-4) x 10-5 can be achieved.
Conclusion: An evaluation of cardiac imaging with solid state detectors having high intrinsic spatial indicates much better volumetric resolution (27-64x finer) than typically achieve clinically may be possible with a modest loss in efficiency. The flexibility of these compact designs may further allow patient-specific optimizations that enable large additional factors in efficiency recovery by enabling imaging close to the patient through mosaic imaging of the FOV. In conclusion, geometrical design of cardiac SPECT with small detector modules allows flexible imaging and the capability of very high spatial resolution. Research Support: This work was supported by the National Heart, Lung, and Blood Institute (NHLBI) and the National Institute for Biomedical Imaging and Bioengineering (NIBIB) of the National Institutes of Health under grants R01HL108119 and R21EB021559, respectively.