We have developed a compact and mobile gamma imaging system that is designed for both PET and SPECT acquisitions within a bedside environment, such as an intensive care unit, surgical suite, or emergency room. This paper describes the SPECT performance evaluation of the system for cardiac imaging, including both Tc-99m and F-18 radionuclides. For cardiac F-18 imaging in a bedside environment, the 511 keV SPECT approach using high energy collimation and anterior 180 degree acquisition has the advantages of not requiring a detector to be positioned beneath the bed and greatly reducing attenuation effects. In this study, we evaluated SPECT reconstructed image quality using an anthropomorphic dynamic cardiac phantom filled with Tc-99m and F-18 separately. The specific issues that were addressed in this study included the following: 1) mitigating septal penetration effects with the 511 keV photons using de-convolution filtering, 2) reducing truncation effects due to the relatively small field-of-view of the camera using angle-dependent center-of-rotation shifts, and 3) investigating the effects of reduced angular sampling and angular range. We found that reducing angular sampling to 28 projections through 135 degrees with Tc-99m and 25 projections through 180 degrees with F-18 showed all features of the myocardium.

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Purpose: The objective of this study is to evaluate the imaging performance of a mobile SPECT system with a pinhole collimator and compare the results with parallel hole collimators. The goal is to obtain both planar and tomographic performance measures with Tc‐99m and F‐18. This abstract presents the results using Tc‐99m. Method and Materials: The system utilizes a small field of view camera with pixilated NaI crystal and position‐sensitive photomultiplier tubes. The pinhole collimator is a tungsten knife edge with a hole diameter of 3mm, a focal length of 12.5cm, and an acceptance angle of 90 degrees. The parallel hole collimators have been previously described along with their imaging performance evaluation [1]. The following performance measures with the pinhole collimator were obtained and are presented here: count rate performance, energy resolution, flood field uniformity, system spatial resolution, system sensitivity. Results: The maximum count rate was calculated to be 1.58×105 cps corresponding to an activity of 161 μCi at 30cm. An energy spectrum from the flood acquisition demonstrated an energy resolution of 20% FWHM. Magnification corrected, system planar spatial resolution was 1.03 cm with a system sensitivity of 1.39 cps/μCi at a source to collimator distance of 10 cm. Conclusion: The imaging performance of a mobile SPECT system with a pinhole collimator has been presented. In comparison to parallel hole collimation, the pinhole collimator provides superior spatial resolution and sensitivity at distances less than 5cm. However, at further distances, pinhole sensitivity declines while parallel hole sensitivity remains relatively constant. Research sponsored by the United States Army Medical Research and Material Command under Award No. W81XWH‐04‐1‐0594

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