Performance characteristics of the inSPira HD, a new generation brain-dedicated SPECT camera

Objectives We have conducted resolution testing on the inSPira HD camera (Neurologica, Inc.), a new generation brain-dedicated SPECT camera, using 72 NaI detectors with focused collimators on a circularly rotating gantry allowing for a variable radius of the detectors relative to the system isocenter. This performance testing compares I123 imaging using the InSPira to a conventional 3-headed camera with fan beam collimators; quantitative measures document contrast recovery in small structures as would be important in studying Parkinsons disease.

Methods A phantom (inside diameter = 14cm) with cold rod inserts was filled with water and 1480 MBq I123. Fillable spheres contained activity 4 times that of the background. The phantom was imaged for 5 days on both the inSPira, with slice thickness of 4 or 8mm as well as on a Picker Prism SPECT camera with slice thicknesses of 3.56mm. Adjacent Prism slices were summed to approximate 8mm resolution. Both hot and cold contrast recoveries were evaluated.

Results For early time points, 5 of the 6 sizes of cold rods were visible on the InSPira. Only 2 sections were visible when scanned on the Picker. The cold rod contrast ratio (ideally = 0%) was measured as 52-83% for the visible sections on the inSPira, compared to 56 and 63% for the visible sections on the Prism. Similarly, when evaluating the hot sphere contrasts (ideally = 4.0), the inSPira measured 2.83-1.53 for the visible spheres, compared to 1.93-1.32 for the visible Prism spheres. At time points >50 hours post injection, cold rod resolution on the InSPira degraded by ~10%.

Conclusions Since the spatial resolution of the inSPira (3mm) is higher than the Prism's (6mm), the InSPira camera has improved cold rod and hot sphere contrast recovery. As expected, these high activity values degrade for both cameras at lower activity levels, and the hot and cold resolutions were always better at 4mm than 8mm reconstruction resolutions