Towards quantification of dedicated breast SPECT using non-traditional acquisition trajectories

Quantification of radiotracer uptake in lesions can provide valuable information to physicians in deciding patient care or determining treatment efficacy. Physical processes (e.g. scatter, attenuation), detector/collimator characteristics, sampling and acquisition trajectories, and reconstruction artifacts contribute to an incorrect absolute measurement of tracer activity and distribution. For these experiments, a cylinder with three syringes of varying radioactivity concentration, and a fillable 800 mL breast with two lesion phantoms containing aqueous 99m Tc pertechnetate were imaged using the SPECT subsystem of the dual-modality SPECT-CT dedicated breast scanner. SPECT images were collected using a compact CZT camera with various 3D acquisitions including vertical axis of rotation, 30° tilted, and complex sinusoidal trajectories. Quantitative differences in the measured absolute activity values were investigated for each acquisition trajectory to determine the efficacy of an acquisition trajectory to quantify regions of focal uptake. With attenuation and scatter corrections applied, reconstruction image results showed that the measured average activity concentrations in the hot-spot areas corresponded to within 15% of the actual dose calibrator measured activity concentration. More complete sampling trajectories outperform incomplete tilted acquisition trajectories.