Step-and-shoot versus continuous helical pinhole SPECT for improved axial resolution

Abstract

Pinhole SPECT provides high-resolution, high-sensitivity images of small animals and small human organs like the thyroid. Helical-orbit scans with continuous linear-stage motion and step-and-shoot camera motion have been used to provide complete sampling and improve the axial resolution compared to circular orbit scans. In step-and-shoot motion (SSM), the camera rotates by predefined steps; between the steps the stationary camera acquires projection data for a given scan time. The linear stage continues to move even when the camera is stepping. This may result in the loss of axial resolution. Experimental and simulation studies were performed. Combinations of SSM and continuous motion (CM) of the linear stage with SSM of the camera were compared for various number of views using 360 deg. circular orbit The axial resolution of the reconstructed images was evaluated for comparison. The difference in axial resolution achieved using CM and SSM of the linear stage is similar for experimental data. At the current axial resolution that has been achieved, SSM and CM acquisition yield similar resolutions. Independent improvements in axial resolution may show differences in axial resolution for the two acquisition methods. Using a 60-view scan might yield similar results to a 180-view scan at a reduced total acquisition time.