Design of a dual-head multi-pinhole collimator for brain SPECT with improved axial sampling

Objectives: We designed a multi-pinhole (MPH) collimator for clinical brain SPECT imaging, which could potentially be used with the recently reported Tau-SPECT tracers (H. Watanabe et al, 2016). In this design two identical MPH collimators replace the existing collimators on a general-purpose-dual-head SPECT system. The pinholes are arranged at different axial positions to improve sampling. In addition, the collimator on one head is rotated 180 degree (about the axis normal to the collimator plane) with respect to the other one to further increase the axial sampling. Method: We determined the geometry of the system (e.g., number of pinholes, aperture size, aperture positions, aperture-center-of-field-of view distance, and aperture-detector distance) by maximizing system sensitivity for a target ellipsoidal (principal semi-axes, a:10.5, b:10.5, c:9 cm) volume-of-interest (VOI) covering 99-percentile head size and a target system resolution of 7 mm at the focal point on the axis-of-rotation. Constraints in optimization were fitting around the 99-percentile shoulder width of patients during rotation, minimum radius of rotation for brain, and