Development of a motorized variable angle slant-hole collimator

We developed a motorized variable angle slant-hole collimator (VASH) for a breast-specific gamma imaging detector. The collimator system consists of a stack of 48 tungsten sheets, four wedge blocks, and two motorized actuators for moving the wedge blocks. User controlled shearing of the stack of tungsten sheets can provide multiple projection angles allowing the implementation of limited angle tomography also known as tomosynthesis. Each individual sheet has an edge profile with a different angled cut on each side. Face matching wedge blocks, driven by two servo motors provide accurate positioning of each sheet resulting in the desired collimation angle. A prototype plastic model was built using a 3D printer to verify the design of the drive mechanism. The final product was built using 48 tungsten sheets with 0.255 mm thickness. The range of collimation angle is 29 degrees for each direction.