A prototype gamma tomosynthesis system for molecular breast imaging

We are developing an improved gamma camera for molecular breast imaging (MBI) that allows tomographic imaging and improved signal-to-noise over conventional planar methods. We have built a novel gamma camera for MBI that utilizes limited angle tomography, similar to x-ray tomosynthesis, to generate images with depth information and improved signal-to-noise. A unique feature of the gamma tomosynthesis system is a variable-angle slant hole (VASH) collimator. This collimator allows the camera to remain flush against the compression paddle during the tomographic acquisition, which achieves high spatial resolution and simplified detector motion. We constructed a VASH collimator from a stack of tungsten sheets, each sheet containing a matrix of holes created by photo-etching. With the holes of the sheets aligned, a parallel-hole collimator is created; shearing the sheets creates a variable angle slant hole collimator. The shearing is controlled by a motorized mechanism. The collimator was mounted on a commercial MBI camera and projection data were acquired of a set of capillary tube line sources over a 50° range of angles. The projection data were reconstructed using the iterative MLEM method. Results demonstrated the ability of the system to resolve in the depth dimension, and spatial resolution matched expected values. We conclude that the proposed gamma tomosynthesis system has the potential to provide improved signal-to-noise over conventional MBI methods and allow a reduction in the administered radioactivity and patient dose.