Molecular Imaging of the Breast Using a Variable-Angle Slant-Hole Collimator

Purpose: The purpose of this work is to develop an improved method for 3D molecular imaging of the breast using limited angle SPECT. Methods: The proposed method uses a variable-angle slant-hole (VASH) collimator. Rather than rotate the camera around the breast, the VASH collimator allows limited angle, tomographic acquisition while the detector remains stationary and flush against the compression paddle. This design minimizes object-to-detector distance for high spatial resolution. Theoretical analysis is presented of VASH spatial resolution and sensitivity, including depth-of-interaction (DOI) effects and magnification. The theory is compared with Monte Carlo simulation results for a point source and breast phantom including a compression paddle. An iterative reconstruction method for the slant hole data is used. Results: The theoretical model of the VASH system showed good agreement with Monte Carlo simulations based on spatial resolution, including DOI effects, and sensitivity. For 140 keV photons and a NaI(Tl) scintillator, the DOI effect resulted in roughly a 2 mm loss in spatial resolution only in depth dimension; in the other two dimensions the spatial resolution was not affected by DOI. In reconstructed breast phantom images, VASH out-performed a parallel hole SPECT approach in terms of contrast-to-noise ratio. Conclusions: The proposed method for breast imaging using limited angle SPECT and a VASH collimator demonstrated the potential for superior spatial resolution/sensitivity. In addition to high spatial resolution/sensitivity, the system design has advantages of simple detector motion, ability to image close to the chest wall and conducive to on-board biopsy and multi-modal imaging with mammography.