Molecular Breast Imaging Using Synthetic Projections From High-Purity Germanium Detectors: A Simulation Study

High-purity germanium (HPGe) gamma cameras are an emerging technology for molecular breast imaging (MBI) due to their 2-D lateral spatial resolution, depth-of-interaction (DOI) estimation, and superb energy resolution. In this simulation study, we investigate the potential imaging performance of an opposing view dual-head HPGe breast imaging system using a synthetic-projection technique, which utilizes DOI data with varying degrees of overlap in an ordered-subset estimation-maximization reconstruction algorithm to create 3-D images from which new 2-D projections are then created. The radiation transport simulator Monte Carlo N-particle was employed to generate projections from 10-mm thick HPGe detectors using tungsten parallel-hole collimators with short and wide holes. Simulations modeling 140-keV emissions from various contrast-detail and breast-torso phantoms were conducted. Synthetic projections were generated along with conjugatecounting images from collected HPGe projections. Tumor contrast, signal-to-noise ratio (SNR), and hot-spot detection measurements were used to compare images. Results show that the synthetic projections could resolve more low-contrast tumors compared to single-camera projections and conjugate-counting methods. MBI simulations also showed increased contrast and SNR in synthetic projections compared to individual projections. In conclusion, the HPGe imaging system employing a synthetic-projection technique may offer advantages over individual dual-camera projections or conjugate-counting methods in terms of contrast, SNR, and tumor detectability.