Simulations investigating the impact of depth-of-interaction in Nuclear Breast Imaging with a dedicated germanium gamma camera

With recent advancements in semiconductor contacts, electronics, and cryogenics, position-sensitive HighPurity Germanium (HPGe) cameras have become a feasible technology for biomedical applications, including Nuclear Breast Imaging (NBI). NBI with dedicated HPGe cameras could potentially become a suitable alternative to invasive biopsy when screening mammography yields inconclusive results, but improvements in sensitivity are desirable to reduce the activity needed and thereby reduce radiation dose. One method for improving sensitivity is to utilize a registered parallel-hole collimator with a wide acceptance angle. In this work, we use the Monte Carlo N-Particle (MCNP5) package to generate a simulated system matrix for a 1-cm-thick HPGe camera with a registered tungsten parallel-hole collimator that provides an 81 % increase in sensitivity compared to conventional parallel-hole collimation. Since HPGe is capable of providing depth-ofinteraction (DOT) information, the system matrix contains data for up to 10 discrete, I-mm-thick detector depths. When combined with the wide angular acceptance of the collimator, this DOT information can be used to perform limited-angle tomography using a single planar projection to compensate collimator blurring and improve contrast. Simulated data is used to investigate how employing DOT information in this limitedangle tomography scheme affects image quality compared to planar images.