Advanced Methods in Molecular Breast Imaging

Abstract

Molecular breast imaging (MBI) is a relatively new clinical breast imaging modality, which has the potential to have a significant impact in breast cancer screening and perioperative breast imaging for women with high risk factors for developing breast cancer. Two objectives were proposed in this thesis to increase the use of MBI. First, a magnetic resonance (MR)-compatible gamma camera was developed for combined molecular/MR breast imaging. MBI is a functional imaging technique with high specificity and sensitivity but could benefit from the addition of anatomical information from breast MRI for lesion localization, cancer staging, treatment planning and monitoring. A small area (8cm x 8cm) cadmium zinc telluride (CZT) based gamma camera was developed and tested for MR compatibility in both sequential and simultaneous imaging conditions. Results indicated that the gamma camera was minimally affected during both sequential and simultaneous imaging with a gradient echo (GRE) and spoiled gradient echo (GRE) sequence. Signal to noise ratio (SNR) degradation was observed in the MR images but no geometric distortions were observed. Simultaneous imaging is feasible, but a reassessment of the RF shielding would be required to minimize the noise contribution degrading image quality. Second, backscatter photons were investigated as a potential dose reduction technique for MBI. While the effective dose from MBI is relatively low in comparison to other nuclear medicine procedures, the dose is considered high in relation to mammography and in order to increase acceptance as an alternative breast imaging method, dose reduction is an important objective. Backscatter photons have the same spatial information as primary photons but are typically discarded along with other scattered photons. A scatter compensation method called the triple energy window (TEW) was used to extract backscatter photons from the Compton scattering spectrum and added to the primary photons, increasing count sensitivity by 6%. The noise level matched the increase in contrast leading to negligible change in lesion contrast to noise ratio (CNR). Dose reduction is not justified with this particular technique because of the elevated noise level, but the use of backcsatter photons show potential with improved contrast.