SUBJECT: Ph.D. Dissertation Defense
BY: Linxi Shi
TIME: Friday, April 7, 2017, 1:00 p.m.
PLACE: Boggs, 3-47
TITLE: Quantitative Dedicated Cone Beam Breast CT imaging
COMMITTEE: Dr. Lei Zhu, Chair (NRE/MP)
Dr. C.-K. Chris Wang (NRE/MP)
Dr. Justin Roper (NRE/MP/EMORY)
Dr. Xiangyang Tang (BME/EMORY)
Dr. John N. Aarsvold (EMORY)


Recently, dedicated cone beam breast CT (CBBCT) has been approved by FDA to provide three-dimensional images for diagnostic breast imaging. Nevertheless, high scatter contamination stemming from large irradiation volume results in severe contrast lost and shading artifacts, impeding its quantitative uses in certain clinical tasks. Existing scatter correction methods demonstrate different drawbacks including low efficacy, dose or scan time increase, etc. In this work, we propose two scatter correction methods, library based and forward projection model based, to overcome the deficiencies while achieving high correction efficacy. In the library based method, a scatter library is precomputed via Monte Carlo simulation based on a simple breast model. Due to the relatively simple shape and composition, we find that a small library size with one input parameter of breast size is sufficient for effective scatter correction on general population. In the forward projection model based method, we first estimate primary signals of CBBCT projections via forward projection of the segmented first-pass reconstruction. By subtracting the simulated primary projection from the raw projection, we obtain a raw scatter estimate containing both low-frequency scatter and errors. After discarding untrusted errors from the resultant raw scatter map, the final scatter is obtained via a novel Fourier-Transform based local filtration algorithm. Both methods have demonstrated high correction efficacy on patient data, the library-based method is superior in computational efficiency while the forward projection model based method is more flexible. By comparing these two methods, we found that forward projection model based method tend to better preserve the high spatial resolution details than the library-based method. We hypothesize the existence of OFR is a fundamental factor degrading the image spatial resolution. To quantitatively investigate the effect of OFR on spatial resolution, we design an experiment to measure the spatial resolution w/ and w/o OFR. The obtained results successfully validate our hypothesis.