Date of Award
Spring 2012
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Biomedical Engineering
First Advisor
Gilat-Schmidt, Taly
Second Advisor
Stevens,Grant
Third Advisor
Olson, Lars
Abstract
This thesis aims to quantify the reduction in radiation dose deposited in glandular breast tissue achieved by using tilted gantry acquisition during cardiac CT scans. Previous work by Halpern et al. suggested using tilted acquisition parallel to the long axis of the patient’s heart. However, for a larger portion of the population this is not feasible due to the design of current scanners (which are limited to maximum tilt angles of 30 degrees). This study investigated the potential dose reduction and image quality effects at commercially available tilt angles between 0-30 degrees through simulation and experimental studies.
Upon IRB approval, datasets from 10 female patients from Froedtert Hospital (Milwaukee, WI) were used to create voxelized phantom models for the computer simulation. Experimental measurements were performed with an anthropomorphic phantom on a clinical CT scanner (Discovery CT750HD, GE Healthcare, Chalfont St. Gilates, England). For both simulation and experimental studies, radiation dose to the breast and reconstructed image signal-to-noise ratio (SNR) was quantified for tilt angles between 0-30 degrees in five degree increments.
The simulated and experimental results demonstrate that tilted gantry acquisition reduces the glandular breast dose from cardiac CT scans when compared to conventional (non-tilted) axial scans. Maximum reductions of 33%-81% (mean, 55%) were achieved with a 30-degree gantry tilt. However, a decrease in image quality by approximately 15% when compared to non-tilted images is seen in the simulated results. The image quality is found to remain equivalent, on average, up to a 15 degree tilt.