Radiation Dose Reduction and Image Quality Evaluation of Coronal Truncated Projections in Cone-Beam Dedicated Breast CT
S Konate1, S Vedantham2*, L Shi2, A Karellas2, (1) College of the Holy Cross, Worcester, MA, (2) University of Massachusetts Medical School, Worcester, MASU-E-I-1 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To investigate the radiation dose reduction and the effect of weighting schemes on image quality in cone-beam dedicated breast CT acquired with coronal truncated projections that is similar in concept as extended field-of-view imaging with laterally-shifted flat-panel detectors.
Methods: Three pre-weighting schemes were implemented in conjunction with filtered backprojection (FBP) reconstruction to study the effect of coronal truncation in dedicated breast CT. If the fan-angle of the non-truncated projections is represented as 2f (24-degrees), then coronal truncations corresponding to f+0.25, f+1.5, and f+2.7-degrees were investigated. Monte Carlo simulations using the GEANT4 toolkit were used to determine the radiation dose reduction at the aforementioned truncations. Projection images of a numerical phantom with dimensions representative of an average pendant breast containing six spherical signal objects in a homogenous background were reconstructed without and with truncation. Cone-beam projections from a diagnostic dedicated breast CT exam acquired with fan-angle of 2f were truncated at the aforementioned fan-angles and reconstructed. Phantom and clinical images were analyzed for artifacts and the visibility of signal features.
Results: For an average 14-cm diameter, 15% fibroglandular breast, the estimated dose reduction at fan-angles of f+0.25, f+1.5, and f+2.7-degrees were 47%, 34% and 21%, respectively. The severity of artifacts increased with decreasing fan-angle. The choice of weighting scheme does not appear to have a substantial effect on mitigating artifacts. At fan-angles of f+1.5 and above, shading artifacts were subtle and could not be easily discerned. The signal objects in the phantom and the microcalcification in the clinical images were discernible. For 10, 14 and 18 cm diameter, 15% fibroglandular breasts, the radiation dose reduction at fan-angle of f+1.5-degrees were 27%, 34% and 37%, respectively.
Conclusion: There exists a potential to reduce radiation dose by approximately 30% from cone-beam dedicated breast CT acquired with coronal truncated projections.
Funding Support, Disclosures, and Conflict of Interest: Supported in part by the National Institutes of Health (NIH) grants R01 CA128906 and R21 CA134128. The contents are solely the responsibility of the authors and do not represent the official views of the NIH or the NCI.