Author: Ahad Ollah Ezzati, Xiaoyu Hu, Xun Jia, Youfang Lai, Kai Yang, Yuncheng Zhong 👨🔬
Affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Massachusetts General Hospital, Johns Hopkins University 🌍
Purpose: Gantry motion and patient breathing during a breast cone beam CT (bCBCT) scan is one of the major challenges for microcalcification (μCalcs) detection. By deploying a large number of individual x-ray sources and detectors around the breast, the bCBCT system can remain stationary. This study conducts Monte Carlo (MC) simulation to investigate feasibility and advantages in μCalc detection of the static photon-counting bCBCT.
Methods: We considered a stationary polygon shape bCBCT made from 51 CdTe photon counting detector panels with size of 2.5×40 cm2 and 306 carbon nanotube-based x-ray sources with 4 mm spacing and 0.1 mm focal spot size. The VICTRE toolkit was employed to generate a realistic breast phantom with (0.25mm)3 voxel size, 80% fat fraction and 14 cm diameter. μCalcs of spherical shapes with diameters from 0.1 to 0.4 mm were inserted. 306 projections were simulated with a total number of 5.9×1012 photons, corresponding to ~4 mGy mean glandular dose similar to a two-view mammography. The images were reconstructed with a modified filtered back projection algorithm to accommodate the polygon detector geometry. Image quality and calcification detection performance were evaluated.
Results: Contrast-to-noise ratio (CNR) of the μCalc ranged in 2.5-17.1 depending on their sizes and locations. Considering the CNR = 2.0 as the threshold for μCalc detection feasibility, the static photon-counting CT system can detect the μCalcs with 0.1 mm size. The total simulation and reconstruction time was approximately 2 days. The process was primarily dominated by the MC simulation, whose duration scales with the number of photons and inserted μCalcs.
Conclusion: Our MC simulation demonstrated the potential feasibly of the static photon-counting bCBCT for detecting μCalcs with 0.1 mm in diameter.