Simulating low-dose cone-beam CT: A phantom study

Our institution routinely uses limited-angle cone-beam CT (CBCT) from a C-arm with 3D capabilities to diagnose and treat cardiovascular and orthopedic diseases in both adult and pediatric patients. While CBCT contributes to qualitative and quantitative assessment of both normal and abnormal patient anatomy, it also contributes substantially to patient radiation dose. Reducing the dose associated with CBCT exams while maintaining clinical utility can be considered to be of benefit to patients for whom CBCT is routinely used and may extend its adoption to clinical tasks and patient populations where the dose is currently considered prohibitive. In this work we developed and validated a method to simulate low-dose CBCT images from standard-dose projection images. The method was based on adding random noise to real projection images. The method was validated using an anthropomorphic thorax phantom of variable size with a custom-made insert containing iodine contrast rods of variable concentration. Images reconstructed from the low-dose simulations were compared to the actually acquired lower-dose images. Subtraction images of the simulated and acquired lower-dose images demonstrated a lack of residual structure patterns, indicating that differences between the image sets were consistent with random noise only. Noise power spectrum (NPS) and iodine signal-difference-to-noise ratio (SDNR) showed good agreement between simulated and acquired lower-dose images for dose levels between 70% and 30% of the routine dose. The average difference in iodine SDNR between simulated and acquired low-dose images was below 5% for all dose levels and phantom sizes. This work demonstrates the feasibility of accurately simulating low-dose CBCT based on real images acquired using standard dose and degrading the images by adding noise.