Short-Trajectory artifact-reversal diffusion for CCTA calcium deblooming

Background: Calcium blooming in coronary CT angiography (CCTA) enlarges calcified plaques, obscures the coronary lumen, and complicates stenosis assessment. Objective: To develop an efficient restoration method that suppresses blooming while preserving calcium and recovering adjacent lumen structure. Methods: We propose Short-Trajectory Artifact-Reversal (STAR) Diffusion, which progressively transforms a blooming-corrupted patch toward a debloomed target. Soft Annular Boundary Attention (SABA) reduces attention leakage from the blooming-prone annulus into the calcium core. Results: On 232 held-out synthetic 3D test cases, each sampled from a distinct anatomical location and unique plaque, background, calcium concentration, and exposure/noise configuration, STAR Diffusion achieved Dice 0.9248, Core RMSE 134.99 HU, and Annulus RMSE 90.05 HU. Metrics were computed after slice-wise inference and volumetric reassembly, with one matched case-level measurement per test volume for direct comparison across methods. The method improved calcium-region agreement and annular error relative to classical, GAN-based, and latent diffusion baselines, while ablations showed complementary contributions from spatial-prior conditioning and SABA. STAR Diffusion also reduced inference time compared with long-trajectory latent diffusion. Conclusions: In synthetic paired-data experiments, short-trajectory, spatially guided diffusion with boundary-aware attention reduced blooming while preserving plaque morphology and apparent lumen visibility. Clinical examples showed qualitatively similar behavior across plaque shapes and backgrounds.