Simulation of calcium blooming artifacts in coronary CT angiography from digital phantoms

Background: Calcium blooming artifacts, predominantly caused by the partial volume effect, may limit the accuracy of coronary stenosis assessment on coronary computed tomography angiography (CTA). Existing comparative tests or physical phantoms to evaluate de-blooming methods are costly, time-consuming, and limited in geometry and materials. This study developed a computational method to simulate CTA images incorporating calcified plaques from digital phantoms to help understand the characteristics of blooming artifacts.

Methods: Digital vascular phantoms with different plaque geometries and stenosis severities were created and imaged by computed tomography (CT) simulation. To assess the accuracy of simulation, CT images of three-dimensional (3D)-printed physical phantoms were acquired by CT scanners. To investigate the consistency of the impacts of tube voltage and reconstruction kernel on calcium blooming artifacts, both simulated and acquired CT images were quantitatively analyzed.

Results: The average structural similarity index measure (SSIM) of simulated and acquired images was 0.94±0.04. CT number, image noise and calcified area comparison between the simulated and corresponding acquired images showed good agreement. Normalized calcified area was 1.12±0.13, 1.05±0.12, 0.99±0.11 (P<0.001), for 80, 100 and 120 kV, respectively, across the simulated and acquired images. Normalized calcified area was 0.93±0.04, 0.96±0.06, 1.02±0.05, and 1.07±0.16, for reconstruction kernels from sharp to soft (P<0.001) for simulated images; result was 0.99±0.17 (sharp) vs. 1.09±0.13 (soft) for acquired images (P<0.001). Linear regression analysis indicated that measured calcified area increased as tube voltage decreased or reconstruction kernel became softer (r²>0.98) both for simulated and acquired images.

Conclusions: Simulated CT images from digital phantoms resembled the acquired images by CT scanners. Tube voltages and reconstruction kernels significantly affected the extent of calcium blooming artifacts both for simulated and acquired images. The proposed framework for calcium blooming artifacts may provide an in silico testbed for improving coronary CTA interpretation.