Dose reduction for coronary calcium scoring with hybrid and model-based iterative reconstruction: an ex vivo study

Purpose To determine the influence of dose reduction on coronary calcium scoring using hybrid and model-based iterative reconstruction (IR) techniques. Methods Fifteen ex vivo hearts were scanned in a phantom representing an average adult person at routine dose and three levels of dose reduction; 27, 55 and 82 % reduced-dose, respectively. All images were reconstructed using filtered back-projection (FBP), hybrid IR (iDose(4), levels 1, 4 and 7) as well as model-based IR iterative model reconstruction (IMR, levels 1, 2 and 3). Agatston, mass and volume scores found with iDose(4) and IMR were compared to FBP reconstruction (routine dose) as well as objective image quality. Results With FBP calcium scores remained unchanged at 82 % reduced dose. With IR Agatston scores differed significantly at routine dose, using IMR level 3 and iDose(4) level 7, and at 82 % reduced dose, using IMR levels 1-3 and iDose(4) level 7. The maximum median difference was 5.3 %. Mass remained unchanged at reduced dose levels while volume was significantly lower at 82 % reduced dose with IMR (maximum median difference 5.0 %). Objective image quality improved with IR, at 82 % reduced dose the CNR of iDose(4) level 7 was similar to the reference dose CNR, and IMR levels 1-3 resulted in an even higher CNR. Conclusion Calcium scores were not affected by radiation-dose reduction with FBP and low levels of hybrid IR. Objective image quality increased significantly using hybrid and model-based IR. Therefore low level hybrid IR has the potential to reduce radiation-dose of coronary calcium scoring with up to 82 %.