New radiation dose saving technologies for 256-slice cardiac computed tomography angiography

Purpose: This paper aims to evaluate the dose reductions conferred by spiral dynamic z-collimation and axial adaptive z-collimation for retrospectively and prospectively ECG-referenced cardiac CTA, respectively, on a wide coverage, 256-slice CT scanner. Methods: Using typical data presented in the literature, a distribution of cardiac CT scan lengths was synthesized. To isolate the effect of z-overscan on effective radiation dose, 1,000 simulated patient scan lengths were then randomly sampled from this distribution and used for subsequent analysis. Results: Retrospectively ECG-gated spiral scans with dynamic z-collimation resulted in a mean relative effective dose reduction of 11.7 and 24.3% for MDCT with 40 and 80 mm z-axis detector coverage, respectively. Mean relative dose reduction of prospectively ECG-triggered axial scans with adaptive z-collimation on an 80 mm coverage scanner was 10.0%. Conclusion: Dynamic z-collimation for retrospectively ECG-gated spiral scanning and adaptive z-collimation for prospectively ECG-triggered axial scanning are both associated with a significant dose reduction on a wide coverage, 256-slice CT scanner.