Abstract 251: Radiation Dose From Single Heartbeat Coronary CT Angiography Performed Using a 320 Detector-Row Volume Scanner
Introduction: Volume scanning (VS) offers the ability to perform coronary CT angiography (CCTA) in a fraction of a heartbeat. While VS decreases x-ray exposure time, which decreases radiation dose, it has also been suggested that it is associated with increased scattered radiation and overbeaming, factors that can increase dose.
Hypothesis: Radiation dose from CCTA is significantly lower using VS than using helical modes on the same scanner, while image noise is unchanged.
Methods: Radiation doses from CCTA using a volume scanner were determined using metal-oxide-semiconductor field-effect transistor detectors positioned in an anthropomorphic phantom physically and radiographically simulating a male or female human. Organ and effective doses were determined for 6 scan modes, including both 64-row helical and 280-row volume scans (Table⇓). Effective doses were compared to estimates based on the method most commonly used in clinical literature: European guidelines which multiply dose-length product (DLP) by a general conversion coefficient (0.017 or 0.014 mSv/(mGy*cm)), determined from Monte Carlo simulations of chest CT using single-slice scanners and previous tissue weighting factors.
Results: Effective dose was reduced by up to 88% in VS relative to helical scanning, with similar image noise. Effective dose, determined using current (ICRP Publication 103) methodology, was 7.8 mSv using VS with exposure permitting a wide reconstruction window, 5.5 mSv with optimized exposure, and 4.2 mSv for optimized 100 kVp scanning. Estimating effective dose using a chest conversion coefficient resulted in dose as low as 1.8 mSv, substantially underestimating effective dose for both VS and helical CCTA.
Conclusions: VS markedly decreases CCTA radiation doses compared to helical scanning. When conversion coefficients are used to estimate effective dose from DLP, they should be appropriate for the scanner and scan mode used and reflect current tissue weighting factors.