Estimated radiation dose associated with cardiac CT angiography.

CONTEXT: Cardiac computed tomography (CT) angiography (CCTA) has emerged as a useful diagnostic imaging modality in the assessment of coronary artery disease. However, the potential risks due to exposure to ionizing radiation associated with CCTA have raised concerns. OBJECTIVES: To estimate the radiation dose of CCTA in routine clinical practice as well as the association of currently available strategies with dose reduction and to identify the independent factors contributing to radiation dose. DESIGN, SETTING, AND PATIENTS: A cross-sectional, international, multicenter, observational study (50 study sites: 21 university hospitals and 29 community hospitals) of estimated radiation dose in 1965 patients undergoing CCTA between February and December 2007. Linear regression analysis was used to identify independent predictors associated with dose. MAIN OUTCOME MEASURE: Dose-length product (DLP) of CCTA. RESULTS: The median DLP of 1965 CCTA examinations performed at 50 study sites was 885 mGy x cm (interquartile range, 568-1259 mGy x cm), which corresponds to an estimated radiation dose of 12 mSv (or 1.2 x the dose of an abdominal CT study or 600 chest x-rays). A high variability in DLP was observed between study sites (range of median DLPs per site, 331-2146 mGy x cm). Independent factors associated with radiation dose were patient weight (relative effect on DLP, 5%; 95% confidence interval [CI], 4%-6%), absence of stable sinus rhythm (10%; 95% CI, 2%-19%), scan length (5%; 95% CI, 4%-6%), electrocardiographically controlled tube current modulation (-25%; 95% CI, -23% to -28%; applied in 73% of patients), 100-kV tube voltage (-46%; 95% CI, -42% to -51%; applied in 5% of patients), sequential scanning (-78%; 95% CI, -77% to -79%; applied in 6% of patients), experience in cardiac CT (-1%; 95% CI, -1% to 0%), number of CCTAs per month (0%; 95% CI, 0%-1%), and type of 64-slice CT system (for highest vs lowest dose system, 97%; 95% CI, 88%-106%). Algorithms for dose reduction were not associated with deteriorated diagnostic image quality in this observational study. CONCLUSIONS: Median doses of CCTA differ significantly between study sites and CT systems. Effective strategies to reduce radiation dose are available but some strategies are not frequently used. The comparable diagnostic image quality may support an increased use of dose-saving strategies in adequately selected patients.

Reduction of radiation dose estimates in cardiac 64-slice CT angiography in patients after coronary artery bypass graft surgery.

OBJECTIVES: The objectives of this prospective investigation in patients after bypass graft surgery were (1) to estimate radiation dose for routine bypass graft computed tomography (CT) angiography, (2) to study the impact of anatomically adapted and ECG-controlled tube current modulation on radiation dose estimates, and (3) effects on qualitative and quantitative image quality parameters. METHODS: Radiation dose was estimated for 194 consecutive patients undergoing 64-slice CT angiography (Somatom Sensation 64 Cardiac, Siemens Medical Solutions). The impact of anatomically adapted tube current modulation was studied in 2 consecutive patients groups. Furthermore, the impact of ECG-controlled tube current modulation, applied as indicated, was evaluated in both groups. RESULTS: Mean radiation dose estimate for a 64-slice CT bypass graft study was 18.9 +/- 6.0 mSv (CTDIvol 42.3 +/- 12.9 mGy). The application of anatomically adapted tube current modulation had no effect on dose parameters (CTDIvol 43.3 +/- 13.2 vs. 40.1 +/- 12.1 mGy for those with versus those without anatomically adapted tube current modulation, P = 0.1). Additional implementation of ECG-controlled tube current modulation resulted in reduced dose parameters (CTDIvol of 32.9 +/- 2.6 vs. 58.9 +/- 3.9 mGy and radiation dose estimates: 14.7 +/- 1.9 mSv vs. 26.5 +/- 2.1 mSv for those with versus those without ECG pulsing, both P < 0.01). There was no deterioration in image quality with use of tube current modulation algorithms. CONCLUSIONS: The radiation burden associated with 64-slice bypass graft CT angiographies is substantial. Anatomically adapted tube current modulation does not reduce radiation dose parameters, whereas ECG-controlled tube current modulation was associated with a 45% reduction in dose estimates. Application of both tube current modulation algorithms did not result in reduced image quality.