Rationale and Objectives. Concerns for patient’s risk of radiation-induced cancer have increased demand for reduced-dose coronary computed tomography angiography (CCTA). Previous comparisons of full and reduced-dose CCTA were not conclusive, because results were compared in different groups of patients. Presented here are results in patients examined by a widely used full dose CCTA protocol
and a new low-dose alternative.

Materials and Methods. Standard full-dose and low-dose CCTA with tube voltages of 120/100 kV were applied on 70 patients with intermediate probability of coronary artery disease (CAD). Both protocols used prospective electrocardiogram-gated acquisition on a 320-detector row CT scanner, whereas at low-dose CCTA the phase window was increased from 10% to 75% of R-R interval.

Results. Despite a mean dose reduction of 80%, from 4.9 +- 0.98 to 0.98 +- 0.24 mSv, visual image quality was not significantly affected at the low-dose protocol. Contrast level, image noise, and CNR for both protocols were similar in the majority of coronary segments. CNR for standard and low-dose protocol were 23.7 +- 17.1 and 23.2 +- 26.8, P = NS. Correlation between visual image quality and heart rate variability was strong at low dose: r = -0.58, P = .01, and absent at full dose: r = -0.07, P = .77.

Conclusion. Image quality of blood vasculature is generally not affected by 80% CCTA dose reduction applied to standard prospective electrocardiogram-gated acquisition. The performance at the low-dose protocol owes to the increased phase window, enhancing image quality at the cost of sensitivity to heart rate variability as compared with standard CCTA.

Key Words. Angiography; coronary arteries; contrast-to-noise ratio; radiation dose; 320-row computed tomography.

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