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Dual-Source CT in Step-and-Shoot Mode: Noninvasive Coronary Angiography with Low Radiation Dose¹

¹ From the Institute of Diagnostic Radiology (P.S., S.L., H.S., T.K., L.D., B.M., H.A.) and Clinic for Cardiovascular Surgery (A.P., M.G.), University Hospital Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland; Computed Tomography CTE PA, Siemens Medical Solutions, Forchheim, Germany (T.G.F.); and Institute of Radiology, Kantonsspital St Gallen, St Gallen, Switzerland (S.W.). Received November 20, 2007; revision requested January 20, 2008; revision received February 1; accepted March 3; final version accepted March 28. Supported by the National Center of Competence in Research, Computer Aided and Image Guided Medical Interventions (NCCR CO-ME) of the Swiss National Science Foundation. Address correspondence to H.A. (e-mail: hatem.alkadhi{at}usz.ch).

Purpose: To prospectively investigate computed tomographic (CT) image quality parameters by using different protocols and to calculate radiation dose estimates for noninvasive coronary angiography performed with dual-source CT in the step-and-shoot (SAS) mode.

Materials and Methods: This study was local ethics board approved; written informed consent was obtained from all patients. In the preliminary portion of the study, 40 patients underwent CT coronary angiography in the SAS mode: at 100 kV (protocol A) in 22 patients with a body mass index (BMI) of less than 25 kg/m² and at 120 kV (protocol B) in 18 patients with a BMI of 25–30 kg/m². Both protocols involved use of an attenuation-based tube current and 1 mL of contrast material per kilogram of body weight. The final portion of the study involved 50 additional patients: 21 patients with a BMI of 25–30 kg/cm² assigned to protocol B and 29 patients with a BMI of less than 25 kg/cm² assigned to protocol C, which was performed with 100 kV, an attenuation-based tube current, and a reduced contrast material dose of 0.8 mL/kg. Image quality was independently assessed. Attenuation in the aorta and coronary arteries and image noise were measured. Radiation dose was estimated.

Results: Mean image noise was similar with protocols A and B. Mean attenuation in the aorta and coronary arteries with protocol A (444 HU) was significantly (P < .001) higher than that with protocol B (358 HU). The reduced contrast material dose in protocol C yielded attenuation similar to that with protocol B. Diagnostic image quality was achieved with all protocols in 1237 (97.9%) of 1264 coronary segments. No significant differences in image quality between the 100- and 120-kV protocols were found. Mean heart rate had a significant effect on motion artifacts (area under receiver operating characteristic curve [AUC] = 0.818; 95% confidence interval [CI]: 0.723, 0.892; P < .001), whereas heart rate variability had a significant effect on stair-step artifacts (AUC = 0.79; 95% CI: 0.687, 0.865; P < .001). The mean estimated effective dose was 1.2 mSv ± 0.2 for protocols A and C and 2.6 mSv ± 0.5 for protocol B.

Conclusion: Dual-source SAS-mode CT coronary angiography yielded diagnostic image quality for 97.9% of coronary segments at a low radiation dose.

© RSNA, 2008

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