Radiation dose and image quality at high-pitch CT angiography of the aorta: intraindividual and interindividual comparisons with conventional CT angiography.

OBJECTIVE: The objective of our study was to evaluate radiation dose and quantitative image quality parameters at high-pitch CT angiography (CTA) of the aorta compared with conventional CTA. MATERIALS AND METHODS: We studied the examinations of 110 patients (65 men and 45 women; mean age ± SD, 64 ± 15 years) who had undergone CTA of the entire aorta on a second-generation dual-source CT system; 50 examinations were performed in high-pitch mode. The mean arterial attenuation, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure of merit (FOM) were calculated for the high-pitch CTA and conventional CTA groups. Radiation exposures were compared. RESULTS: All studies were considered of diagnostic quality. At high-pitch CTA, the mean tube voltage and tube current-exposure time product were 118 ± 7 kV (SD) and 197 ± 78 mAs compared with 120 ± 1 kV and 258 ± 78 mAs, respectively, at conventional CTA (p < 0.05). The mean volume CT dose index, dose-length product, and effective dose were 8.1 ± 2.4 mGy, 561.1 ± 178.6 mGy × cm, and 9.6 ± 3.0 mSv at high-pitch CTA and 18.3 ± 7.7 mGy, 1162.6 ± 480.1 mGy × cm, and 19.8 ± 8.2 mSv at conventional CTA (p < 0.001). Attenuation was similar for both protocols, whereas significantly less contrast medium was injected for high-pitch CTA than for standard-pitch CTA (87.3 ± 16 mL vs 97.9 ± 16 mL, respectively; p < 0.01). The SNR and CNR were significantly lower in the high-pitch CTA examinations (p < 0.01), whereas the FOM was nonsignificantly higher. Twenty patients underwent both high-pitch CTA and conventional CTA, with a 45% reduction in radiation dose (p < 0.001). CONCLUSION: High-pitch CTA of the aorta yields 45-50% reduction of radiation exposure as well as contrast medium savings with maintained vessel attenuation.

Impact of ventricular contrast medium attenuation on the accuracy of left and right ventricular function analysis at cardiac multi detector-row CT compared with cardiac MRI.

RATIONALE AND OBJECTIVES: The aim of this study was to investigate the impact of ventricular contrast medium attenuation on the accuracy of left ventricular (LV) and right ventricular (RV) function analysis on coronary computed tomographic angiographic (CCTA) imaging compared to cardiac magnetic resonance imaging (CMR). MATERIALS AND METHODS: Thirty patients (mean age, 61.9 ± 11.2 years; 14 men) underwent CCTA imaging and CMR. For both the right and left ventricles, end-diastolic volume (EDV), end-systolic volume (ESV), and stroke volume (SV) were computed using multiphase image reconstruction of CCTA data. The accuracy of CCTA imaging was determined by subtracting CCTA measurements from CMR measurements. The accuracy of CCTA imaging was then correlated with the level of LV and RV contrast medium attenuation using regression analysis. RESULTS: In the right ventricle, there was strong correlation between the accuracy of CCTA functional assessment of EDV (R(2) = 0.78, P < .001), ESV (R(2) = 0.36, P < .001), and SV (R(2) = 0.75, P < .001) and the level of RV contrast medium attenuation. In studies with lower RV enhancement (<176 Hounsfield units; n = 15), the mean CCTA deviations of EDV, ESV, and SV from CMR measurements were 43.6 ± 17.4, 11.2 ± 9.64, and 35.1 ± 11.5 mL, respectively. In studies with higher RV attenuation (>176 Hounsfield units; n = 15), these values were 13.6 ± 10, 8.0 ± 5.28, and 13 ± 4.96 mL, respectively. In the left ventricle, there was weak correlation between functional CCTA accuracy and LV attenuation (mean, 358.31 ± 68.71 Hounsfield units), and there was excellent correlation with CMR for LV EDV (R(2) = 0.86, P < .001), ESV (R(2) = 0.85, P < .001), and SV (R(2) = 0.51, P < .001). CONCLUSIONS: If computed tomographic evaluation of RV function is desired, attention should be paid to the contrast injection protocol, because the accuracy of RV function analysis depends on the level of contrast medium attenuation. The high contrast medium attenuation that is typically achieved in the left ventricle routinely enables highly accurate measurements compared to CMR.