Radiation dose reduction by using 100-kV tube voltage in cardiac 64-slice computed tomography: a comparative study.

OBJECTIVE: To evaluate a 100-kilovoltage (kV) tube voltage protocol regarding radiation dose and image quality, in comparison with the standard 120 kV setting in cardiac computed tomography angiography (CCTA). METHODS: 103 patients undergoing retrospective ECG-gated helical 64-slice CCTA were enrolled (100 kV group: 51 patients; 120 kV group: 52 patients). Inclusion criteria were: (1) BMI <28 kg/m(2); (2) weight <85 kg; (3) coronary calcium score <300 Agatston Units (AU). Quantitative image quality parameters were calculated [image noise, contrast-to-noise ratio (CNR), intracoronary CT-attenuation (HU)]. Each coronary artery segment (AHA/ACC-16-segments-classification) was evaluated for image quality on a 4-point scale. RESULTS: There was no statistical difference in age, gender, BMI and eff. tube current (mAs), and the use of ECG-tube current modulation (50.9% vs. 50% of patients) between both groups. 84.2% of patients in the 100 kV group had zero calcium score or less than 100 AU, the remaining had between 100 and 300 AU. The effective radiation dose was significantly lower in the 100 kV group with mean 7.1 mSv+/-2.4 (range, 3.4-11.1) compared to the 120 kV group with 13.4 mSv+/-5.2 (range, 6.3-22.7) (p<0.001) (dose reduction, 47%). In the 100 kV group, the use of ECG-dependent tube current modulation reduced the radiation exposure (by 44.8%) to 5.3 mSv+/-1.1 (range, 3.4-8.5 mSv) (p<0.001), the dose without was 9.6 mSv+/-1.1 (range, 6.3-11.1). Image noise in the coronary arteries was not different between both groups with 29.8 and 30.5 SD [HU], respectively. CNR in the 100 kV group was with 20.9+/-6.8 for the coronary arteries and with 19.9+/-5.9 for the aorta similar to the 120 kV group. Intraluminal CT-attenuation (HU) of the coronary arteries were higher in the 100 kV group (p<0.001). Image quality on 100 kV scans was excellent in 86.3%, good in 9.2%, acceptable in 3.1% of coronary segments; 1.4% were non-interpretable (in 1/4 due to increased image noise because of BMI >25 kg/m(2)). CONCLUSIONS: The 100 kV protocol significantly reduces the radiation dose in CCTA in patients with a low BMI <25 kg/m(2) and a low calcium load while maintaining high image quality and the advantages of helical scan algorithm.

Clinical relevance and scope of accidental extracoronary findings in coronary computed tomography angiography: a cardiac versus thoracic FOV study.

OBJECTIVE: To assess the spectrum and clinical relevance of extracoronary findings in coronary CT angiography (CCTA), and to compare a small (cardiac) field of view (FOV) to a large (thoracic) FOV setting. MATERIAL AND METHODS: 1084 consecutive patients (mean 57 years) with low-to-intermediate risk of coronary artery disease were enrolled. 542 CCTA scans were interpreted with small FOV (160-190mm(2)) encompassing the cardiac region. In another 542 CCTA (patients matched for age and gender), read-out of an additional full FOV (>320mm(2)) covering the thorax was performed. Clinical relevance of extracoronary findings was considered as either "significant" or "non-significant". "Significant" findings were subclassified as either score 1: findings necessitating immediate therapeutic actions, or score 2: findings with undoubted clinical or prognostic relevance, requiring clinical awareness, follow-up or further investigations (non-urgent). "Non-significant" findings were assigned to either score 3: findings not requiring follow-up or further tests, or as score 4: irrelevant incidental findings. RESULTS: Significantly more patients with extracoronary findings were identified by using a full FOV with 43.2% (234/542) compared to a small FOV with 33.6% (182/542) (p=0.001). Similarly, a higher total number of extracoronary findings (n=394) was found on full FOV compared to small FOV (n=250) (p<0.001). The detection rate of clinically significant findings was higher by using full FOV compared to small FOV (25.6% versus 15.4%) (p<0.001), out of those 2.2% versus 1.8% of findings required immediate actions (score 1), and 23.4% versus 13.6% (p=0.0001), respectively were of clinical relevance (non-urgent, score 2). The rate of malign findings was 0.2%, and of acute pulmonary embolism 0.1%. More lung pathologies were observed by using full FOV compared to small FOV (22% versus 7%) (p<0.0001), and the detection rate of intrapulmonary nodules increased by 2.1%. Prevalence of aortic valve calcification (n=72) was 13.3%, out of those 7% had less than 2cm(2) aortic valve orifice area. CONCLUSIONS: The interpretation of extracoronary findings on CCTA scans is mandatory given high prevalence of clinically significant findings by using a full "thoracic" FOV.