Impact on image quality and radiation exposure in coronary CT angiography: 100 kVp versus 120 kVp

Abstract

The risk of radiation-induced cancer has become a major concern with the increasing use of computed tomography (CT). To compare image quality and radiation doses when decreasing X-ray tube peak kilovoltage (kVp) from 120 to 100 kVp in patients undergoing coronary CT angiography (CCTA). Patients referred for evaluation of suspected coronary artery disease (CAD) underwent 64-channel detector CCTA using a tube voltage of either 120 kVp (n = 46) or 100 kVp (n = 82). The individual volume CT dose index (CTDI(vol)) and dose length product (DLP) were recorded and effective radiation dose was estimated on the basis of DLP. Subjective image quality was assessed by two radiologists on per-patient based consensus. Vascular density and image noise were quantified in the left main coronary artery (LMCA) and proximal ascending aorta (AA). Mean density in the adjacent perivascular tissue was also quantified. Contrast-to-noise ratio (CNR) was calculated. Corresponding invasive coronary angiography (ICA) was performed, which constituted the gold standard. Mean values in the 100/120 kVp cohorts regarding CNR in the LMCA were 12.7/16.0 (P<0.0001)) and in the AA 13.2/17.2 (P<0.0001), CTDI(vol) 34.4/57.4 mGy (a 40% reduction, P<0.0001), DLP 578/1125 mGy × cm (P<0.0001), and estimated effective dose 9.6/20.2 mSv (P<0.0001). There was no statistically significant difference in subjective image quality between the two cohorts. The sensitivity to detect significant coronary stenoses was 88% (120 kVp) and 84% (100 kVp) and the specificity was 71% (120 kVp) and 74% (100 kVp), respectively. By reduction of tube voltage from 120 to 100 kVp at CCTA, while keeping all other scanning parameters unchanged, the radiation dose to the patient can be almost halved while keeping the diagnostic image quality at a clinically acceptable level.