Effect of Increasing Body Mass Index on Image Quality and Positive Predictive Value of 100-kV Coronary Computed Tomographic Angiography

Lowering the voltage to 100 kV is an effective method of reducing the radiation of coronary computed tomographic angiography (CTA). It is unknown, however, whether one could use a 100-kV CTA protocol with overweight or obese patients. We, thus, evaluated the effect of increasing body mass index (BMI) on various image quality parameters of 100-kV CTA. We also compared the radiation dose and diagnostic accuracy of 100-kV CTA with CTA performed at 120 kV. Three different protocols were studied: 120 kV, retrospective; 100 kV, retrospective; and 100 kV, prospective. The image quality and radiation doses were analyzed for each protocol. The effect of increasing BMI was also examined. A worsening of the noise, contrast-to-noise, and signal-to-noise ratios occurred with increasing BMI and decreasing voltages. The radiation exposure was significantly lowered with the 100-kV protocol and with prospective gating. Despite this image degradation, however, diagnostic images were obtained with 100-kV CTA, even in overweight and many obese subjects. Of the 66 subjects referred for invasive angiography because of the findings from CTA, 55 were correctly characterized (overall positive predictive value [PPV] of 83.3%). This PPV remained reasonable, irrespective of the voltage, until a BMI of 35 kg/m² was reached (PPV for 100-kV protocol 90.0% [27 of 30]; PPV for a BMI of ≥25 kg/m² but <30 kg/m² 84.4% [27 of 32]; and PPV for a BMI of ≥30 kg/m² but <35 kg/m² 81.8% [18 of 22]). In conclusion, 100-kV coronary CTA is feasible in overweight and many obese subjects.