Image quality and radiation exposure at pulmonary CT angiography with 100-or 120-kVp protocol: prospective randomized study

Purpose:To prospectively compare 16- section multidetector computed tomography ( CT) at 100 and 120 kVp for image quality and radiation dose. Materials and Methods: The study had institutional review board approval; written informed consent was obtained. Sixty patients were referred for evaluation of suspected pulmonary embolism with CT angiography. Patients were randomly assigned to a 100- kVp ( n = 30; 17 men, 13 women; mean age, 66 years +/- 17 [ standard deviation]; range, 19 - 89 years) or 120- kVp ( n = 30; 15 men, 15 women; mean age, 62 years +/- 15; range, 28 - 86 years) protocol. Other scanning parameters were kept constant. Contrast medium was injected automatically with bolus tracking. Pulmonary vessel enhancement and image noise were quantified; signaltonoise ratio ( SNR) and contrast- to- noise ratio ( CNR) were calculated. Subjective vessel contrast was assessed by two radiologists in consensus. Effective dose was calculated on the basis of dose length product and volume CT dose index. Results of both protocols were compared by using the X-2 test and Student t test. Results: The 100- kVp protocol had a nonsignificantly higher mean vessel attenuation than the 120- kVp protocol ( 386.8 HU +/- 130.1 vs 317.9 HU +/- 112.5; P =.56) and a nonsignificantly higher image noise ( 16.9 HU +/- 5.8 vs 13.7 HU +/- 6.2; P =.84), which resulted in almost identical SNR ( 25.3 +/- 11.7 vs 27.0 +/- 14.5; P =.37) and CNR ( 22.0 +/- 11.2 vs 22.9 +/- 13.1; P =.51). There was no significant difference in subjective image quality between protocols. Mean effective dose for the 100- kVp protocol was significantly lower than that for the 120- kVp protocol ( 1.37 mSv +/- 0.39 vs 2.44 mSv +/- 0.97; - 44%; P <.001). Conclusion: Reduction of kilovoltage from 120 to 100 kVp resulted in significant reduction of effective dose at pulmonary CT angiography, without significant loss of objective or subjective image quality.