Image Quality and Radiation Dose of Pulmonary CT Angiography Performed Using 100 and 120 kVp

OBJECTIVE. The objective of our study was to compare image quality and radiation dose of pulmonary CT angiography (CTA) performed in the same patient cohort using tube potentials of 100 and 120 kVp. MATERIALS AND METHODS. The study group for this retrospective study was 32 patients (22 women, 10 men) with a mean age of 57 years (age range, 28-83 years; body weight < 100 kg). Patients underwent pulmonary CTA studies performed using 120 and 100 kVp while other scanning parameters were kept constant. Two observers measured image signal and image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), and SNR dose and CNR dose. Two additional observers performed qualitative image quality analysis using a 5-point grading scale (5 = excellent). RESULTS. The reduction in tube potential caused image signal to increase by 29% (p < 0.0001), image noise to increase by 68% (p < 0.0001), CNR dose to decrease by 0.8% (p = 0.91) and SNR to decrease by 24% (p = 0.0002) and CNR by 20% (p = 0.0019). Radiation dose (dose-length product) was decreased by 37% to 379.26 mGy x cm at 100 kVp from 604.46 mGy x cm at 120 kVp (p < 0.0001). The median pulmonary arteries image quality scores for observers 1 and 2, respectively, were as follows at 100 kVp: main, 5 and 5; lobar, 5 and 4.5; and segmental, 5 and 4. At 120 kVp, the median image quality scores for observers 1 and 2 were as follows: main, 5 and 5; lobar, 5 and 5; segmental, 4 and 4. A Wilcoxon test analysis indicated no significant difference in image quality between the studies (main, p = 0.59; lobar, p = 0.88; segmental, p = 0.79). CONCLUSION. Pulmonary CTA can be performed using a tube potential of 100 kVp in patients who weigh less than 100 kg (220 lb). Reducing the tube potential from 120 to 100 kVp results in a 37% reduction in radiation dose without a significant impact on diagnostic image quality.