Abstract
Rationale and Objectives: Despite the recent development of coronary computed tomography angiography (CCTA) allowing for significant radiation dose reductions, the impact of lower tube voltages compared to traditional voltages is still unclear. We investigate the role of decreasing tube voltage and its effect on the total dose reduction and image quality.
Materials and Methods: We investigated 184 consecutive patients (age: 61±13 years; 47% male) referred for CCTA. Signal and noise [Hounsfield Units (HU)] were measured in the ascending aorta at the level of the left main origin. The contrast was calculated by [signal - HU measured in subcutaneous tissue in front of the sternum]. The signal-to-noise ratio (SNR) was calculated by [signal / noise] and the contrast-to-noise ratio (CNR) was calculated by [contrast / noise]. Signal, noise, contrast, the dose length product (DLP) and radiation dose (millisievert: mSv) were assessed between the kilovoltage (kVp) protocols. Images were scored qualitatively by two experienced readers.
Results: Body mass index was significantly higher in the 120-kVp patients than in the 100- and 80-kVp patients (29.9±3.1 vs. 26.1±3.1 vs. 22.7±2.0; p<0.0001). Retrospective protocols were used in 10.5%, 10.8% and 18.2% for 120-, 100- and 80- kVp patients, respectively. Overall, a post-processing algorithm called adaptive statistical iterative reconstruction (IR 30%) was used in 58% of patients. The radiation doses were 3.3, 1.9 and 1.0 mSv for the 120-, 100- and 80-kVp protocols (p<0.0001 for both), respectively. When compared with the 120-kVp protocol, lower tube voltages with 100 and 80 kVp were associated with an increased signal, higher contrast and increased noise with resultant increase in the SNRs (10.7±3.2 vs. 12.2±3.6 vs. 12.2±3.2; p<0.0001) and CNRs (7.8±2.5 vs. 9.5±3.5 vs. 9.7±2.8; p=0.0002), respectively. Image quality showed no significant difference among the kVp groups (p=0.243).
Conclusion: A tube voltage reduction from the standard 120-kVp to 100- or 80-kVp protocols provided a total dose saving of 42% or 67%, respectively, without sacrificing image quality. We should consider more widespread use of lower tube voltages for patients who undergo CCTA to minimize radiation exposure.
Keywords: cardiac computed tomography angiography, kVp, noise, radiation reduction, signal.
Graphical Abstract
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