Introduction and Purpose
Computed tomography coronary angiography (CTCA) is a pivotal, noninvasive tool for evaluating coronary artery disease. A key clinical challenge is balancing diagnostic image quality with patient radiation dose. This study analyzes how tube voltage (kVp) affects image quality and radiation dose, comparing 100 kVp and 120 kVp protocols in a BMI-based approach.
Methods and Population
In this prospective observational study conducted from June 2023 to December 2023 at the Department of Radio Diagnosis and Imaging, Kasturba Hospital, Manipal, India, 88 adults scheduled for CTCA were enrolled after ethical approval and informed consent. Participants were divided by BMI: < 25 kg/m2 underwent 100 kVp scanning, while ≥ 25 kg/m2 received 120 kVp. Each group included 44 patients. Heart rate was controlled to below 70 bpm with beta-blockers when needed, and sublingual nitroglycerine was used to enhance coronary dilation as tolerated.
CT Protocol and Image Acquisition
All scans were performed on a 128-slice MDCT with retrospective ECG gating. Voltage settings followed the BMI-based protocol, while image reconstruction used standard techniques. Cardiac phases with minimal motion artifacts were selected for analysis.
Image Analysis and Endpoints
Image quality was assessed both quantitatively and qualitatively. Quantitative metrics included tissue density in Hounsfield units (HU), image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). ROIs were placed on the aorta and major coronary arteries (RCA, LM, LAD, LCX). Definitions used were:
- Image noise = SD of tissue density
- SNR = vascular density ÷ density (air)
- CNR = (vascular density − muscle density) ÷ density (air)
Qualitative analysis, performed by two blinded radiologists, used a 4-point Likert scale (1 non-diagnostic to 4 excellent) focusing on delineation, density, and distal opacification. Interreader reliability was evaluated to ensure robustness of subjective assessments.
Radiation Dose Assessment
Radiation dose was estimated using the dose length product (DLP) collected from the scanner, applying the standard chest conversion factor (k = 0.014 mSv/mGy·cm) to derive the effective dose. This allowed direct comparison of patient exposure between the 100 kVp and 120 kVp groups.
Key Findings
The study demonstrated that lowering tube voltage to 100 kVp in leaner patients provided substantial radiation dose reduction—approximately 39% less than 120 kVp—without compromising diagnostic image quality. In patients with BMI ≥ 25 kg/m2 scanned at 120 kVp, image noise was higher, yet CNR and SNR remained clinically acceptable due to higher attenuation from the iodinated contrast and the ability to optimize mAs where needed.
Quantitative Outcomes
Compared across groups, 100 kVp protocols yielded higher HU values in arterial ROIs at similar or reduced contrast enhancement, improving vessel conspicuity in lean individuals. However, at 120 kVp, there was a consistent decrease in HU values alongside reduced background noise, illustrating the classic trade-off between contrast and noise with voltage changes. Overall, CNR and SNR remained in the acceptable diagnostic range for both protocols, with subtle advantages favoring 100 kVp in lower BMI patients.
Qualitative Assessment
Radiologists reported comparable diagnostic confidence for both protocols, with substantial interreader agreement. Even with lower kVp, the ability to delineate vessels and detect potential plaques remained robust, underscoring the feasibility of BMI-guided voltage selection in routine practice.
Clinical Implications and Practical Considerations
These findings support a BMI-based approach to tube voltage selection in CTCA, enabling meaningful radiation dose reductions without sacrificing image quality. This has particular relevance in centers where retrospective ECG gating is used, or where dose reduction strategies are prioritized. The study also highlights the potential role of advanced iterative reconstruction algorithms in further mitigating noise at 100 kVp, especially for patients with higher BMI.
Limitations and Future Directions
Limitations include single-center design and a modest sample size. Retrospective ECG gating in this study commonly yields higher doses than prospective gating, potentially inflating dose differences. Future multicenter trials with larger cohorts, prospective gating, and exploration of advanced reconstruction techniques will help validate and refine BMI-based voltage optimization across diverse patient populations.
Conclusion
Optimizing tube voltage according to BMI can substantially reduce radiation exposure in CT coronary angiography while preserving diagnostic image quality. A 100 kVp protocol for low-BMI patients and a 120 kVp protocol for higher-BMI patients provide a practical, implementable strategy to balance patient safety with accurate coronary visualization.
