Introduction
In CT coronary angiography (CTCA), balancing image quality with patient safety is essential. This observational study from Kasturba Hospital, Manipal, investigates how tube voltage—specifically 100 kVp versus 120 kVp—affects image quality and radiation exposure. By tailoring voltage to body mass index (BMI), researchers aim to achieve diagnostic-quality images while minimizing radiation dose.
Study design and methods
The prospective analysis enrolled 88 adults referred for CTCA between June and December 2023. Participants were divided into two BMI-based groups: those with BMI < 25 kg/m2 scanned at 100 kVp, and those with BMI ≥ 25 kg/m2 scanned at 120 kVp, with 44 participants per group. Beta-blockade was used to achieve heart rates below 70 bpm, and sublingual nitroglycerine was administered to optimize coronary vasodilation unless contraindicated. All procedures followed ethical guidelines and were registered with CTRI.
CT protocol and image acquisition
Scans were performed on a 128-slice MDCT scanner using standard cardiac protocols. Voltage settings were selected according to BMI, while image data focused on phases with minimal motion artifacts. The aim was to compare quantitative and qualitative image quality alongside dose metrics across the two voltage settings.
Quantitative image analysis
Measurements were taken in three ROIs across major vessels—the Aorta (AO), Right Coronary Artery (RCA), Left Main (LM), Left Anterior Descending (LAD), and Left Circumflex (LCX). Key metrics included tissue density in Hounsfield units (HU), image noise (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Formulas adhered to standard radiology practice, with SNR and CNR calculated relative to reference densities.
Qualitative and inter-reader assessment
Two radiologists, blinded to voltage settings, evaluated image quality on a 4-point Likert scale (1 non-diagnostic to 4 excellent). Emphasis was placed on delineation of coronary structures, lumen contrast, and distal opacification. Inter-reader reliability demonstrated substantial agreement, underscoring the robustness of qualitative findings across voltage protocols.
Radiation dose and safety evaluation
Effective dose was estimated from dose-length product (DLP) using a standard conversion coefficient. The study discusses how dose varies with voltage and gating technique, noting that retrospective ECG gating tends to yield higher exposures than prospective gating. The authors compare their results with existing literature and highlight how BMI-driven voltage selection can reduce dose while preserving diagnostic confidence.
Key findings
Lowering tube voltage from 120 kVp to 100 kVp in appropriate BMI groups yielded a notable reduction in radiation dose. The study reports a decrease in DLP and overall effective dose by approximately 39% when moving from 120 to 100 kVp, with a maintained capacity for diagnostic image quality. Qualitative assessments supported these findings, showing that image delineation and distal vessel visualization remained acceptable for clinical decision making in the BMI-stratified 100 kVp group.
Image quality metrics and clinical implications
Quantitatively, HU values tended to be higher at 100 kVp in arterial ROIs, reflecting greater contrast between lumen and vessel wall, which can facilitate plaque assessment. However, increased image noise at lower kVp can offset gains in contrast. The study notes that iterative reconstruction techniques (e.g., IR methods) can further mitigate noise, preserve edge detail, and enhance CNR/SNR at lower voltages. Although the current protocol used standard reconstruction, incorporating IR may broaden the applicability of 100 kVp in diverse BMI ranges.
Gating, protocol optimization, and limitations
The authors acknowledge that retrospective gating may contribute to higher baseline dose compared with prospective approaches. They emphasize that BMI-based voltage adjustment offers a practical, vendor-neutral strategy to reduce exposure without compromising interpretability. Limitations include single-center design and modest sample size; multicenter studies are needed to validate BMI-driven protocols across populations and equipment. Future work could explore patient subgroups and advanced reconstruction techniques to push dose reductions further.
Conclusion
This comparative study supports the feasibility of BMI-based voltage selection in CTCA, achieving substantial radiation dose reductions with preserved image quality. The findings advocate for a patient-tailored approach—using 100 kVp for lower BMI and 120 kVp for higher BMI—to optimize safety and diagnostic performance in coronary imaging.
