The research, led by Yuting Wen, Wanjiang Li, Xuelin Pan, Hangjia Hu and corresponding author Zhenlin Li of the Department of Radiology, with Xiaodi Zhang of Philips Healthcare, set out to answer a deceptively simple question: at which virtual monoenergetic energy level does spectral CT angiography best quantify coronary stenosis in patients whose arteries are burdened with calcified plaque? The team prospectively enrolled 42 patients with clinical suspicion of coronary atherosclerosis. Each participant underwent coronary CT angiography using a dual-layer spectral CT scanner and then completed invasive coronary angiography within four weeks, allowing the researchers to compare every imaging reconstruction against the reference standard in the same patients.

Dual-layer spectral CT, sometimes called detector-based spectral imaging, works differently from a conventional scanner. Instead of a single detector registering a blended X-ray spectrum, it stacks two detector layers that simultaneously record low- and high-energy photons from every projection. Software can then synthesize virtual monoenergetic images, or VMIs, which simulate how the anatomy would look if it were imaged with X-rays of a single, pure energy level measured in kiloelectron volts, or keV. At low energies around 40 keV, iodine contrast in the vessel lumen glows brightly, but beam hardening and noise increase. At high energies approaching 190 keV, calcium’s blooming shrinks and streak artifacts fade, but the iodine signal weakens and images can become washed out. Somewhere in between lies a sweet spot, and finding it for calcified coronary arteries was the study’s central goal.

In this trial, the researchers reconstructed conventional 120 kVp images along with virtual monoenergetic images spanning 40 to 190 keV at 30 keV intervals, all at the optimal cardiac phase on a dedicated post-processing workstation. They then compared image quality and vascular stenosis measurements across the multiple reconstruction groups, both between groups and within the same patients. Objective indicators such as signal-to-noise ratio and contrast-to-noise ratio were analyzed with one-way analysis of variance, followed by Tukey’s Honestly Significant Difference test for pairwise comparisons. Subjective image quality scores, assigned by radiologists assessing diagnostic confidence, artifacts and vascular visualization, were evaluated with the Friedman test. Two independent radiologists graded the images, and their inter-observer agreement was measured with Cohen’s weighted kappa, where values of 0.75 or above indicate excellent agreement.

The headline result is striking. Bland-Altman analysis, a statistical technique for quantifying agreement between two measurement methods, showed no significant difference between stenosis rates measured on 100 keV virtual monoenergetic images and those obtained from invasive coronary angiography, with a P value of 0.726. The bias rate of the 100 keV reconstructions was only approximately 0.1 percent, meaning the noninvasive measurements deviated from the catheter-based gold standard by a vanishingly small margin on average. By contrast, conventional 120 kVp images carried a bias rate of 10.3 percent, a discrepancy large enough to change clinical decisions in borderline cases. The improvement achieved by the 100 keV setting averaged 10.2 percentage points, a difference the authors report as statistically significant at P less than 0.01.

Image quality metrics told a consistent story. Significant differences in image quality were observed between the conventional 120 kVp images and every virtual monoenergetic group, all with P values below 0.01. Among the spectral reconstructions, the 100 keV images earned the highest subjective scores, reaching 4.81 plus or minus 0.40 on the rating scale for diagnostic confidence, image artifacts and vascular visualization, again with P less than 0.01. In practical terms, radiologists found that vessels surrounded by calcium were easier to trace, artifacts were less distracting, and they felt more confident rendering a diagnosis from the 100 keV series than from any alternative. Cohen’s weighted kappa values between the two observers all exceeded 0.75, confirming that this confidence was not the product of one reader’s idiosyncratic eye but a reproducible property of the images themselves.

The physics behind the result is worth unpacking. Calcified plaque and iodinated contrast differ in how their X-ray attenuation changes with photon energy. Calcium’s attenuation falls steeply as energy rises, so at 100 keV the bright halo around a calcified nodule contracts considerably, letting the contrast-opacified lumen behind it show through. Iodine, meanwhile, retains enough attenuation at 100 keV to keep the arterial lumen clearly delineated, even though its signal is weaker than at 40 or 70 keV. The 100 keV level therefore balances two competing demands: suppressing the calcium blooming that inflates apparent stenosis, while preserving the iodine contrast that defines the vessel wall and lumen. Lower energy reconstructions, despite their luminous iodine signal, amplify the very artifacts that distort stenosis grading in calcified segments, while higher energies sacrifice too much luminal contrast to remain diagnostically reliable.

The clinical implications are considerable. Invasive coronary angiography remains the reference standard for defining coronary stenosis, but it involves arterial catheterization, iodine loads, radiation exposure, procedural risk and cost, and it is not justified as a screening tool. Coronary CT angiography is noninvasive, fast and widely available, yet calcified plaques, which are common in older patients and in those with diabetes or chronic kidney disease, have long limited its accuracy, sometimes forcing patients into the catheterization laboratory on the basis of overestimated narrowing. If spectral CT scanners can routinely reconstruct 100 keV images that track invasive measurements within a fraction of a percent on average, the noninvasive test becomes substantially more trustworthy for the large population of patients with calcified coronary disease, potentially sparing some from unnecessary invasive procedures while ensuring that truly significant stenoses are not underestimated.

The study does have boundaries worth noting. Forty-two patients is a modest sample, and the cohort consisted of individuals with clinical suspicion of coronary atherosclerosis at a single center, so larger multicenter validation will be needed before the 100 keV recommendation becomes universal practice. The analysis focused on stenosis quantification in calcified plaques rather than on plaque characterization, ischemia prediction or outcomes, and the scanners, reconstruction software and reader expertise at West China Hospital may not translate identically to every imaging environment. The work was supported by the 1.3.5 project for disciplines of excellence at West China Hospital, Sichuan University, and the authors declare no competing interests. The article was published open access under a Creative Commons license, received by the journal on 15 July 2026, accepted on 28 August 2026 and published on 11 September 2026.

Even so, the findings land at a moment when spectral CT is spreading rapidly through hospital radiology departments, and they offer an unusually concrete, actionable takeaway: when quantifying coronary stenosis in the presence of calcified plaque, reconstruct and read the 100 keV virtual monoenergetic images. The study demonstrates that a single, well-chosen energy level can convert spectral CT from an imaging novelty into a measurement instrument whose numbers align with the catheter lab. For patients, that could mean fewer ambiguous reports and fewer unnecessary invasive procedures. For radiologists and cardiologists, it supplies an evidence-based default setting for one of coronary imaging’s most stubborn problems. As dual-layer detectors become standard equipment, the humble kiloelectron volt dial, tuned to 100 keV, may quietly become one of the most consequential settings in cardiac imaging.

Subject of Research: Determining the optimal virtual monoenergetic energy level of dual-layer spectral CT angiography for quantifying coronary stenosis in patients with calcified coronary plaques.

Article Title: Optimal virtual monoenergetic energy level of dual-layer spectral CT angiography for coronary stenosis quantification in patients with calcified coronary plaques: a prospective study

Article References: Wen, Y., Li, W., Pan, X., Hu, H., Zhang, X., & Li, Z. (2026). Optimal virtual monoenergetic energy level of dual-layer spectral CT angiography for coronary stenosis quantification in patients with calcified coronary plaques: a prospective study. BMC Medical Imaging. https://doi.org/10.1186/s12880-026-02746-w

Image Credits: AI Generated

DOI: 10.1186/s12880-026-02746-w

Keywords: spectral CT, coronary CT angiography, calcified plaque, coronary stenosis, virtual monoenergetic images, dual-layer detector, invasive coronary angiography, image quality, blooming artifact, BMC Medical Imaging, radiology, atherosclerosis