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Virtual Monochromatic Imaging in Patients with Intermediate to High Likelihood of Coronary Artery Disease

Posted Nov 30, 2016 Updated Apr 10, 2023
By Patricia Carrascosa MD PhD FSCCT , Jonathon A. Leipsic MD FSCCT , Alejro Deviggiano MD , Carlos Capunay MD , Javier Vallejos MD , Alejro Goldsmit MD , Macarena C. De Zan MD , Gaston A. Rodriguez-Granillo MD PhD FACC
10 min read

Rationale and Objectives

We sought to explore the image quality and diagnostic performance of virtual monochromatic imaging derived from dual-energy computed tomography coronary angiography (DE-CTCA) in patients with intermediate to high likelihood of coronary artery disease (CAD) and the influence of calcification.

Materials and Methods

Consecutive symptomatic patients with suspected CAD referred for invasive coronary angiography who underwent DE-CTCA and a coronary artery calcium scoring before the invasive procedure comprised the study population.

Results

Sixty-seven patients were included. Image quality was significantly lower at 45 keV reconstructions (mean Likert score 45 keV 3.57 ± 0.6, 65 keV 4.07 ± 0.5, and 85 keV 4.09 ± 0.6; P < .0001). Patients with moderate calcification showed a trend toward a significant improvement in the diagnostic performance with 65 keV vs 45 keV reconstructions (45 keV, area under the curve 0.92 [95% confidence interval 0.89–0.95] vs 65 keV, area under the curve 0.96 [95% confidence interval 0.93–0.98], P = .06). The diagnostic performance of DE-CTCA was significantly lower in segments with higher coronary artery calcium scoring compared to segments with none or mild calcification, independent of the energy level applied.

Conclusions

In patients with intermediate to high likelihood of CAD, DE-CTCA had a good diagnostic performance, although significantly lower in segments with severe calcification.

Introduction

Computed tomography coronary angiography (CTCA) has been established as a valuable noninvasive diagnostic tool for the assessment of symptomatic patients with low to intermediate likelihood of coronary artery disease (CAD) . Notwithstanding, patients with intermediate to high likelihood of CAD have been consistently excluded from clinical studies involving this technology and consequently from diagnostic algorithms. To some extent, this has been attributed to the intricate distinction between heavily calcified plaques and luminal opacification that hamper the precise quantification of coronary stenosis . Calcified plaques usually seem larger on conventional single-energy computed tomography due to a number of technical issues such as blooming, beam hardening, and partial-volume effects, frequently leading to false-positive findings and therefore to potential unnecessary referral to invasive angiography .

Virtual monochromatic imaging derived from dual-energy computed tomography coronary angiography (DE-CTCA) shows promise to attenuate some of the aforementioned limitations and therefore might provide a more accurate assessment of high-risk patients . Briefly, the basic principle of DE-CTCA is the acquisition of two datasets from the same anatomic location with different kVp, which allows for synthesized monochromatic image reconstructions at different energy levels ranging from 40 to 140 keV. Although at the expense of higher image noise and blooming, lower energy levels yield higher intraluminal enhancement that allows a substantial iodine volume load reduction . In contrast, higher energy levels not only render a reduction in image noise and blooming but are also associated with significant reduction in luminal attenuation. We therefore sought to evaluate the image quality and diagnostic performance of DE-CTCA and the influence of different energy levels and extent of coronary calcification to accurately detect coronary stenosis in patients with intermediate to high likelihood of CAD.

Methods

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Image Acquisition

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Image Analysis

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Statistical Analysis

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Results

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Table 1

Demographical Characteristics ( n = 67)

N (%) Age (years ± SD) 61.3 ± 11.1 Male (%) 51(70%) Body mass index (kg/m 2 ) 28.3 ± 3.4 Diabetes (%) 14(21%) Hypertension (%) 47(70%) Hypercholesterolemia (%) 45(67%) Smoking (%) 38(57%) Previous myocardial infarction (%) 16(23%) Left ventricular ejection fraction (% ± SD) 57.3 ± 13.4 Systolic blood pressure (mmHg ± SD) 141.8 ± 21.8 Diastolic blood pressure (mmHg ± SD) 86.7 ± 13.0 Heart rate (bpm ± SD) 63.4 ± 8.3 Agatston calcium score (median, IQR) 597(184–1095)

bpm, beats per minute; IQR, interquartile range; SD, standard deviation.

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Figure 1, Diagnostic performance of dual energy-computed tomography coronary angiography. LR, likelihood ratio; NPV, negative predictive value; PPV, positive predictive value.

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Figure 2, Diagnostic performance of DE-CTCA according to the extent of calcification (CACS) on a per segment basis. CACS, coronary artery calcium scoring; DE-CTCA, dual-energy computed tomography coronary angiography; LR, likelihood ratio; NPV, negative predictive value; PPV, positive predictive value; Sen, sensitivity; Sp, specificity.

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Figure 3, Receiver operating characteristic analysis for the detection of obstructive coronary artery disease according to CACS tertile and energy level. CACS, coronary artery calcium scoring.

Figure 4, Maximum intensity projection (MIP) reconstructions of the right coronary artery in a 63-year-old woman with hypertension, hypercholesterolemia, and smoking as coronary risk factors and typical chest pain. The vessel is diffusely calcified and totally occluded at the mid segment ( arrow ). A patient-level Likert scale of 4 was assigned for 45, 65, and 85 keV reconstructions. Distal flow is provided by collateral circulation from the right ventricular branch. Reconstructions at increasing energy levels (45 keV, 65 keV, and 85 keV) are provided, showing that the segment with severe calcification (*) remains nonassessable independently of the energy level applied, although a minimal lumen area can be observed at the highest energy levels (L). At invasive coronary angiography (right panel), the total occlusion is confirmed, whereas the segment with diffuse calcification has only a mild to moderate stenosis.

Figure 5, Curved multiplanar reconstructions of the right coronary artery in a 62-year-old man with hypertension and hypercholesterolemia as coronary risk factors, with typical chest pain. A focal suboclusive (~99% stenosis) predominantly noncalcified lesion is identified at the mid segment (*). Reconstructions at increasing energy levels (45 keV, 65 keV, and 85 keV) are provided, showing that the severity of the stenosis remains unchanged independently of the energy level applied. A patient-level Likert scale of 4 was assigned for 45, 65, and 85 keV reconstructions. Invasive coronary angiography (right panel) confirms the lesion.

Figure 6, Curved multiplanar reconstructions of the left anterior descending artery in a 68-year-old man with hypercholesterolemia, atypical chest pain, and inconclusive stress test. An intermediate noncalcified lesion (arrow) is observed at the proximal segment. Reconstructions at increasing energy levels (45 keV, 65 keV, and 85 keV) show similar degree of stenosis independently of the energy level applied. A patient-level Likert scale of 4 was assigned for 45, 65, and 85 keV reconstructions. A focal eccentric calcified lesion is identified at the mid segment. Reconstructions at low energy levels (45 keV) depict apparently larger plaque size and smaller lumen area, whereas reconstructions at mid and higher (65 keV and 85 keV) energy levels confirm the minimal size of the lesion. Invasive coronary angiography identified no apparent lesion at such site.

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Discussion

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Conclusions

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Academic Radiology, Volume 23, Issue 12
Journals General Radiology
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