Rationale and Objectives
Although intravascular ultrasound (IVUS) is the current gold standard for plaque characterization, noninvasive coronary computed tomographic angiography (CCTA) requires further evaluation. The ability to detect plaque morphology by CCTA remains unclear. The purpose of this study was to evaluate the diagnostic accuracy of CCTA for plaque detection and morphology.
Materials and Methods
Thirty-one patients underwent cardiac catheterization with IVUS and CCTA. The presence of plaque was evaluated by both modalities in nonocclusive segments (<50% stenosis) of the left anterior descending artery, left circumflex artery, and right coronary artery. Plaque morphology was classified as (1) normal, (2) soft or fibrous, (3) fibrocalcific, or (4) calcific. Results by IVUS and CCTA were compared blindly on a segment-to-segment basis with subgroup analysis based on CCTA tube voltage.
Results
Among the 31 patients (mean age 56.2 ± 8.6 years, 27% female), 152 segments were analyzed. Of these segments, 42% were in the left anterior descending artery, 32% were in the left circumflex artery, and 26% were in the right coronary artery. Plaque morphology by IVUS identified 103 segments as fibrous (68%), 31 as fibrocalcific (20%), and 6 as calcific (4.0%); 12 segments were normal (8.0%). To evaluate for the presence of plaque, CCTA had an overall sensitivity and specificity of 99% and 75%, respectively. In patients who underwent CCTA with a tube voltage of 100 kV, both sensitivity and specificity were 100%. The sensitivity and specificity of CCTA to identify plaque as calcified (fibrocalcific or calcific) vs noncalcified (soft or fibrous) were 87% and 96%, respectively. Overall, the accuracy of CCTA to detect the presence of plaque was 97%; the accuracy to detect plaque calcification was 94%.
Conclusions
CCTA offers excellent sensitivity and accuracy for plaque detection and morphology characterization in nonocclusive coronary segments. In addition, diagnostic accuracy is preserved with a reduced tube voltage protocol.
Introduction
Coronary computed tomographic angiography (CCTA) offers a noninvasive, anatomically based approach for the accurate assessment of coronary artery disease. Previous studies have already established coronary artery calcium as a surrogate for plaque burden and a predictor of future coronary events among a variety of populations in the United States . More than two-thirds of myocardial infarctions are now estimated to occur in coronary arteries with only moderate stenosis . There is also evidence that nonobstructive plaques play an important role in death . Therefore, focus has deservedly turned to the use and validation of CCTA to identify the presence of nonobstructive plaque and to characterize plaque type.
Intravascular ultrasound (IVUS) is the current gold standard for the assessment of coronary plaque morphology. Although invasive, IVUS provides superior plaque characterization and more accurate quantification of plaque burden compared to traditional coronary angiography. However, recent studies also indicate that CCTA can accurately assess plaque morphology in both obstructive and nonobstructive coronary segments . With this growing role, CCTA may be able to noninvasively detect “at-risk” or vulnerable plaques in nonobstructive coronary segments before the patient develops symptomatic disease in the form of myocardial infarction or sudden cardiac death. Moreover, lower-voltage CCTA protocols, which offer improved signal- and contrast-to-noise ratios, may enhance diagnostic accuracy for the detection of coronary plaque and plaque morphology with the added benefit of reduced radiation exposure to the patient .
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Materials and Methods
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Study Population
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Coronary Computed Tomographic Angiography
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Conventional ICA and IVUS
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Statistical Analyses
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Results
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Table 1
Plaque Morphology by CCTA and IVUS
Segment Classification
( n = 152) Imaging Method CCTA IVUS Normal 10 12 Plaque Soft or fibrous 106 103 Fibrocalcific 30 31 Calcific 6 6
CCTA, computed tomographic angiography; IVUS, intravenous ultrasound.
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Table 2
Sensitivity, Specificity, and Overall Accuracy of CCTA in the Detection of Plaque and Plaque Calcification Compared to IVUS
Normal vs Plaque Noncalcified vs Calcified Plaque Sensitivity (%) 99 (139/140) 87 (32/37) Specificity (%) 75 (9/12) 96 (99/103) Overall accuracy (%) 97 (148/152) 94 (131/140)
CCTA, computed tomographic angiography; IVUS, intravenous ultrasound.
Table 3
Statistical Comparison of CCTA Based on Tube Voltage Protocol
Tube Voltage 120 kV 100 kV Normal vs plaque Sensitivity (%) 99 (93/94) 100 (46/46) Specificity (%) 63 (5/8) 100 (4/4) Overall accuracy (%) 96 (98/102) 100 (50/50) Noncalcified vs calcified plaque Sensitivity (%) 89 (23/26) 82 (9/11) Specificity (%) 94 (64/68) 100 (35/35) Overall accuracy (%) 93 (87/94) 96 (44/46)
CCTA, computed tomographic angiography.
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Table 4
Hounsfield Unit Measurements Based on Tube Voltage Protocol and Plaque Type
Combined Group 120-kV Group 100-kV Group Fibrous or soft 102 ± 78 \* 114 ± 78 \* 80 ± 58 \* Fibrocalcific 331 ± 99 335 ± 99 309 ± 103 Calcific 944 ± 440 466 ± 440 1183 ± 343
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Discussion
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Study Limitations
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Conclusions
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Acknowledgment
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