The Perivascular Fat Attenuation Index Improves the Diagnostic Performance for Functional Coronary Stenosis

Abstract

Background: Coronary computed tomography angiography (CCTA) is an established first-line test in the investigation of patients with suspected coronary artery disease (CAD), while the perivascular fat attenuation index (FAI) derived from CT seems to be a feasible and efficient tool for the identification of ischemia. The association between the FAI and lesion-specific ischemia as assessed by fractional flow reserve (FFR) remains unclear. Methods: In a total of 261 patients, 294 vessels were assessed for CCTA stenosis, vessel-specific FAI, lesion-specific FAI, and plaque characteristics. The diagnostic accuracies of each parameter and the combined approach were analyzed via the receiver operating characteristic curve (ROC) with FFR as the reference standard. The determinants of FAI were statistically analyzed. Results: The cutoff values of vessel-specific FAI and lesion-specific FAI scores calculated according to the Youden index were −70.97 and −73.95 HU, respectively. No significant differences were noted between them; however, they exhibited a strong correlation. No significant differences were noted between the area under the curve (AUC) scores of vessel-specific FAI (0.677), lesion-specific FAI (0.665), and CCTA (0.607) (p > 0.05 for all) results. The addition of two FAI measures to the CCTA showed improvements in the discrimination (AUC) and reclassification ability (relative integrated discrimination improvement (IDI) and category-free net reclassification index (NRI)), vessel-specific FAI (AUC, 0.696; NRI, 49.6%; IDI, 5.9%), and lesion-specific FAI scores (AUC, 0.676; NRI, 43.3%; IDI, 5.4%); (p < 0.01 for all). Multivariate analysis revealed that low-attenuation plaque (LAP) volume was an independent predictor of two FAI measures. Conclusion: The combined approach of adding vessel-specific FAI or lesion-specific FAI scores could improve the identification of ischemia compared with CCTA alone. The LAP volume was the independent risk factor for both tools.

Keywords: coronary artery disease; coronary computed tomography angiography; fat attenuation index; ischemia.

Figure 1

Flowchart of patient’s selection. CCTA, coronary computed tomography angiography; FFR, fractional flow reserve.

Figure 2

Comparisons of vessel-specific FAI and lesion-specific FAI scores: (A) the distribution of vessel-specific FAI and lesion-specific FAI scores, with medians, quartiles, and ranges shown in the box plot; (B) the correlation between vessel-specific FAI and lesion-specific FAI scores, with the scatter diagram showing a positive correlation between them (R = 0.770, p < 0.001). FAI, fat attenuation index; HU, Hounsfield unit; NS, non-statistical significance.

Figure 3

Receiver operating characteristic curves for the CCTA, vessel-specific FAI, and lesion-specific FAI in predicting ischemia: (A) ROC curves for predicting ischemia using CCTA, vessel-specific FAI, and lesion-specific FAI. (B) ROC curves of models using CCTA with and without vessel-specific FAI and lesion-specific FAI, respectively. Cutoff values of −70.97 HU for vessel-specific FAI and −73.95 HU for lesion-specific FAI according to the Youden index were used for the comparison between CCTA with and without these scores. CCTA, coronary computed tomography angiography; FAI, fat attenuation index; ROC, receiver operating characteristic curves; HU, Hounsfield unit.

Figure 4

Example of a 42-year-old man with chest pain: (A) CCTA image showed a lesion analyzed with dedicated plaque analysis software proximal to the LAD with stenosis ranging between 70 and 90% (white arrow); (B,C) color-coded CPR image reveals that the mean perivascular FAIs of the lesion (lesion-specific FAI) and proximal 40 mm of LAD (vessel-specific FAI) were −63.75 HU and −67.92 HU, respectively; (D) measurement list shows the contents of various plaque components; (E) ICA showed that the stenosis degree of the lesion was about 90% (red arrow), and then FFR confirmed that the stenosis was hemodynamically significant (FFR = 0.75). CCTA, coronary computed tomography angiography; FAI, fat attenuation index; LAD, left anterior descending artery; CPR, curved planar reformation; HU, Hounsfield unit; ICA, invasive coronary angiography; FFR, fractional flow reserve.

Figure 5

Relationship between vessel-specific FAI, lesion-specific FAI, and stenosis based on CCTA: (A,B) distribution of vessel-specific FAI (A) and lesion-specific FAI (B) scores in each group with 30–49%, 50–69%, and 70–90% diameter stenosis on CCTA. Medians, quartiles, and ranges of vessel-specific FAI and lesion-specific FAI scores are shown in the box plot. Cutoff values of vessel-specific FAI and lesion-specific FAI scores are displayed as dashed lines. FAI, fat attenuation index; CCTA, coronary computed tomography angiography.

Figure 6

Distribution of vessel-specific FAI (A) and lesion-specific FAI (B) scores according to quartile of LAP volume (Q1–Q4). Values shown are medians (interquartile range). FAI, fat attenuation index; HU, Hounsfield unit; LAP, low-attenuation plaque.