Cardiac CT Perfusion Imaging of Pericoronary Adipose Tissue (PCAT) Highlighting Potential Confounds in CTA Analysis

Figure 1. Pipeline of PCAT analysis in CCTP data. See text for description.

Figure 2. HU time courses in ROIs of a patient with unobstructed coronary arteries and adequate myocardial perfusion. Color-coded plots in (b) correspond to the ROIs identified in (a) bottom. In (a) top, HU values are shown in PCAT around the LAD at different scan times. HUs are elevated at scans 7 and 11 compared to scan 1. There are 11 scans comprising ~22 s in a shuttle mode acquisition. The vertical dashed line shows the scan of peak enhancement in the aorta, which we deem the CCTA imaging time point, Pa. EAT = epicardial adipose tissue; HU = Hounsfield unit; MYO = myocardium; PAAT = periaortic adipose tissue; PAT = paracardial adipose tissue; PCAT = pericoronary adipose tissue; ROI = region of interest; SUB = subcutaneous adipose tissue.

Figure 3. Comparison of PCAT enhancement to LAD and the nearby myocardium. CCTP image shows iodine in PCAT of LAD and myocardium (a). (See Supplementary Material Video S1 for dynamic iodine enhancement.) Curved-planar-reformatted images of LAD for scans 1, 5, and 9 are shown in (b), (c) and (d), respectively. Note the enhancement in the middle scan. Enhancement time courses of LAD, PCAT, and the nearby myocardium are remarkably similar in (e), (f), and (g), respectively. We computed the blood flow of myocardial and PCAT around LAD in (h) using our software described in Methods. Abbreviations are described in Figure 1.

Figure 4. HUs of adipose ROIs at different times. HUs at the first scan (P1) vary greatly between ROIs, with the lowest value in pericardial adipose (PAT) and the highest in periaortic adipose (PAAT). Other times are relative to the time of peak enhancement of the aorta (Pa). Epicardial adipose tissue (EAT) changes more than other ROIs. Abbreviations are the same as in Figure 1.

Figure 5. HU changes relative to baseline (P1) for various adipose depots and time points across 9 patients. ΔHU value order, PCAT > EAT > PAT ≥ SUB. PCAT is similar in LAD and RCA. Maximum enhancement (at PPCAT) is significantly different from Pa, suggesting an enhancement delay in some hearts. Average time for PPCAT is Pa+2. Only vessels without obstructive disease are used (6 LADs and 6 RCAs). * p < 0.05. Abbreviations are described in Figure 1.

Figure 6. Regional HU values within EAT (containing PCAT and remote EAT). EAT and remote EAT ROIs are shown in (a) and (b), respectively. Baseline HU and changes with enhancement vary across ROIs, with PCAT changing the most (c). Only vessels without obstructive disease are used (6 LADs and 6 RCAs). Abbreviations are described in Figure 1.

Figure 7. HU value of adipose as a function of radial distance from the vessel wall. The three non-overlapping ROIs are shown in (a). The diameter of blue, white, and green circles are 2 × D, 3 × D, and 4 × D, where D is the diameter of the vessel wall. HU values at different times for the different ROIs are shown in (b). Baseline HU is higher near the vessel wall. The enhancement change in HU increases near the vessel wall. Only vessels without obstructive disease are computed (6 LADs and 6 RCAs). Please note that the white circle (3 × D) roughly corresponds to the region of interest reported in the literature. Clearly, the 2 × D disk gives higher HU values than the 3 × D annular ring, indicating a spatial gradient from the vessel wall. In all regions, there is a dependence upon the frame since the time of injection. To determine if there was a time dependence of the spatial gradient, we analyzed the change (ΔHU) between average HUs in the 2 × D disk and the 3 × D annular ring as a function of the image frame. The ΔHU values were 3.7 ± 4.7, 3.6 ± 4.5, 4.4 ± 4.8, 6.8 ± 5.1, and 8.3 ± 5.1 HU for frames P1, Pa−1, Pa, Pa+1, and PPCAT, respectively, again suggesting a dependence upon…

Figure 8. HU time courses in ROIs of a patient with an obstructive lesion and reduced myocardial blood flow in the RCA territory. Severe stenosis on the RCA (a) corresponds to reduced proximal myocardial blood flow. (b) Distal as compared to proximal PCAT ROIs [blue and brown regions in (a)] give a delayed and depressed enhancement time course (c-bottom), which is reasonably mirrored in the myocardial regions. Perfusion pressure proximal to the lesion will be increased relative to that found distally. Myo: myocardium.

Figure 9. PCAT apparent volume changes over time. In (a), LAD PCAT apparent volume change (bottom) is shown for the patient (above) with non-obstructive disease and a fat threshold [−190 HU, −30 HU]. In (b), the percentage of apparent volume change relative to P1 is shown across all vessels with the conventional threshold and an adjusted threshold [−190 HU, −10 HU]. The solid line is the mean, and the shadow is the standard error. Percent apparent volume changes are substantial but reduced with the adjusted threshold.

Figure 10. Changes in feature values with iodine perfusion. Twenty-one hand-crafted and radiomic library features are on the vertical axis. We present mean percent changes as compared to values at P1 from Pa−4 to Pa+4. The range of change was [−214%, 460%], but data were truncated to [−30%, 30%] for visualization. We analyzed vessel territories without an obstruction (n = 12).