Feasibility of measuring pericoronary fat from precontrast scans: Effect of iodinated contrast on pericoronary fat attenuation

Background: Pericoronary adipose tissue (PCAT) attenuation has been identified as a marker for cardiovascular risk. The effect of contrast enhancement on fat attenuation is unknown. We aim to compare precontrast coronary scans to postcontrast CCTA for quantification of pericoronary fat volume and attenuation. Methods: Thin slice preand post-contrast studies obtained at 120 kVp, heart rate < 60, with no plaque or artifact in the right coronary artery (RCA) were selected. Analysis was limited to pixels -30 Hounsfield units (HU) to -190 HU and from 10 mm to 50 mm distal to the RCA origin at a radial distance equal to the vessel diameter. subgroup with no plaque across all coronaries was also analyzed. Results: Of 119 study pairs, the average RCA diameter was highly correlated at 3.85 mm (postcontrast) and 3.84 mm (precontrast), r = 0.97, p < 0.0001. The mean attenuation of preand postcontrast images was also highly correlated at -87.02 +/- 7.15 HU and -82.74 +/- 6.54 HU, respectively (r = 0.65, p < 0.0001). Pericoronary fat volume in the -190 to -30 HU range was 396 mm3 lower in the post contrast versus pre contrast, consistent with higher attenuation (less negative) voxels postcontrast (p < 0.0001). Interand intrareader agreement ranged 95-100% and 90% for precontrast and 85-90% for postcontrast studies, respectively. Subgroup analysis revealed precontrast attenuation -85.59 +/- 7.53 HU and postcontrast -82.21 +/- 7.15 HU were highly correlated r = 0.67, p < 0.0001. Conclusion: Pericoronary fat enhances with iodinated contrast, potentially explaining some of its risk-predictive capabilities. Fat attenuation and volume can be reliably measured from precontrast calcium scans, with volume quantification showing particularly strong correlation. Excellent interand intra-reader agreement is also demonstrated.