Photon counting spectral CT component analysis of coronary artery atherosclerotic plaque samples

Abstract

Objective: To evaluate the capabilities of photon counting spectral CT to differentiate components of coronary atherosclerotic plaque based on differences in spectral attenuation and iodine-based contrast agent concentration. Methods: 10 calcified and 13 lipid-rich non-calcified histologically demonstrated atheromatous plaques from post-mortem human coronary arteries were scanned with a photon counting spectral CT scanner. Individual photons were counted and classified in one of six energy bins from 25 to 70 keV. Based on a maximum likelihood approach, maps of photoelectric absorption (PA), Compton scattering (CS) and iodine concentration (IC) were reconstructed. Intensity measurements were performed on each map in the vessel wall, the surrounding perivascular fat and the lipid-rich and the calcified plaques. PA and CS values are expressed relative to pure water values. A comparison between these different elements was performed using Kruskal-Wallis tests with pairwise post hoc Mann-Whitney U-tests and Sidak p-value adjustments. Results: Results for vessel wall, surrounding perivascular fat and lipid-rich and calcified plaques were, respectively, 1.19 6 0.09, 0.73 6 0.05, 1.08 6 0.14 and 17.79 6 6.70 for PA; 0.96 6 0.02, 0.83 6 0.02, 0.91 6 0.03 and 2.53 6 0.63 for CS; and 83.3 6 10.1, 37.6 6 8.1, 55.2 6 14.0 and 4.9 6 20.0 mmol l 21 for IC, with a significant difference between all tissues for PA, CS and IC (p , 0.012).Conclusion: This study demonstrates the capability of energy-sensitive photon counting spectral CT to differentiate between calcifications and iodine-infused regions of human coronary artery atherosclerotic plaque samples by analysing differences in spectral attenuation and iodine-based contrast agent concentration. Advances in knowledge: Photon counting spectral CT is a promising technique to identify plaque components by analysing differences in iodine-based contrast agent concentration, photoelectric attenuation and Compton scattering.The role of atherosclerotic plaque rupture in acute coronary events is well established. 1 Plaques prone to rupture display a large lipid-rich core, a thin fibrous cap and an inflammatory infiltration.2 CT is now considered as a reliable tool to assess coronary artery stenosis, 3 but still has two main shortcomings. Firstly, differentiating between intraluminal iodinebased contrast agent and plaque calcification remains challenging in small vessels such as the coronary arteries, leading to an erroneous estimation of the degree of stenosis. Secondly, CT is limited in correctly identifying plaque components, especially for the detection of the lipid core out of the normal wall or the fibrous plaque components.4-8 These problems are related to the insufficient spatial resolution available with the current clinical system and to the overlaps of the Hounsfield values between iodine and calcifications on one hand and the lipid core and other soft components of the arterial wall on the other hand. Improved differentiation between calcification and iodine was obtained wi...

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