Quantitative susceptibility mapping of carotid arterial tissueex vivo: assessing sensitivity to vessel microstructural composition

Abstract

Purpose: To characterise microstructural contributions to the magnetic susceptibility of carotid arteries. Method: Arterial vessels were scanned using high resolution quantitative susceptibility mapping (QSM) at 7T. Models of vessel degradation were generated using ex vivo porcine carotid arteries that were subjected to several different enzymatic digestion treatments that selectively removed microstructural components (smooth muscle cells, collagen and elastin). Magnetic susceptibilities measured in these tissue models were compared to those in untreated (native) porcine arteries. Magnetic susceptibility measured in native porcine carotid arteries was further compared to the susceptibility of cadaveric human carotid arteries to investigate their similarity. Results: The magnetic susceptibility of native porcine vessels was diamagnetic (χ native = -0.1820ppm), with higher susceptibilities in all models of vessel degradation (χ elastin degraded = -0.0163ppm; χ collagen degraded = -0.1158ppm; χ decellularised = -0.1379ppm; χ fixed native = -0.2199ppm). Magnetic susceptibility was significantly higher in collagen degraded compared to native porcine vessels (Tukey-Kramer, p<0.01) and between elastin degraded and all other models (including native, Tukey-Kramer, p<0.001). The susceptibility of fixed healthy human arterial tissue was diamagnetic and no significant difference was found between fixed human and fixed porcine arterial tissue susceptibilities (ANOVA, p>0.05). Conclusions: Magnetic susceptibility measured using QSM is sensitive to the microstructural composition of arterial vessels - most notably to collagen. The similarity of human and porcine arterial tissue susceptibility values provides a solid basis for translational studies. As vessel microstructure becomes disrupted during the onset and progression of carotid atherosclerosis, QSM has the potential to provide a sensitive and specific marker of vessel disease.