Diffusion tensor imaging and arterial tissue: establishing the influence of arterial tissue microstructure on fractional anisotropy, mean diffusivity and tractography

Abstract

This study investigates diffusion tensor imaging (DTI) for providing microstructural insight into changes in arterial tissue by exploring how cell, collagen and elastin content effect fractional anisotropy (FA), mean diffusivity (MD) and tractography. Five ex vivo porcine carotid artery models (n = 6 each) were compared—native, fixed native, collagen degraded, elastin degraded and decellularised. Vessels were imaged at 7 T using a DTI protocol with b = 0 and 800 s/mm2 and 10 isotopically distributed directions. FA and MD were evaluated in the vessel media and compared across models. FA values measured in native (p < 0.0001), fixed native (p < 0.0001) and collagen degraded (p = 0.0018, p = 0.0016, respectively) were significantly higher than those in elastin degraded and decellularised arteries. Native and fixed native had significantly lower MD values than elastin degraded (p < 0.0001) and decellularised tissue (p = 0.0032, p = 0.0003, respectively). Significantly lower MD was measured in collagen degraded compared with the elastin degraded model (p = 0.0001). Tractography yielded helically arranged tracts for native and collagen degraded vessels only. FA, MD and tractography were found to be highly sensitive to changes in the microstructural composition of arterial tissue, specifically pointing to cell, not collagen, content as the dominant source of the measured anisotropy in the vessel wall.

Development of a Collagen Fibre Remodelling Rupture Risk Metric for Potentially Vulnerable Carotid Artery Atherosclerotic Plaques

“…This lack of remodelling to the optimum distribution could occur in diseased arteries due to a lack of cells present to produce fibres in the direction of the loads and/or possibly due to fibres being overly degraded (Gaul et al, 2018). This remodelling metric has the potential to be used as a pre-clinical indicator of the risk of atherosclerotic plaque rupture, particularly now that advancements in imaging modalities such as DTI show great promise in the in vivo characterisation of the structure of collagen fibres (Flamini et al, 2012;Akyildiz et al, 2017;Shahid et al, 2017;Tornifoglio et al, 2020).…”

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

“…For porcine and human vessels, Haematoxylin and Eosin (H&E), Picrosirius red, Verhoeff’s elastin and Alcian blue staining were performed to identify the presence of smooth muscle cells, collagen, elastin and glycosaminoglycans (GAGs) respectively 27 . Additionally, Alizarin Red staining was performed on human vessels to identify the presence of calcium.…”

Quantitative susceptibility mapping of carotid arterial tissue ex vivo: Assessing sensitivity to vessel microstructural composition

“…In this study, we hypothesize that the magnetic susceptibility of arterial vessels is sensitive to changes in the vessel wall microstructure. To test this, a high‐resolution QSM protocol was applied to excised porcine carotid arteries subjected to a range of enzymatic digestion treatments 27 . To relate the magnetic susceptibility of porcine tissue to human arterial tissue to accelerate potential clinical translation, the same QSM protocol was applied in ex vivo human carotid arteries.…”