Exploring arterial tissue microstructural organization using non-Gaussian diffusion magnetic resonance schemes

Abstract

The purpose of this study was to characterize the alterations in microstructural organization of arterial tissue using higher-order diffusion magnetic resonance schemes. Three porcine carotid artery models namely; native, collagenase treated and decellularized, were used to estimate the contribution of collagen and smooth muscle cells (SMC) on diffusion signal attenuation using gaussian and non-gaussian schemes. The samples were imaged in a 7 T preclinical scanner. High spatial and angular resolution diffusion weighted images (DWIs) were acquired using two multi-shell (max b-value = 3000 s/mm2) acquisition protocols. The processed DWIs were fitted using monoexponential, stretched-exponential, kurtosis and bi-exponential schemes. Directionally variant and invariant microstructural parametric maps of the three artery models were obtained from the diffusion schemes. The parametric maps were used to assess the sensitivity of each diffusion scheme to collagen and SMC composition in arterial microstructural environment. The inter-model comparison showed significant differences across the considered models. The bi-exponential scheme based slow diffusion compartment (Ds) was highest in the absence of collagen, compared to native and decellularized microenvironments. In intra-model comparison, kurtosis along the radial direction was the highest. Overall, the results of this study demonstrate the efficacy of higher order dMRI schemes in mapping constituent specific alterations in arterial microstructure.

Ex Vivo Study Using Diffusion Tensor Imaging to Identify Biomarkers of Atherosclerotic Disease in Human Cadaveric Carotid Arteries

“…The FA is significantly lower in these aged samples than in previous studies investigating healthy porcine arterial tissue. 25–27 No subjects in this study died of cardiovascular disease; however, there were varying signs of atherosclerosis present for all subjects. While it is not possible to know for sure these subjects were asymptomatic, the signs of advanced disease present in most subjects combined with noncardiovascular-related CODs suggests it was in fact the silent progression of atherosclerosis.…”

“…Additionally, the extreme scan times in this study are not clinically feasible; however, other studies have identified different DTI acquisition techniques which speed up acquisition. 26 , 27 , 29 While there is still work to be done on the clinical translation of this work, the authors think this study highlights the potential of this imaging technique for clinical use. Future work will focus on bringing this imaging method to more clinically relevant fresh tissue.…”

Exploring DTI-derived metrics to non-invasively track recellularisation in vascular tissue engineering

“…This relationship is further confirmed by the strong correlation between FA and cell density. While the mono-exponential DTI model has shown that the main contributor to the measurable anisotropic diffusion in arterial tissue is cellular content 52 , non-gaussian schemes, such as the stretched-exponential model, have been used to further hone in on alterations in the tissue microstructure 53 .…”

“…Chemical exchange saturation transfer has shown an ability to measure specific concentrations of different molecules 69,70 ; however, its use in tissue engineering is limited 71 . DTI has been used in a handful of focused studies in different tissues to understand how different microstructural components affect the measurable signal 52,53,72 . A significant benefit to DTI is the ability to get directional information about the underlying microstructurea feature which is highly relevant in both cardiac 19,[73][74][75] and cartilaginous [76][77][78] tissues.…”

“…The aim of this study was to evaluate recellularisation in vascular grafts, specifically decellularised porcine carotids, over a two-week culture period using just one MRI technique -DTI. Having previously been shown to be sensitive to specific changes in arterial microstructure 52,53 , the DTI results presented in this work are explained and validated by quantitative histological analysis. This work shows that both qualitative and quantitative DTI-derived metrics are not only sensitive to changes in microstructure in TEVG, but strongly correlate with the recellularisation of these grafts.…”