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

In this study we investigated the potential of diffusion tensor imaging (DTI) for providing insight into microstructural changes in arterial tissue by exploring the influence that cell, collagen and elastin content have on fractional anisotropy (FA), mean diffusivity (MD) and tractography. Five ex vivo porcine carotid artery models (n = 6 vessels each) - native, fixed native, collagen degraded, elastin degraded and decellularised - were developed to selectively remove components of arterial microstructure. Intact 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 values were evaluated in the medial layer of vessels and compared across tissue models. FA values measured in native and fixed native vessels were significantly higher (p<0.0001) than those in the elastin degraded and decellularised arteries. Collagen degraded vessels had a significantly higher (p<0.01) FA than elastin degraded and decellularised vessels. Native and fixed vessels had significantly lower (p<0.0001) MD values than elastin degraded, while the MD in decellularised arteries was significantly higher than that in both native (p<0.01) and fixed (p<0.005) tissue. Significantly lower (p<0.005) MD was measured in collagen degraded compared with the elastin degraded model. Tractography results yielded similar helically arranged tracts for native and collagen degraded vessels, whilst elastin degraded and decellularised vessels showed no consistent tracts. FA, MD and tractography were found to be highly sensitive to changes in the microstructural composition of arterial tissue, with cell content being a dominant source of the measured anisotropy in the vessel wall.