Microvasculature alters the dispersion properties of shear waves - a multi-frequency MR elastography study

• Published in: NMR in biomedicine Vol. 28; no. 12; pp. 1763 - 1771
• Main Authors: Jugé, Lauriane, Petiet, Anne, Lambert, Simon A., Nicole, Pascal, Chatelin, Simon, Vilgrain, Valerie, Van Beers, Bernard E., Bilston, Lynne E., Sinkus, Ralph
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.12.2015; Wiley Subscription Services, Inc; Wiley
• Subjects: Animals; Aorta - anatomy & histology; Aorta - physiology; aortic ring model; Biomechanics; Computer Science; Coronary vessels; Elasticity Imaging Techniques - methods; Image Interpretation, Computer-Assisted - methods; In Vitro Techniques; Magnetic Fields; Male; Mechanics; Medical Imaging; Microvessels - anatomy & histology; Microvessels - physiology; MR elastography (MRE); Physics; Rats; Rats, Inbred F344; Reproducibility of Results; Scattering, Radiation; Sensitivity and Specificity; Shear Strength - physiology; shear wave speed (cs); structural imaging biomarkers; viscoelasticity; MR elastography (MRE); shear wave speed (cs); structural imaging biomarkers; viscoelasticity; aortic ring model
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.3438

Magnetic Resonance Elastography (MRE) uses macroscopic shear wave propagation to quantify mechanical properties of soft tissues. Micro‐obstacles are capable of affecting the macroscopic dispersion properties of shear waves. Since disease or therapy can change the mechanical integrity and organization of vascular structures, MRE should be able to sense these changes if blood vessels represent a source for wave scattering. To verify this, MRE was performed to quantify alteration of the shear wave speed cs due to the presence of vascular outgrowths using an aortic ring model. Eighteen fragments of rat aorta included in a Matrigel matrix (n=6 without outgrowths, n=6 with a radial outgrowth extent of ~600µm and n=6 with ~850µm) were imaged using a 7 Tesla MR scanner (Bruker, PharmaScan). High resolution anatomical images were acquired in addition to multi‐frequency MRE (ν = 100, 115, 125, 135 and 150 Hz). Average cs was measured within a ring of ~900µm thickness encompassing the aorta and were normalized to cs0 of the corresponding Matrigel. The frequency dependence was fit to the power law model cs ~νy. After scanning, optical microscopy was performed to visualize outgrowths. Results demonstrated that in presence of vascular outgrowths (1) normalized cs significantly increased for the three highest frequencies (Kruskal‐Wallis test, P = 0.0002 at 125 Hz and P = 0.002 at 135 Hz and P = 0.003 at 150 Hz) but not for the two lowest (Kruskal‐Wallis test, P = 0.63 at 100 Hz and P = 0.87 at 115 Hz), and (2) normalized cs followed a power law behavior not seen in absence of vascular outgrowths (ANOVA test, P < 0.0001). These results showed that vascular outgrowths acted as micro‐obstacles altering the dispersion relationships of propagating shear waves and that MRE could provide valuable information about microvascular changes. Copyright © 2015 John Wiley & Sons, Ltd. Mechanical properties, as assessed by MR elastography (MRE), could be biomarkers for microvasculature changes if blood vessels represent a source of wave scattering. To verify this, MRE was performed to quantify the alterations in the shear wave speed cs caused by the presence of vascular outgrowths using a rat aortic ring model. The results showed that, in the presence of vascular outgrowths relative to plain Matrigel, cs increased and followed a frequency power law not seen in the absence of vascular outgrowths.