VisR ultrasound evaluation of dystrophic muscle degeneration in a dog cross-section and comparison to histology and MRI

Viscoelastic Response (VisR) ultrasound is a new Acoustic Radiation Force (ARF)-based imaging method that uses two successive ARF excitations, delivered to the same region of excitation, to approximate a creep response in tissue and thereby estimate viscoelastic property. The viscoelasticity of dystrophic muscle is altered over time by ongoing necrotic, fatty, and fibrous degenerative changes. Evaluating such changes by VisR in the Golden Retriever Muscular Dystrophy (GRMD) canine model, with comparison to matched MRI and histology, is the purpose of this work. In a cross-sectional study, in vivo VisR imaging was performed on the vastus lateralis (VL) and cranial sartorius (CS) muscles in 20 dogs (n=10 control and GRMD age-matched pairs) aged 3, 6, 12, 24, or 60 months. Following VisR, T2-weighted MRI imaging was performed, and run percentage (RP) was calculated to reflect heterogeneity. Finally, muscle tissue samples were acquired by open surgical biopsy, sectioned, and stained, and percent collagen and fat were calculated from digital microscopy. In the VL, SD of VisR τ was consistently larger in GRMD versus age-matched control dogs (p=0.001, Wilcoxon two-sample test). This VisR result was consistent with higher MRI RP measures and higher histology percent collagen. Similarly in the CS, SD of VisR τ was larger in GRMD than control (p=0.001), consistent with higher MRI RP and with histology percent collagen. These results suggest that VisR measures of τ SD reflect heterogeneity due to collagen deposition in dystrophic muscles.