Viscoelastic Strain Response (ViSR) ultrasound assessment of viscoelastic properties in human duchenne muscular dystrophy, in vivo

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder that is caused by a mutation in the gene for dystrophin leading to a loss of the dystrophin protein from the muscle cell (myofiber) membrane. Viscoelastic Strain Response (ViSR) ultrasound is a new, quantitative acoustic radiation force (ARF) based elastographic imaging method to calculate τ, the viscoelastic relaxation time constant for constant stress. We have investigated the use of ViSR imaging in human DMD. Imaging was performed in vivo on the right rectus femoris (RF), sartorius (SART), and gastrocnemius (GAST) muscles of two boys with DMD. The boys were 5-and 9-years-old at the time of imaging. ViSR results in the 5-year-old showed an average of 27.0%, 6.6%, and 18.2% fat/necrosis composition in the RF, SART, and GAST, respectively. In the 9-year old subject, ViSR showed an average fat/necrosis composition of 66.7% in the RF, 9.1% in the SART, and 37.2% in the GAST. These results are consistent with both the known phenotypic response of the three muscles and with functional testing results and point to ViSR's potential relevance as a novel outcome measure for diagnostics and clinical trials in DMD.