Figure 4
Schematic model of changes in GAG content and structure and its measurements with bi-exponential T1ρ. (a) shows a cross-section of the molecular environment in normal skeletal muscle. T1ρ measures the chemical exchange between negatively charged GAG and protons in water. In (b), excessive GAG in stiff muscles undergoes a phase change, forming aggregates and trapping water in macromolecular spheres. The relative fraction of the short component increases due to GAG accumulation. T1ρs is relatively unchanged as the chemical exchange is unchanged, but T1ρl increases due to the trapped free water. In (c), treatment with hyaluronidase breaks down the GAG aggregates/ macromolecular spheres, with a shift in T1ρ parameters to more normal values.
