Advanced diffusion MRI for skeletal muscle applications

Skeletal muscles play a key role in maintaining mobility and functional independence. Impairments of muscles due to injury or disease can severely impact the quality of life. Magnetic resonance imaging (MRI) plays a crucial role in diagnosing and monitoring skeletal muscle pathologies. Diffusion MRI provides valuable insights into microstructural changes and is sensitive to pathological alterations in muscle tissue. This thesis aimed to advance the application of diffusion MRI techniques and optimize their sensitivity for skeletal muscle pathologies. The main focus was on enhancing diffusion tensor imaging (DTI) to accurately characterize muscle fiber integrity and intravoxel incoherent motion (IVIM) to separate diffusion and perfusion effects within muscle tissue, with the goal of improving the detection and quantification of muscle pathologies.
Chapter 2 demonstrated that IVIM-corrected DTI can be accelerated to less than 4 minutes without affecting the parameter sensitivity to muscle injury in a study on 109 athletes with acute hamstring injury. Longer diffusion times did not improve the detection of subtle microstructural changes in marathon runners (Chapter 3). However, using multiple diffusion times enables sophisticated diffusion modeling to estimate muscle fiber size and permeability non-invasively. Moving from muscle injuries to neuromuscular diseases, a multi-parametric MRI approach containing fat fraction, water T2, water T1, pH measure, and DTI at four diffusion times was applied in a longitudinal study of limb-girdle muscular dystrophy R9 patients in Chapter 4. Model-based reconstructions (Chapter 5) and hardware improvements (Chapter 6) might allow further acceleration, as demonstrated in healthy volunteers in this thesis.