title: Interrelations of muscle functional MRI, diffusion-weighted MRI and (31) P-MRS in exercised lower back muscles.
abstract: Exercise-induced changes of transverse proton relaxation time (T2 ), tissue perfusion and metabolic turnover were investigated in the lower back muscles of volunteers by applying muscle functional MRI (mfMRI) and diffusion-weighted imaging (DWI) before and after as well as dynamic (31) P-MRS during the exercise. Inner (M. multifidus, MF) and outer lower back muscles (M. erector spinae, ES) were examined in 14 healthy young men performing a sustained isometric trunk-extension. Significant phosphocreatine (PCr) depletions ranging from 30% (ES) to 34% (MF) and Pi accumulations between 95% (left ES) and 120%-140% (MF muscles and right ES) were observed during the exercise, which were accompanied by significantly decreased pH values in all muscles (∆pH ≈ -0.05). Baseline T2 values were similar across all investigated muscles (approximately 27 ms at 3 T), but revealed right-left asymmetric increases (T2 ,inc ) after the exercise (right ES/MF: T2 ,inc  = 11.8/9.7%; left ES/MF: T2 ,inc  = 4.6/8.9%). Analyzed muscles also showed load-induced increases in molecular diffusion D (p = .007) and perfusion fraction f (p = .002). The latter parameter was significantly higher in the MF than in the ES muscles both at rest and post exercise. Changes in PCr (p = .03), diffusion (p < .01) and perfusion (p = .03) were strongly associated with T2,inc , and linear mixed model analysis revealed that changes in PCr and perfusion both affect T2,inc (p < .001). These findings support previous assumptions that T2 changes are not only an intra-cellular phenomenon resulting from metabolic stress but are also affected by increased perfusion in loaded muscles.
authors: Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Center of Radiology, Jena University Hospital - Friedrich Schiller University, Jena, Germany.
authors: Patrick
authors: P
authors: Hiepe
authors: Alexander
authors: A
authors: Gussew
authors: Reinhard
authors: R
authors: Rzanny
authors: Christoph
authors: C
authors: Anders
authors: Mario
authors: M
authors: Walther
authors: Hans-Christoph
authors: HC
authors: Scholle
authors: Jürgen R
authors: JR
authors: Reichenbach
mesh_terms: D064131:Back Muscles / Q000502:physiology*; D038524:Diffusion Magnetic Resonance Imaging; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D010477:Perfusion; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes; D013997:Time Factors; D016474:Weight-Bearing; D055815:Young Adult
chemical_list: D010759:Phosphorus Isotopes; D010725:Phosphocreatine
keywords: MRS; T2 mapping; diffusion-weighted imaging; intra-voxel incoherent motion model; lower back; muscle; muscle functional MRI; phosphorus