title: Exercising calf muscle T₂∗ changes correlate with pH, PCr recovery and maximum oxidative phosphorylation.
abstract: Skeletal muscle metabolism is impaired in disorders like diabetes mellitus or peripheral vascular disease. The skeletal muscle echo planar imaging (EPI) signal (S(EPI) ) and its relation to energy metabolism are still debated. Localised ³¹P MRS and S(EPI) data from gastrocnemius medialis of 19 healthy subjects were combined in one scanning session to study direct relationships between phosphocreatine (PCr), pH kinetics and parameters of T₂∗ time courses. Dynamic spectroscopy (semi-LASER) and EPI were performed immediately before, during and after 5 min of plantar flexions. Data were acquired in a 7 T MR scanner equipped with a custom-built ergometer and a dedicated ³¹P/¹H radio frequency (RF) coil array. Using a form-fitted multi-channel ³¹P/¹H coil array resulted in high signal-to-noise ratio (SNR). PCr and pH in the gastrocnemius medialis muscle were quantified from each ³¹P spectrum, acquired every 6 s. During exercise, SEPI (t) was found to be a linear function of tissue pH(t) (cross-correlation r = -0.85 ± 0.07). Strong Pearson's correlations were observed between post exercise time-to-peak (TTP) of SEPI and (a) the time constant of PCr recovery τPCr recovery (r = 0.89, p < 10⁻⁶), (b) maximum oxidative phosphorylation using the linear model, Q(max, lin) (r = 0.65, p = 0.002), the adenosine-diphosphate-driven model, Q(max,ADP) (r = 0.73, p = 0.0002) and (c) end exercise pH (r = 0.60, p = 0.005). Based on combined accurately localised ³¹P MRS and T₂∗ weighted MRI, both with high temporal resolution, strong correlations of the skeletal muscle SEPI during exercise and tissue pH time courses and of post exercise SEPI and parameters of energy metabolism were observed. In conclusion, a tight coupling between skeletal muscle metabolic activity and tissue T₂∗ signal weighting, probably induced by osmotically driven water shift, exists and can be measured non-invasively, using NMR at 7 T.
authors.affiliation: Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Wien, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasee 14, 1090, Wien, Austria.
authors.forename: Albrecht Ingo
authors.initials: AI
authors.lastname: Schmid
authors.forename: Kiril
authors.initials: K
authors.lastname: Schewzow
authors.forename: Georg Bernd
authors.initials: GB
authors.lastname: Fiedler
authors.forename: Sigrun
authors.initials: S
authors.lastname: Goluch
authors.forename: Elmar
authors.initials: E
authors.lastname: Laistler
authors.forename: Michael
authors.initials: M
authors.lastname: Wolzt
authors.forename: Ewald
authors.initials: E
authors.lastname: Moser
authors.forename: Martin
authors.initials: M
authors.lastname: Meyerspeer
mesh_terms: D000328:Adult; D003710:Demography; D017352:Echo-Planar Imaging; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007866:Leg / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010085:Oxidative Phosphorylation; D010725:Phosphocreatine / Q000031:analogs & derivatives / Q000378:metabolism*; D013997:Time Factors; D055815:Young Adult
chemical_list: D010725:Phosphocreatine; C025403:phosphocreatinine
keywords: 31P MRS; 7 Tesla; T*2; energy metabolism; exercise; pH; plantar flexion; skeletal muscle