title: Dynamic 31P MR spectroscopy of plantar flexion: influence of ergometer design, magnetic field strength (3 and 7 T), and RF-coil design.
abstract: OBJECTIVE
  Dynamic phosphorus magnetic resonance spectroscopy ((31)P MRS) during and after acute exercise enables the noninvasive in vivo determination of the mitochondrial capacity of skeletal muscle. Nevertheless, the lack of standardization in experimental setups leads to significant variations in published values of maximal aerobic capacity, even in the population of healthy volunteers. Thus, in this study, we aimed to assess the impact of the ergometer type (pneumatic and mechanical resistance construction), radiofrequency (RF)-coil diameter, and different magnetic field strengths (3 and 7 T) on the metabolic parameters measured by dynamic (31)P MRS during a plantar flexion isotonic exercise protocol within the same group of healthy volunteers.
  
  
  METHODS
  Dynamic (31)P MRS measurements of the calf muscle in 11 volunteers (mean age, 36  ±  13 yrs; mean BMI, 23.5 ± 2.5 kg/m(2)), on a 3 T MR system with a custom-made mechanical ergometer in the first research laboratory (RL1) and on 3 and 7 T MR systems equipped with a commercial pneumatic ergometer in the second research laboratory (RL2), were performed at three different workloads. RF-coils differed slightly between the sites and MR systems used. The repeatability of the experimental protocol was tested in every setup. The basal concentrations of phosphocreatine (PCr), exercise-induced depletion of PCr (ΔPCr), initial PCr resynthesis rate (VPCr), and mitochondrial capacity (Qmax) were calculated and compared between the research sites and field strengths.
  
  
  RESULTS
  High repeatability of the measurement protocol was found in every experimental setup. No significant differences at any workload were found in these metabolic parameters assessed at different magnetic field strengths (3 T vs 7 T), using the same ergometer (in RL2) and a similar RF-coil. In the inter-research laboratory comparison at the same field strength (3 T), but with using different ergometers and RF-coils, differences were found in the concentration of PCr measured at rest and in the drop in PCr signal intensity. These differences translated into difference in the value of mitochondrial capacity at a workload of 15% of maximal voluntary contraction (MVC) force (0.45 ± 0.16 mM/s vs 0.31 ± 0.08 mM/s, in the RL1 and RL2, respectively).
  
  
  CONCLUSIONS
  Metabolic parameters measured during exercise challenge by dynamic (31)P MRS do not depend upon the magnetic field strength used. For multicenter studies with different ergometers, it is important to set the same workload, measurement, and evaluation protocols, especially when the effects of very mild exercise (15% MVC) are to be compared. However, a higher workload (24% MVC) decreases the influence of imperfections and intersite differences for the assessed value of maximal mitochondrial capacity.
authors.affiliation: MR-Unit, Department of Diagnostic and Interventional Radiology, Institute for Clinical and Experimental Medicine, Prague 140 21, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Šedivý
authors.affiliation: High-Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna A-1090, Austria and Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna A-1090, Austria.
authors.forename: Monika Christina
authors.initials: MC
authors.lastname: Kipfelsberger
authors.affiliation: MR-Unit, Department of Diagnostic and Interventional Radiology, Institute for Clinical and Experimental Medicine, Prague 140 21, Czech Republic.
authors.forename: Monika
authors.initials: M
authors.lastname: Dezortová
authors.affiliation: High-Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna A-1090, Austria; Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Vienna A-1090, Austria; and Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna A-1090, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Krššák
authors.affiliation: MR-Unit, Department of Diagnostic and Interventional Radiology, Institute for Clinical and Experimental Medicine, Prague 140 21, Czech Republic.
authors.forename: Miloslav
authors.initials: M
authors.lastname: Drobný
authors.affiliation: High-Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna A-1090, Austria and Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna A-1090, Austria.
authors.forename: Marek
authors.initials: M
authors.lastname: Chmelík
authors.affiliation: MR-Unit, Department of Diagnostic and Interventional Radiology, Institute for Clinical and Experimental Medicine, Prague 140 21, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Rydlo
authors.affiliation: High-Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna A-1090, Austria and Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna A-1090, Austria.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Trattnig
authors.affiliation: MR-Unit, Department of Diagnostic and Interventional Radiology, Institute for Clinical and Experimental Medicine, Prague 140 21, Czech Republic.
authors.forename: Milan
authors.initials: M
authors.lastname: Hájek
authors.affiliation: High-Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna A-1090, Austria; Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Bratislava 841 04, Slovakia; and Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna A-1090, Austria.
authors.forename: Ladislav
authors.initials: L
authors.lastname: Valkovič
mesh_terms: D000328:Adult; D004867:Equipment Design; D016552:Ergometry / Q000295:instrumentation* / Q000379:methods; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D007551:Isotonic Contraction / Q000502:physiology*; D007866:Leg / Q000502:physiology*; D060526:Magnetic Fields; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods*; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes; D015203:Reproducibility of Results
chemical_list: D010759:Phosphorus Isotopes; D010725:Phosphocreatine