Dynamic phosphocreatine imaging with unlocalized pH assessment of the human lower leg muscle following exercise at 3T

• Published in: Magnetic resonance in medicine 2018-02, Vol.79 (2), p.974-980
• Main Authors: Khegai, Oleksandr, Madelin, Guillaume, Brown, Ryan, Parasoglou, Prodromos
• Format: Article
• Language: English
• Subjects: Adult; Contraction; Data acquisition; dynamic 31P MRI; Exercise - physiology; Gastrocnemius muscle; human calf muscle; Humans; Hydrogen ions; Hydrogen-Ion Concentration; Image processing; Image segmentation; Imaging, Three-Dimensional - methods; Kinetics; Leg; Localization; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; muscle metabolism; Muscle, Skeletal - diagnostic imaging; Muscle, Skeletal - physiology; Muscles; pH assessment; pH effects; Phosphates; Phosphocreatine; Phosphocreatine - analysis; Phosphocreatine - chemistry; Phosphocreatine - metabolism; phosphocreatine resynthesis; Phosphorus; Phosphorus Isotopes; Plantar flexion; Temporal resolution; Time constant; X‐nuclei imaging; Young Adult
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.26728

Purpose To develop a high temporal resolution imaging method that measures muscle‐specific phosphocreatine (PCr) resynthesis time constant (τPCr) and pH changes in muscles of the lower leg following exercise on a clinical 3T MRI scanner. Methods We developed a frequency‐selective 3D non‐Cartesian FLORET sequence to measure PCr with 17‐mm nominal isotropic resolution (28 mm actual resolution) and 6‐s temporal resolution to capture dynamic metabolic muscle activity. The sequence was designed to additionally collect inorganic phosphate spectra for pH quantification, which were localized using sensitivity profiles of individual coil elements. Nineteen healthy volunteers were scanned while performing a plantar flexion exercise on an in‐house developed ergometer. Data were acquired with a dual‐tuned multichannel coil array that enabled phosphorus imaging and proton localization for muscle segmentation. Results After a 90‐s plantar flexion exercise at 0.66 Hz with resistance set to 40% of the maximum voluntary contraction, τPCr was estimated at 22.9 ± 8.8 s (mean ± standard deviation) with statistical coefficient of determination r2 = 0.89 ± 0.05. The corresponding pH values after exercise were in the range of 6.9‐7.1 in the gastrocnemius muscle. Conclusion The developed technique allows measurement of muscle‐specific PCr resynthesis kinetics and pH changes following exercise, with a temporal resolution and accuracy comparable to that of single voxel 31P‐MRS sequences. Magn Reson Med 79:974–980, 2018. © 2017 International Society for Magnetic Resonance in Medicine.