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Open Access Thesis

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Master of Science (M.S.)

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INTRODUCTION: The detection of a second inorganic phosphate (Pi) resonance, a possible marker of mitochondrial content in vivo, using phosphorus magnetic resonance spectroscopy (31P- MRS) at 3T is technically challenging, which may prevent its reproducible quantification. PURPOSE: To determine the reproducibility of resting alkaline inorganic phosphate (Pialk) measurement using 31P-MRS in human skeletal muscle at 3 tesla (T). METHODS: Resting 31P- MRS of the quadriceps muscles was acquired on two separate visits, within seven days, in 13 healthy, sedentary to moderately active young adults using a whole-body 3T MR system. Measurement variability related to coil position, shimming procedure, and spectral analysis were also quantified. 31P-MRS data were acquired with a 31P/1H dual-tuned surface coil positioned on the quadriceps using a pulse-acquire sequence. Test-retest absolute and relative reproducibility were analyzed using coefficient of variation (CV) and intra-class correlation coefficients (ICC), respectively. RESULTS: Pialk demonstrated a within-subject reproducibility marginally greater then the 10% cutoff (CV: 10.6 ± 5.4%; ICC: 0.80), but still appropriate given its small concentration in relation to other 31P metabolites. Proximo-distal change in coil positioning along the length of the quadriceps induced large variability in Pialk quantification (CV: 21.1%). In contrast, measurement variability due to repeated shims on consecutive scans from the same muscle sample (CV: 6.6%), and the automated spectral processing procedure, were minor (CV: 2.3%). Both metrics of absolute and relative reproducibility of Pialk were of similar magnitude to other well-resolved metabolites (e.g., phosphocreatine, Pi, and phosphodiester). CONCLUSION: Using multiple metrics, the present study established the high reproducibility of Pialk quantification by 31P-MRS using a surface coil on the quadriceps muscle at 3T. However, large variability in Pialk quantification can originate from positioning the coil on the most distal part of the quadriceps, which should be avoided due to shimming inhomogeneity.


First Advisor

Gwenael Layec