¹H and ³¹P MRS Interleaved With High Time Resolution Reveals Closely Matching Creatine CH₂ and PCr Dynamics During...

Area of Science:

• Biomedical Engineering
• Metabolic Physiology
• Magnetic Resonance Imaging

Background:

• Phosphocreatine (PCr) kinetics, measured via 31P Magnetic Resonance Spectroscopy (MRS), are established indicators of muscle oxidative capacity.
• Creatine's CH2 resonance in 1H MRS exhibits similar patterns, but direct comparisons with PCr have been limited by experimental constraints.

Purpose of the Study:

• To directly compare the kinetics of creatine-CH2 (1H MRS) and PCr (31P MRS) within a single, time-resolved experiment.
• To assess the extent to which creatine-CH2 dynamics reflect PCr dynamics during exercise and recovery.
• To investigate the visibility and utility of myocellular creatine measurements using 1H MRS.

Main Methods:

• Twenty-seven volunteers (lower and higher BMI groups) underwent interleaved 1H and 31P MRS during a 5-minute submaximal exercise and recovery protocol on a 7T MR system.
• Data were acquired with a 6-second time resolution, enabling direct kinetic analysis of both PCr and creatine-CH2.
• Kinetic time constants for exercise and recovery were calculated and compared between the two MRS methods and between BMI groups.

Main Results:

• Exercise induced a decrease in the creatine-CH2 signal, while the CH3 resonance remained stable.
• No significant differences were found in the time constants for recovery or exercise-on kinetics between 1H (creatine-CH2) and 31P (PCr) MRS within each BMI group.
• Significantly different time constants were observed between lower and higher BMI groups for both MRS methods, indicating distinct metabolic responses.
• A strong positive correlation was observed between creatine-CH2 and PCr depletion kinetics.

Conclusions:

• Creatine-CH2 kinetics measured by 1H MRS closely match PCr kinetics measured by 31P MRS in a single time-resolved experiment.
• The strong correlation and preserved intergroup differences suggest that 1H MRS quantification of creatine-CH2 can serve as a surrogate for estimating oxidative capacity via PCr from 31P MRS.
• These findings support the use of 1H MRS for assessing myocellular creatine pools and their dynamics, potentially offering a more accessible method than 31P MRS.