Abstract
Magnetic resonance imaging (MRI) is extensively used in clinical and basic biomedical research. However, MRI detection of pH changes still poses a technical challenge. Chemical exchange saturation transfer (CEST) imaging is a possible solution to this problem. Using saturation transfer, alterations in the exchange rates between the solute and water protons because of small pH changes can be detected with greater sensitivity. In this study, we examined a fatigued skeletal muscle model in electrically stimulated mice. The measured CEST signal ratio was between 1.96 ppm and 2.6 ppm in the z-spectrum, and this was associated with pH values based on the ratio between the creatine (Cr) and the phosphocreatine (PCr). The CEST results demonstrated a significant contrast change at the electrical stimulation site. Moreover, the pH value was observed to decrease from 7.23 to 7.15 within 20 h after electrical stimulation. This pH decrease was verified by 31P magnetic resonance spectroscopy and behavioral tests, which showed a consistent variation over time.
Highlights
The intense use of muscles leads to a decrease in power and performance, known as skeletal muscle fatigue [1]
C57BL/6 (~8 weeks old) mice were randomly assigned to experimental (n = 6) or control (n = 6) groups, both of which were subjected to Chemical exchange saturation transfer (CEST) imaging and 31 P magnetic resonance spectroscopy (MRS)
Because the CEST signal is derived from the metabolite protons that are exchanged with the surrounding water, the signal intensity is affected by the proton exchange rate
Summary
The intense use of muscles leads to a decrease in power and performance, known as skeletal muscle fatigue [1]. This is a complex physiological phenomenon that manifests as a result of various changes in muscle properties, including changes in the concentrations of extracellular and intracellular ions [2,3]. The accumulation of lactic acid and CO2 during muscle activity reduces the cellular pH and subsequently the interstitial pH because of an acid efflux from the muscle cells [4]. Changes in the interstitial pH during muscle activity were suggested to be an important signal in regulating blood flow [4,5,6]. Conventional MRI is capable of providing information on musculoskeletal abnormalities but not on muscle function or fibromyalgia
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