Noninvasive Estimation of Temperature and pH in Human Lower Leg Muscles using ¹H Nuclear Magnetic Resonance Spectroscopy

Abstract

The temperature and pH of human lower leg muscles were estimated noninvasively using 1 H‐NMR spectroscopy at 3.0 and 1.5 T on five normal volunteers (21M, 24M, 27M, 34M, 47M). The chemical shifts of water and imidazole protons relative to cholines (–N + CH 3 ) or creatines (–CH 3 ) could be used as the temperature and pH probes, respectively [1–4]. Using the chemical shift, estimated values of the temperature in gastrocnemius (GAS; shell region) and soleus muscles (SOL; core region) under ambient temperature (21–25°C) were 33.6±0.4 and 35.3±0.4°C (mean±SE), respectively (significantly different; P < 0.01). The values of pH in these muscles were estimated to be 6.97 ± 0.01 and 6.96 ± 0.02, respectively. Alternation of the surface temperature of the lower leg from 40 to 10°C significantly changed the temperature in GAS (P < 0.0001) from 35.8 ± 0.4 to 26.2 ± 1.2°C and the pH in GAS rose from 6.95 ± 0.01 to 7.01 ± 0.01 (P <0.01). However, the values of pH and temperature in SOL were not significantly affected by this maneuver. These results indicate that the pH in GAS was moderately changed by muscle temperature ( r = –0.59, P <0.01), and its change was estimated to be –0.005 pH units/°C.