Signal intensity changes in T2-weighted MR image of the human trapezius muscle upon cold pressor stimulation.

OBJECTIVE: The ability to measure hemodynamics of skeletal muscle proper is one of the major goals for muscle pain researchers. The aim of the present study was to evaluate the ability of signal intensity (SI) in T2-weighted trapezius muscle magnetic resonance imaging (MRI) to detect intramuscular hemodynamic changes during cold pressor stimulation (CPS). MATERIALS AND METHODS: Fifteen healthy volunteers (mean age, 25.9+/-2.1 years) participated in this study. T2-weighted MRI was acquired using a 1.5 tesla MR unit with a body array coil. The slice level was set perpendicular to the muscle long axis at the mid-point of the horizontal portion of the right trapezius muscle. Cold pressor stimulation (4 degrees C) was applied to each subject's right foot and ankle for 2 min. The SI changes were recorded continuously for 7 min before, 2 min during, and 6 min after withdrawal of cold pressor stimulation. Six of these subjects also underwent a mock-CPS trial. RESULTS: The mean SI level in T2-weighted trapezius muscle MRI significantly increased during CPS (P<0.0001, one way repeated measure ANOVA) and returned to the baseline level after cold pressor withdrawal. No statistically significant signal changes were observed across the mock-CPS trial subjects. These findings are identical to the cold pressor-induced hemodynamic changes documented in the trapezius muscle by near-infrared spectroscopy evaluation. CONCLUSIONS: SI measurement in T2-weighted trapezius muscle MRI is sufficiently sensitive to detect intramuscular hemodynamic changes during CPS.

Correlation of the near-infrared spectroscopy signals with signal intensity in T(2)-weighted magnetic resonance imaging of the human masseter muscle.

The purpose of this study was to compare and contrast blood volume changes transcutaneously measured using near-infrared (NIR) spectroscopy against water signal intensity changes taken from a transverse T(2)-weighted MR image of the masseter muscle in healthy human subjects before, during and after contraction. Eight healthy non-smoking males with no history of chronic muscle pain or vascular headaches participated (mean age: 23.9+/-0.6 years). The MRI data were gathered using a turbo spin echo sequence (TR: 2300 ms; TE: 90 ms; FOV: 188x300 mm; scanning time: 30 s; slice thickness: 10 mm) and the slice level was set at the mid-point between the origin and insertion of the masseter. Intramuscular haemoglobin (Hb) levels and water content of the right masseter muscle were continuously monitored for 2 min before, 30 s during and 15 min after a maximum voluntary clenching (MVC) task. Both the near-infrared and MRI data were baseline-corrected and normalized and mean levels were established and plotted. Plots of the data showed that both near-infrared-based total Hb and T(2)-weighted MRI-based signal-intensity levels clearly decreased during contraction and a clear post-contraction rebound response was evident after the contraction. The near-infrared data were found to be highly correlated with MRI-based signal-intensity data (Pearson's r=0.909, P<0.0001). In conclusion, these data provide powerful evidence that near-infrared data (total Hb), transcutaneously taken from the masseter muscle in humans, will reflect the intramuscular water signal intensity changes seen using a T(2)-weighted MRI imaging method.

Intramuscular haemodynamic responses to different durations of sustained extension in normal human masseter.

Ten healthy non-smoking males (mean age 24.3+/-0.8 years) with no history of chronic muscle pain or migraine participated in this study. Intramuscular total haemoglobin (Hb), an indicator of blood volume in the illuminated area, was measured with a non-invasive, near-infrared spectroscopic device. Each participant was told to maintain maximal mouth opening to extend the masseter muscle for 30, 60 or 120 s in random order. Data were continuously recorded from the right masseter 1 min before, at set times during and for 5 min after sustained muscle extension in each trial. Each trial was separated by a 10-min interval. Heart rate (HR) and blood pressure (BP) were also recorded. The mean normalized Hb decreased during muscle extension and rebound hyperaemia was observed after it in each trial (P=0.0001). Hb returned to baseline within 60 s. The magnitude of the decremental change during extension and of the incremental change in the rebound hyperaemia was not significantly different among the three trials (P=0.9071); neither were mean normalized HR and BP. These data suggest that sustained extension of the masseter produces a reduction in total intramuscular Hb during extension and a secondary increase in Hb following a return to the resting muscle's normal length.