Measuring the neural response to continuous intramuscular infusion of hypertonic saline by perfusion MRI

To determine the extent to which arterial spin labeling (ASL), a functional magnetic resonance imaging technique that directly measures cerebral blood flow (CBF), is able to measure the neural activation associated with prolonged experimental muscle pain.

Hypertonic saline (HS) (5% NaCl) was infused into the brachioradialis muscle of 19 healthy volunteers for 15 min. The imaging volume extended from the dorsal side of the pons to the primary somatosensory cortices, covering most of the cortical and subcortical regions associated with pain perception.

Using a numerical scale from 0 to 10, ratings of pain intensity peaked at 5.9 ± 0.5 (mean ± SE). Group activation maps showed that the slow infusion of HS evoked CBF increases primarily in bilateral insula, with additional activation in right frontal regions. In the activated areas, CBF gradually increased at the onset of HS infusion and was maintained at relatively constant levels throughout the remainder of the infusion period. However, the level and extent of activation were smaller than observed in previous studies involving acute muscle pain.

This study demonstrates the ability of ASL to measure changes in CBF over extended periods of time and that the neural activation caused by muscle pain is paradigm specific.