fMRI changes in the brain associated with the carotid compression test

The purpose of our investigation was to study in normal volunteers the response to a unilateral common carotid (CC) compression test using dynamic MRI sensitive to variations in blood magnetic susceptibility.

Nine volunteers, positioned in a 1.5 T MR scanner, performed a unilateral 40 to 45 s CC self-compression during the acquisition of single slice axial T2*-weighted FLASH images.

In three subjects, the signal showed a significant 2% drop from baseline in the ipsilateral frontal temporal cortex during the compression. In another three subjects, a significant 1.5-2% signal decrease was observed in both hemispheres. In two subjects whose MR angiography showed abnormalities of the circle of Willis, the bilateral signal drop was more remarkable (3%). In one volunteer, the signal did not change.

Increased deoxyhemoglobin within the brain microcirculation is the probable explanation for the signal drop. This method could be further tested in view of the widespread use of open interventional MR units.