Primary Outcome Measures:
- change in advanced magnetic resonance imaging [ Time Frame: immediately after head positions. ]
A change in vertebral, posterior cerebellar and collateral arterial blood flow associated with various head positions and an upper cervical manipulation will be measured using blood oxygen level dependent (BOLD). A BOLD MRI generates a signal by tracking changes in the local oxyhemoglobin to deoxyhemoglobin ratio. Signal changes are due to a combination of altered microvascular perfusion, blood volume, and fluctuations in cellular metabolism. It will also provide more sensitivity in determining the impact of changes in blood flow during the various head positions.
Other: head positions and spinal manipulation
Each subject will then undergo a baseline MRI in a head neutral position (0 degrees rotation). They will then be placed in head rotation (45 degrees) to the non-dominant and undergo a MRI. Maximum rotation to the side with MRI will follow. Finally, each subject will receive an upper cervical rotary manipulation to the non-dominant side with MRI immediately after. A total of 4 test conditions will be evaluated (rest, 45 degree, maximal, post-manipulation). The manipulation will be performed by an experience practitioner on a bed just outside the MRI room in supine position. A controlled impulse load will be applied and the head/neck returned to neutral position. Prior to each maneuver, the subject will be queried on their comfort, condition and willingness to continue
The goal is to further investigate the cerebrovascular hemodynamic consequences of cervical spine positions, including rotation and manipulation in-vivo under clinically relevant circumstances using two advanced forms of MRI technology on the VA and posterior cerebral vessels. According to the knowledge of the investigators, a study utilizing MRI and functional blood oxygen level dependent (fBOLD) imaging to examine blood flow and perfusion, turbulence and evidence of micro-trauma within these vessels has yet to be conducted.