Using Perfusion MRI to Measure the Dynamic Changes in Neural Activation Associated With Caloric Vestibular Stimulation
Condition: Chronic Pain
MeSH terms: Chronic Pain
Study type: Interventional

Summary: 
      The investigators propose that Arterial Spin Labelling Functional Magnetic Imaging will be
      able to capture functional changes associated with caloric vestibular stimulation and better
      delineate the etiology of the pain augmentation that has been documented with this
      intervention.
    

Detailed description: 
      There has been recent success in utilizing the non-invasive caloric vestibular stimulation as
      a means of modulating chronic pain. Caloric stimulation involves cooling the ear canal with
      either water or a cooling probe to induce vestibular stimulation. This is a technique
      frequently performed as part of a neurologic exam.

      The current theory of how caloric vestibular stimulation regulates pain is by thermosensory
      disinhibition. Temperatures below 25 C activate both cold thermoreceptors (Aδ fibers) and
      also C-nociceptors. These inputs pass in the spinothalamic tract to the thalamus, where the
      C-fiber input goes to the anterior cingulate cortex (ACC) and the Aδ fiber input passes to
      the thermosensory cortex in the dorsal posterior insula (dpIns). It is proposed that CVS
      reduces central pain by activating the parieto-insular vestibular cortex. As this area is
      anatomically adjacent to dorsal posterior insula, it may cross-activate it to suppress the
      ACC, or given both these cortical areas share pathways in the brainstem this may be the
      mechanism by which pain is suppressed.

      Our team has successfully demonstrated arterial spin labeling (ASL), among other functional
      magnetic resonance imaging modalities, to capture functional changes in cerebral processing
      related to pain. This utilizes the principle that increases in cerebral blood flow to a
      specific region of the cortex is a marker for increased functioning of this region,
      conversely a decrease of blood flow to a specified region is a correlate of down regulation
      of this specific region. We propose that ASL will be able to capture functional changes
      associated with caloric vestibular stimulation and better delineate the etiology of the pain
      augmentation.

      All functional studies will be conducted on a 3 Tesla scanner equipped with an 8-element,
      receive-only head coil. Each subject will lay in a supine position on the MRI table with
      their head immobilized by foam padding and a chinstrap. Every study will begin by collecting
      high-resolution anatomical images using a three-dimensional spoiled GRASS (Gradient Recalled
      Acquisition in Steady State) sequence. These structural images will be used for placement of
      the functional images and for anatomical atlas transformation in the image processing. The
      perfusion-weighted images will be acquired with a pulsed arterial spin labeling
      (non-invasive) approach. Once the baseline perfusion weighted functional images have been
      attained a continual functional image acquisition sequence will begin. During this phase the
      subject will have a series of three 30 second cooled ear canal irrigations separated by 60
      seconds. The water will be cooled to 18 degrees Celsius using an ice water combination and
      standard thermometer. The irrigation will be administered at 2cc per second (total of 30cc
      per ear over 30 seconds) via an MRI compatible infusion pump through a modified stethoscope
      with perforations to ensure there is no possibility of pressure build-up within the canal.
      Following this series, perfusion weighted images will be collected for a subsequent
      10minutes. Subjects will be welcome to discontinue from the study at any time they see fit.
      Each functional study will comprise 24.5 minutes. 10 minutes of baseline imaging 5.5 minutes
      of initial functional imaging, 4.5 min of caloric vestibular stimulation and 5.5 minutes of
      repeat functional imaging.

      Images are to be reconstructed using software written in IDL (Interactive Data Language,
      Research Systems, Boulder, CO). Functional image pre-processing and statistical analyses will
      be performed with Statistical Parametric Mapping software (SPM2, Wellcome Department of
      Imaging Neuroscience, University College London, UK, http://www.fil.ion.ucl.ac.uk/spm). The
      end data will be a measurement, in percentage change, of blood flow to specific anatomic
      regions of the cortex.
    

Intervention name(s): Caloric Vestibular Stimulation
Intervention type(s): Procedure
Other intervention name(s): Caloric vestibular stimulation performed by a modified stethescope ear attachment attached to an MRI compatible infusion pump.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Caloric Vestibular Stimulation; Functional Imaging