51 Other groups have demonstrated alterations in trigeminal nerve diffusion in trigeminal neuralgia52–55 and
in temporomandibular disorder.56 Figure 3 Somatotopically Organized Activation Patterns of the Human Trigeminal Ganglion Evoked by Noxious Heat to the Ophthalmic (V1), Maxillary (V2), and Mandibular (V3) Facial Regions. Taken together, these studies demonstrate that, at Inhibitors,research,lifescience,medical least for cranial nerves, functional and diffusion MRI can provide mechanistic insight into pain processes at the interphase of the peripheral and central nervous system. SPINAL CORD PAIN IMAGING Positron Emission Tomography (PET) The metabolic rate of glucose increases in the spinal cord during nociceptive in-flow,57,58 affording a mechanism to image spinal pain signaling using 18F-fluorodeoxyglucose. We found no studies demonstrating altered spinal PET ligand uptake in pain, but such
an endeavor appears possible if there is massive peripheral Inhibitors,research,lifescience,medical signaling. FDG is routinely used in oncological staging, and a retrospective analysis of cancer pain patients might demonstrate elevated FDG uptake in corresponding segments of the spinal cord. Ideally, such a study would utilize high-resolution PET in combination with MR or CT to delineate the spinal cord cross-section in multiple voxels, allowing assessment of anterior and posterior segments, and possibly lateralization effects. To see more illustrate Inhibitors,research,lifescience,medical Inhibitors,research,lifescience,medical PET imaging of the spine, we present mean FDG standardized uptake values (SUV) obtained from two studies of 92 patients59 and 30 patients60 without spinal malignancy (Figure 4). Figure 4 Midline 18F-FDG PET/CT of a Healthy Spinal Cord. Magnetic Resonance Imaging Structural MRI is used routinely to assess spinal cord injuries, but due to the spine’s small cross-section, and noise sources such as motion, cerebrospinal fluid (CSF) pulsation, and magnetic susceptibility, functional imaging of the spine is technically challenging. Recent developments in MR sequences and post-processing have opened up the field, and
it is possible to define structure and function Inhibitors,research,lifescience,medical with greater specificity.61 The first functional spinal cord imaging results were published in 1999, indicating that 3-tesla imaging of the cervical whatever spinal cord showed that repeated hand exercise led to a blood-oxygenation level dependent (BOLD)-like increase in spinal cord signal, predominantly on the ipsilateral spinal cord between C6 and T1.62 Since then, spinal fMRI has been reported using multiple paradigms (pain, motor, vibration, light touch) in healthy subjects and in patient populations including carpal tunnel syndrome, spinal cord injuries, and multiple sclerosis. These studies, along with methodological advances, are the subject of two excellent reviews on state-of-the-art spinal cord imaging methods63 and applications64 that we refer the reader to for full details.