title: Potential false-negative MR images of the thoracic spine in disk disease with switching of phase- and frequency-encoding gradients.
abstract: Two patients with thoracic disk protrusion were evaluated with magnetic resonance imaging. A T1-weighted spin-echo sequence was used, with and without switching of the phase- and frequency-encoding gradients. Both disks were well delineated when the frequency-encoding gradient was parallel to the spinal axis. When the gradients were switched (with the phase-encoding gradient parallel to the spinal axis), both herniated disks were partially obscured by a posteriorly displaced fat signal from marrow, caused by a chemical shift artifact. In addition, the anterior subarachnoid space appeared falsely narrowed, and the cerebrospinal fluid (CSF) signal intensity was increased, which reduced the CSF-cord contrast. These findings suggest that switching the orientation of the frequency- and phase-encoding gradients may result in false-negative T1-weighted sagittal images of the thoracic spine.
mesh_terms: D000328:Adult; D001416:Back Pain / Q000175:diagnosis; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology; D007405:Intervertebral Disc Displacement / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D013346:Subarachnoid Space; D013904:Thoracic Vertebrae / Q000473:pathology*