T1- and T2-weighted images are routinely performed in the evaluation of the spine. With Tl-weighting, the intervertebral disc demonstrates fairly homogeneous signal intensity that is slightly less than that of the vertebral body red marrow. Epidural fat can be distinguished by its relatively bright appearance or high signal intensity (1). Nerve tissue, on the other hand, is of low intensity (dark appearance) but may still be differentiated from cerebrospinal fluid (CSF), which appears black with an even lower signal. The thin lines of low signal intensity along the superior and inferior borders of vertebral bodies represent the cortical endplates and have been confirmed by correlation with cadaveric specimens (2).
In contrast to the homogeneous appearance of discs on Tl-weighted images, T2-weighting shows a high signal inner portion surrounded by a low signal outer area (1). The high signal corresponds to the water-rich nucleus pulposus and inner fibers of the annulus fibrosus, which cannot be distinguished with magnetic resonance imaging (MRI). The peripheral low signal areas represent the outer fibers of the annulus (2). CSF has fairly high signal intensity with this sequence, which can be distinguished from the low signal nerve tissue (1) (Fig. 1).
After the age of 30, intranuclear clefts can be observed as horizontal areas of hypointensity (dark areas) in the nucleus. These are normal changes of aging and represent the appearance of fibrous tissue (3,4). Interestingly, this MRI finding does not distinctly correlate with an anatomic structure in cadaveric studies (2).
From: Interventional Radiology of the Spine
Edited by J. Kevin McGraw © Humana Press Inc., Totowa, NJ.
Visualization of the intervertebral foramina and their contents should be performed with both axial and sagittal cuts to ensure adequate delineation of discs, foramina, and nerve roots (1,5). Epidural fat in the neural foramina, which has relatively high signal intensity with T2-weighting, can be differentiated from the very high signal CSF and low intensity nerve tissue, which appears as a filling defect within the CSF (1).
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