The bright intervertebral disk: an indirect sign of abnormal spinal bone marrow on T1-weighted MR images.

Two phantoms were constructed and imaged for the purpose of reproducing and understanding the relatively increased signal intensity of intervertebral disks on T1-weighted MR images in three patients with diffuse vertebral metastases. The first phantom simulated a normal spine and showed that the disks and vertebral bodies were of similar intensity. The second phantom simulated an abnormal spine and showed that the disks were brighter than the vertebrae. Prolonged relaxation times from the vertebral bodies as well as manipulation of the window width and level are the factors responsible for the presence of bright disks on T1-weighted images. Variations in the window width and level can accentuate the apparent increase in signal intensity from the disks but not reverse it. Although the presence of bright disks may be subtle, recognition of this sign should raise the possibility of diffuse replacement of normal fatty bone marrow in the vertebrae.