MR imaging of the spine after radiation therapy: easily recognizable effects.

Magnetic resonance (MR) imaging of the spine after radiation treatment in four patients demonstrated well defined areas of increased signal intensity in the vertebral bodies on short or T1-weighted sequences. Radiation doses of 4000-5790 rad (40-57.9 Gy) were administered to the mediastinum, rectum, and spine. The interval between radiation treatment and MR imaging was 2 months to 10 years. The abnormally increased areas of signal intensity seen on MR images were best demonstrated in the midsagittal plane and were easily differentiated from involvement by tumor. The alteration in signal intensity probably was secondary to replacement of marrow by fatty tissue and corresponded closely with radiation therapy portals.