Radiotherapy effects on vertebral bone marrow: easily recognizable changes in T2 relaxation times.

The effect of localized radiotherapy on vertebral bone marrow was demonstrated in two patients using quantitative MRI studies with pixel-by-pixel measurement of T2 relaxation times with generation of T2 images. Conventional T1-weighted spin-echo images were obtained as well. Irradiated vertebral bone marrow was found to have longer T2 relaxation times than the neighboring nonirradiated bone marrow. These changes corresponded to the increased signal intensity on T1-weighted images and to the field of radiotherapy and were noted 2.5 to 32 mo after radiotherapy. Radiologists should be aware of the increased T2 relaxation times in irradiated bone marrow to correctly assess spinal disorders in irradiated patients. The reported T2 changes may reflect the abundance of adipose cells that proliferate in bone marrow after radiotherapy, or may indicate an additional histological change, such as bone marrow necrosis or edema. Conclusive histological proof remains to be obtained.