Four classes of AVN: Mitchell classification in MRI

The MRI staging classification of Mitchell et al.describes four classes of AVN based on the signal characteristics within the center of the lesion on T1 and T2-weighted images. This classification may be useful in grading lesion acuity, as infarcted bone will tend to progress through the classes of signal intensity over time. However, this progression is not always consistent, and more than one class of signal abnormality may be found in a single lesion.

Class T1 T2 Definition A Bright intermediate "fat" signal B Bright Bright "blood" signal C intermediate bright "fluid or edema" signal D dark dark "fibrosis" signal