|Class A||osteonecrotic lesion shows signal similar to fat – high on T1, intermediate on T2|
|Class B||hips show signal of blood or hemorrhage (high on both T1 and T2)|
|Class C||hips show signal of fluid (low on T1, high on T2)|
|Class D||hips show signal of fibrous tissue (low on T1 and T2)|
Peripheral band of low signal intensity seen in all classes. Border visible on T1 in Class A and B and T2 in Class C and D.