| 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.