How is femoral osteonecrosis detected?

Q: I am in my mid 40s and have this aching hip pain that radiates to my knee.  Someone told me that I might have femoral osteonecrosis. How is this detected?  How do they determine how bad it is?

A: An MRI is the gold standard for femoral osteonecrosis detection.  Surgeons determine the stage of the disease progression by location, size, and amount of swelling present.

Reference: Charalampos G. Zalavras, M.D. and Jay R. Lieberman, M.D. Osteonecrosis of the Femoral Head: Evaluation and Treatment. The Journal of American Academy of Orthopedic Surgery. July 2014. Vol. 22, No. 7. Pp 455-464.