The double-line sign of osteonecrosis: evaluation on chemical shift MR images

The MR appearance of osteonecrosis was assessed on selective fat and water images to further evaluate the features of the double-line sign of osteonecrosis. Conventional T1- and T2-weighted spin-echo and frequency selective chemical shift images of eight patients with avascular necrosis of the femoral head and three patients with bone infarcts were retrospectively reviewed. Eight of 11 patients showed a double-line sign on T2-weighted spin-echo images. In these cases correlation with selective water images revealed that a chemical shift artifact contributed to the appearance and location of the hyperintense line. The double-line sign was not seen in three patients with radiologically and clinically proven osteonecrosis. It is concluded that chemical shift imaging improves our understanding of the nature of the double-line sign.