Detection of acute avascular necrosis of the femoral head in dogs: dynamic contrast-enhanced MR imaging vs spin-echo and STIR sequences.

Abstract

Spin-echo MR imaging has been shown to be highly sensitive in the detection of avascular necrosis. Very early avascular necrosis can, however, appear normal on MR images. We compared dynamic contrast-enhanced MR imaging with conventional spin-echo and short Tl inversion-recovery (STIR) sequences for detecting acute osteonecrosis in an animal model. Avascular necrosis was induced unilaterally in the femoral heads of five dogs that were imaged with a 1.5-T system within 3 hr of devascularization. After standard T1-weighted, T2-weighted, and STIR images, gradient-recalled echo images, 28/5 (TR/TE) with a 45 degrees flip angle, were obtained at 6-sec intervals for 90 sec synchronous with the IV administration of 0.2 mmol of gadoteridol per kilogram of body weight at a rate of 2 ml/sec via an automated injector. Two animals were reimaged after 7 days. Spin-echo and STIR images did not show any acute changes in the ischemic femoral heads. In contrast, significant differences were present in the enhancement profiles of the marrow spaces in the normal and ischemic femoral heads (p = .005). Normal marrow was characterized by rapid enhancement, with an average signal intensity increase of 83% peaking at 36 sec; no measurable enhancement was seen in the marrow of the ischemic femoral head. Spin-echo images, obtained 7 days after devascularization (n = 2), showed changes characteristic of avascular necrosis. Dynamic contrast-enhanced MR images showed persistent lack of enhancement in the avascular marrow of the ischemic femoral head. A junctional zone, characterized by rapid contrast enhancement in excess of 120% without early washout, was identified at the interface between normal and avascular marrow. In this experimental model, dynamic contrast-enhanced MR imaging proved significantly more sensitive than conventional spin-echo and STIR imaging in the detection of acute avascular necrosis.