BACKGROUNDIt is of value to identify the non-invasive means that can accurately reflect the blood supply of epiphysis and is more sensitive in detection of early ischemia of epiphysis than the conventional gadoteridol (Gd)-enhanced SE T1WI. The aim of this study was to evaluate the blood supply of various anatomic regions at the end of normal growing long bone using dynamic Gd-enhanced MR imaging and compare the sensitivities between dynamic Gd-enhanced MR imaging and conventional Gd-enhanced SE T1WI in the detection of decreased blood perfusion of early epiphyseal ischemia.

METHODSTwenty-seven two-week-old piglets were used in this study. For the study of the end of normal growing long bone, unilateral MR imaging of the distal femur and proximal tibia was performed on eleven piglets. The comparison was made among various anatomic regions (physeal and epiphyseal cartilage, metaphyseal spongiosa, the secondary ossification center and metaphysis) using MRI in terms of the enhancement ratio and speed. Their relationships with the histological findings, including RBC/mm(2) and vessel distribution, were evaluated. To examine ischemic femoral head, 16 piglets were divided into two groups, with the control group having 8 piglets (involving 16 normal hips) and an ischemic group having 8 piglets (involving 16 hips with hyperabduction). In the ischemic group, MR imaging was performed on the hips in the hyperabduction immobilized persistently for 30 minutes. After MRI, the piglets were allowed to ambulate freely for 1 day and the same MR scanning was then repeated in a neutral position. The difference in enhancement ratio and speed of the femoral head between the control and ischemic group were evaluated.

RESULTSWith regard to the end of normal growing long bone, the enhancement ratio of the metaphyseal spongiosa was greatest among all the anatomic regions (P < 0.001). The enhancement ratio of physeal cartilage was greater than that of epiphyseal cartilage (P < 0. 001), which was the lowest in all tissues (P < 0.001). The enhancement speed of the spongiosa was greater than that of physis but the difference was not significant (P > 0.05). The enhancement speed of physis was greater than that of epiphyseal cartilage (P < 0.05), which was the lowest among all the tissues (P < 0.05). The enhancement ratio and speed were found to be related to the histological findings, including RBC/mm(2) (R > 0.75) and distribution of vessels in the tissues. With ischemic femoral head, the enhancement ratios of physis, anterior part and posterior part of capital femoral epiphysis were significantly lower (P < 0.05) and enhanced more slowly (P < 0.05) than those of normal femoral head on dynamic Gd-enhanced MR imaging. On conventional Gd-enhanced SE T1WI, however, no apparent decrease in enhancement ratio and speed in ischemic hips was found (P < 0.05), when they were compared with those in the normal hips.

CONCLUSIONSDynamic gadoteridol-enhanced MR imaging can reveal the blood supply in various anatomic regions of the end of normal growing long bone. It is more sensitive than conventional Gd-enhanced SE T1WI in the detection of early epiphyseal ischemia.