Patients who require long-term or large doses of steroids are at high risk for osteonecrosis. Early diagnosis of this complication is essential as the prognosis is affected by the stage of the disease. However, there is no consensus on whether screening of bone necrosis should be performed using glucocorticoids. Magnetic resonance imaging (MRI) is more sensitive than plain film for diagnosing early-stage bone necrosis._¹ But MRI is not able to reflect the physiology of osteonecrosis. It is well known that osteonecrosis of the femoral head (ONFH) is due to ischemia and anoxia of the femoral head. Thus, blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) is sensitive to the dynamics of the blood oxygenation levels and usually has a wide application prospect for ONFH. This study attempted to compare BOLD-MRI with conventional MRI sequences for determining the onset of osteonecrosis of the femoral head following steroid-related osteonecrosis.In the present study, 112 patients who had received steroid treatment were scanned using conventional MRI and BOLD-MRI using 3T MRI scanner (Achieva Intera; Philips Medical Systems, Best, the Netherlands).The study examined 15 hip joints from 9 cases with early ONFH. Specifically, the 9 cases were followed up at 1 month, 4-5 months, 7-8 months and 12-13 months after steroid therapy. We use the conventional MRI (T2WI/TSE, SPAIR/PDW in coronal view, and SPAIR/T2WI, 3D/WATS in axial view) and BOLD-MRI sequence (TR=15ms, 8echos, TE=9.21/18.42/27.63/36.84/46.05/55.26/64.47/73.68ms, FA=30°, matrix size=312×429, FOV=250×429mm, slice thickness=2.5mm ) to compare the hip joint between the 9 patients with osteonecrosis of the femoral head as above and the hip joint of 10 healthy controls. With the section cross the fovea of femoral head, we set six ROIs on the section (Fig. 1) and then analyzed morphological performance on routine MRI sequences between normal control group and patient group with femur avascular necrosis. Moreover, R2* value change in the suspicious uninjured side of patients with unilateral disease, R2* value change in a patient in different time, and the difference between R2* image and routine sequences in the lesion area in a patient were also explored.In the control group, the values of zone 4 and 1 were the highest, followed by zones 6 and 3, with zones 5 and 2 showing the lowest values (Table 1). This phenomenon indicated that the blood flow and volume had regional maldistribution in the femoral head. On conventional MRI, zones 1, 2 and 3 were the most common zones involved. In the affected femoral head, the R2* value significantly decreased for zones 1 and 4, which were the most sensitive zones. Some patients’ affected regions in R2* mapping were larger compared to their counterparts in conventional sequences, especially in patients who received steroid therapy for more than four months(Fig. 2, 3).The necrosis area of femoral head was confined to the zone 1~3, which accompanied by the thromboembolism. Unlike previous studies using BOLD-MRI to detect abnormality in fat, kidney and so on,^2,3 both oxyhaemoglobin and deoxyhemoglobin decreased in the lesion and therefore the R2* value in osteonecrosis zone reduced. Because of ligamentum capitis femoris, the oxyhaemoglobin concentration of zone 2 and 5 was higher than the other areas, leading to the significant difference between the value in zone 1 and 4.This study showed that BOLD-MRI is a sensitive modalityfor ischemia detection and ismore sensitive than conventional sequencesin patients. The decrease in the R2*value in steroid-associated ONFH would take place beyond stage I. The manifestation in BOLD-MRI is in accordance with the pathology of ONFH, which would allow early treatment of ONFH.