Objective

Avascular necrosis of the femoral head (ANFH) is a pathological process that results from interrupted or impaired blood supply to bone, involving osteocyte and bone marrow component death and subsequent repair. ANFH ultimately leads to structural changes, collapse, and dysfunction of the femoral head. Semi-quantitative scoring is an established method for evaluating ANFH magnetic resonance imaging (MRI) datasets in observational studies and clinical trials. Advanced quantitative MRI techniques may improve the assessment of femoral head composition.The Dixon MR imaging sequence can be used for characterization of musculoskeletal pathologies by calculating the water/fat ratio of the femoral head. In our study, we assessed ANFH using Dixon MR imaging by detecting the changes in femoral head water/fat ratio.

Material and Methods

Twenty ANFH patients (11 males, 9 females, age 21-58, average age 39) and 22 healthy people with matched age and gender were included in this study. The primary symptoms in ANFH patients were hip joint pain, tenderness, and radiating pain. All patient cases were confirmed with femoral head necrosis by conventional MR imaging findings.MRI data were collected on a MAGNETOM Trio 3T MR scanner (Siemens) with a 6-channel body matrix Coil. The multi-echo3D Dixon sequence (TR = 9.1ms, TE =1.23, 2.48, 3.73, 4.98, 6.23, 7.48ms, voxel size: 2.0×1.6×2.0mm3, FOV:400×400mm2) was used to measure the water/fat ratio of femoral head．The water/fat permillage of the femoral head was calculated.A double factor variance analysis was performed to compare femoral head water/fat permillage between ANFH patients and the healthy controls.

Results

Of the 20 ANFH patients (40 joints), there were 8 cases with bilateral osteonecrosis and 12 cases with unilateral osteonecrosis. The 40 joints were divided into an osteonecrosis of the femoral head (ONFH) group (28 joints) and a contralateral (CONT) group (12 joints). 44 joints in the healthy group (HEA) were also observed. Differences in water/fat permillage between the three groups were statistically significant (F=9.58, p=0.000, η2=0.19). The water/fat permillage of the ONFH group was significantly higher than that of the HEA group. The fat permillage of the ONFH group was significantly lower than that of the HEA group (Fig.1).

Discussion

Radiographic studies are limited to the depiction of joint space and of cancellous subchondral bone changes. Often, T2-weighted images aid in the detection of necrotic tissue for ANFH lesions that mostly show ill-delimited edema-like marrow changes. Semi-quantitative assessment is a widely accepted method for evaluating large MRI datasets in observational clinical trials of the hip. The multi-echo 3D Dixon technique provides the water/fat ratio quantification for evaluation of the bone marrow edema and the stage of ANFH. Our study demonstrated that femoral head water/fat permillage in ANFH was significantly higher than that of the healthy hips. The findings demonstrated that the measurements of femoral head bone marrow edema can be used to describe ANFH at the early stage.

Conclusion

The multi-echo 3D Dixon MR imaging provides a promising method of measuring femoral head water/fat permillage in ANFH patients. This technique reliably describes femoral head bone marrow edema and may improve the diagnostic accuracy for ANFH.

Acknowledgements

No acknowledgement found.

References

Zhong X, Nickel MD, Kannengiesser SAR, Dale BM, Kiefer B, Bashir MR. Liver fat quantification using a multi-step adaptive fitting approach with multi-echo GRE imaging.MagnReson Med 2014;72:1353-1365.