Proton Magnetic Resonance Spectroscopy ─ Evaluation of lipid Composition and Assessment of Avascular Necrosis of the Femoral Head
Date Issued
2006
Date
2006
Author(s)
DOI
zh-TW
Abstract
The etiology of avascular necrosis of the femoral head might be thromboembolism of small vessels, increased venous pressure and vasculitis. Increased intraosseous pressure is an important factor of the occurrence of avascular necrosis of the femoral head. The changes of the intramedullary, extravascular component not only influence the intraosseous pressure, but also alter the blood perfusion of the femoral head. The cancellous bone make the bone marrow space septated into many small, closed chamber within the femoral head. Thus, only minimum alteration in the intramedullary component can increase the intraosseous pressure of femoral head and make the small vessel collapsed. Impaired blood perfusion and then ischemia developed subseguently. The major component within the femoral head is the fatty tissue of its yellow bone marrow. The medication of corticosteroid is an important predisposing factor of avascular necrosis, the steroid can cause fat cell hypertrophy and abnormal deposition. The steroid can also stimulate the osteoprogenitor cells to express a fat cell specific gene, 422(aP2), and to differenciate into adipocytes. Based on these above mentioned reasons, the investigator plan to figure out the change of fat component within the bone marrow of femoral head, and may have more understanding and prediction about avascular necrosis.
According to the previous report, the evaluation of avascular necrosis was majorly based on the proton magnetic resonance image, such as T1 and T2 weighted images and enhancement pattern with contrast agent injection. The proton magnetic resonance spectroscopy (1H MRS) was never used. The 1H MRS was commonly used in evaluating the cerebral disorders, such as epilepsy and acute infarction. The fat itself has plenty of proton and 1H MRS will to be the appropriate method evaluate the fat tissue. The water also had plenty amount of proton. Thus, we consider the possibility to evaluate the ratio of intraosseous fat and water by using the proton MRS. In recent years, several investigators started to use the PRESS, STEAM or QCSI technignes to study the fat and water component of human vertebral body. They also found the lipd-water ratio demonstrated by 1H MRS was abnormal in patients with leukemia, aplastic anemia and Gaucher disease. The therapeutic result was also followed by 1H MRS. Not only the patients, but also the normal subjects were studied with 1H MRS according to different age and gender.
In phase I of the study, we applied the proton MRS examination on the intact femoral heads of patients with unilateral osteonecrosis of hip. These hips are symptomless and normal on plain films and MRI films. Age-matched controls without hip problems were also measured. Our results revealed significant difference between these two groups in the lipid and water components of the femoral heads.
However, due to lack and impossibility of biopsy, we can not be certain that the differences indicate early change of osteonecrosis. In addition, it is a cross-sectional study without long-term follow-up, we also can not be sure that the MRS can diagnose osteonecrosis earlier than MRI, nor as a prognostic predictor.
Therefore, we perform MRI and MRS study again after at least two years. It is the phase II of the study. We expect that some patients should develop osteonecrosis on their previously intact hips.
According to our literature review, femoral head avascular necrosis is related to epiphyseal scar after adulthood. Some people have complete epiphyseal scar which separates the blood supply from femoral neck to femoral head; others have incomplete epiphyseal scar. These patients with complete epiphyseal scar have higher osteonecrosis rate.
Therefore we perform MRS study both on femoral head and femoral neck region. We divide our patients into “complete” and incomplete” groups. We are curious that whether these two groups have different MRS waveform, that is, different lipid and water component.
In phase II, MRS was performed on the intact hips of 38 patients with unilateral femoral AVN. They were followed and MRS study was performed after at least two years. The lipid spectrum on the MRS was further divided into three peaks, at 2.1ppm, 1.2ppm and 1.0ppm . Three variables were used to describe each peak: integration, amplitude, and line width. The completeness of epiphyseal scar was also recorded as a prognostic factor.
10.5% (4/38) patients developed a new AVN lesion on the previous intact femoral heads in a two-year follow-up period. They are all male. In lipid peaks at 2.1 and 1.0ppm, the integration showed significant differences between these four patients and the rest 34 patients (p<0.05). In the lipid peak at 2.1ppm, the amplitude showed significant differences (p<0.05). The risk of AVN progression is not related to the completeness of epiphyseal scar.
The lipid peak at 2.1ppm showed significant change in the patients who was prone of develop new AVN lesions. According to the literature, these part of the lipid may represent the ester group. In other words, the lipid composition had changed, by transforming its chemical compounds in certain ways, in the high risk patients. Further animal study and pathologic examination is required to correlate the spectroscopic findings.
The lipid spectrum of MRS on the femoral head at risk of AVN could play a role in predicting its prognosis of possible progression into AVN, as early as two years.
Subjects
磁振造影
氫原子頻譜儀
股骨頭
缺血性骨壞死
非外傷性
類固醇
脂肪增生
骨髓
脂類
水份
Magnetic Resonance Image (MRI)
Proton Magnetic Resonance Spectroscopy (1H MRS)
Femoral Head
Avascular Necrosis
Non-traumatic
Corticosteroid
Lipogenesis
Bone Marrow
Lipid
Water
SDGs
Type
text
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