染氟兔椎体骨组织形态计量参数与MRI信号强度相关性的研究

Histomorphometryof the vertebra and its correlations with MRI signal intensity in rabbits with fluoride treatment

目的 分析染氟兔腰椎椎体骨和骨髓组织形态计量参数的特点及其与MRI信号强度的相关性。方法 采用40例3月龄新西兰白兔随机分为染氟组（30只）和对照组（10只）,每组雌雄各半。用城市自来水每升加入100 mg氟化钠（氟含量100 mg/L）作为饮用水对染氟组兔染氟180 d,30只中获完整资料24只（雄性10只,雌性14只）;用相同城市自来水（氟含量〈0.9 mg/L）作为对照饮用水,10只中获完整资料8只（雌雄各半）;依腰椎MRI信号强度对染氟并获完整资料的24只分为敏感型和抵抗型。分析椎体骨组织形态计量参数及其与MRI信号强度的相关性,以及MRI诊断早期氟骨症的敏感度和预测氟骨症易感性的可行性。结果 椎体骨小梁容积（trabecular volume,BV）、骨髓造血细胞容积（hemopoietic volume,HV）和间质积液容积（fluid volume,FV）分别与总海绵组织容积（total spongy tissue volume,TV）的比值为18.3%±2.6%、45.2%±6.0%和10.4%±5.7%,对照组分别为14.5%±2.8%、36.3%±7.3%和6.2%±2.1%,染氟组各比值明显高于对照组;脂肪细胞容积（adipocyte volume）与TV的比值,染氟组（26.0%±8.0%）明显低于对照组（43.3%±5.6%）。染氟的24只兔中发现敏感型2只（8.3%,2/24）,抵抗型22只（91.7%,22/24）。BV/TV、HV/TV和FV/TV值,从大到小依次为敏感型、抵抗型、对照组,AV/TV值的变化则相反。MRI信号强度,敏感型T1加权成像（T1 weighted imaging,T1WI）的对比噪声比（contrast to noise ratio,CNR）最小,其次是抵抗型,对照组最大。脂肪饱和法T2加权成像（fat-saturated T2 weighted imaging,FsT2WI）的CNR变化则相反。T1WI与AV/TV值呈正相关,与FV/TV和BV/TV值呈负相关;FsT2WI与FV/TV、BV/TV值呈正相关,与AV/TV值呈负相关。T1WI诊断早期氟骨症椎体CNR界值取≤ 23.2,其敏感度为83.3%,特异度为100%;FsT2WI的CNR界值取 ≥5.7,其敏感度为45.8%,特异度100%。结论 早期氟骨症的特点主要是骨髓脂肪组织细胞增加和骨髓间质积液,即骨髓氟中毒,与MRI信号强度改变相关。

Objective To analyze histomorphometrical characteristics of the bone and bone marrow tissues of the lumbar vertebrae in rabbits with fluoride treatment, and its correlation with signal intensity of MRI. Methods Forty New Zealand albino rabbits aged three months old were randomly divided into fluoride exposure of 30 cases and control of 10 cases, male and female, half each. One hundred milligrams of sodium fluoride were added to the municipal water each liter （fluoride content 100 mg/L） as drinking waterto fluorine for 180 days. Twenty-four of 30 cases with fluoride exposure had complete data （male10 casesand female14 cases）. The same municipal water was used as control drinking water （fluoride content 〈0.9 mg/L）. Eight of 10 cases with control had complete data （male andfemale in half）. Twenty-four cases with fluoride treatment and complete data were classified into sensitive and resistant type according to the MRI signal intensity of the lumbar vertebra. Histomorphometrics of the vertebra and its correlation with the MRI signal intensity, and sensitivity in early diagnosis of osteofluorosis and feasibility of susceptibility to osteofluorosis detected with MRI were analyzed. Results Theratios of trabecular bone volume （BV）, hematopoietic cell volume （HV） and fluid volume （FV） in bone marrow tissue to total cavernous tissue volume （TV） in group with fluoride treatment were 18.3%±2.6%, 45.2%±6.0% and 10.4%±5.7% respectively.These were 14.5%±2.8%, 36.3%±7.3% and 6.2%±2.1% in control group respectively. These parameters in fluoride group were significantly increased compared to control group. The ratio 26.0%±8.0% of adipocyte volume （AV） to TV in fluoride group was significantly lower than that 43.3%±5.6% in control group. Two of 24 cases with fluoride exposure （8.3%, 2/24） were sensitive and the remaining 22 （91.7%, 22/24） were in resistance. The valuesof BV/TV, HV/TV and FV/TV were considered to be sensitive, resistant and control from large to small, while AV/TV value were opposite. A comparison results of signal intensity in MRI showed that vertebra T1WI contrast to noise ratio （CNR） in the sensitive was the minimum （3.0±0.8）, followed by resistance （21.3±3.8） andmaximum in the control （28.3±3.1）, but CNR of FsT2WIwas opposite. There were positive associations between T1WI and AV/TV,FV/TV and BV/TV, and between FsT2WI and FV/TV and BV/TV. There were inverse associationsbetween FsT2WI and AV/TV. Theoptimal threshold value of the vertebra T1WI CNR was 23.2 or lessin early diagnosis of skeletal fluorosis, with sensitivity of 83.3% and specificity of 100%. FsT2WI was 5.7 or more, with sensitivity of 45.8% and specificity of 100%. Conclusion The pathogenesis of osteofluorosis is relative to changes in bone marrow microenvironment and cells number in bone marrow tissue, and is correlated to MRI signal intensity.