腹部脂肪含量对低毫安定量CT测量腰椎体模骨密度的影响

Effect of abdominal adipose content on spine phantom bone mineral density measured by low-mA Quantitative CT

目的 评估不同含量腹部脂肪对低毫安定量CT(quantitative computed tomography, QCT)测量腰椎体模骨密度(bone mineral density, BMD)准确性的影响。方法 选取不同面积的新鲜猪离体皮下脂肪包裹于欧洲腰椎体模(European spine phantom, ESP)周围,模拟人体腹部不同含量总脂肪组织(total adipose tissue, TAT),根据TAT面积分为四组:TAT=0、200、320、420 cm^(2)。利用常规QCT及低毫安QCT对每组体模重复扫描10次,测定L1~3椎体BMD值。采用单样本t检验分析低毫安QCT测量值与体模真实值之间的差异。利用单因素方差分析Tukey检验,比较不同TAT条件下低毫安QCT测量值组内差异。以配对样本t检验比较常规QCT与低毫安QCT之间各椎体BMD测量值的差异。计算并比较BMD测量值的均方根误差(RMSE);以Pearson相关分析观察RMSE与TAT的相关性。结果 TAT=0、200、320 cm^(2)时,常规QCT和低毫安QCT测量值间差异均无统计学意义(P>0.05);而TAT=420 cm^(2)时,两种扫描方式的测量值间均具有显著差异(P<0.05)。TAT=420 cm^(2)组,常规QCT的RMSE均小于低毫安QCT。低毫安QCT的RMSE与TAT呈显著正相关;不同TAT条件下,L1椎体的RMSE均大于L2及L3椎体。结论 对于一般人群,低毫安QCT可以准确测量腰椎BMD,并且在辐射剂量方面具有极大优势;而对于超重/肥胖人群,使用常规QCT测量腰椎BMD比低毫安QCT要准确。

Objective To investigate the effect of different amounts of abdominal adipose on the accuracy of low-mA quantitative computed tomography(QCT) measurements of bone mineral density(BMD) in a spine phantom model. Methods Fresh porcine fat of different areas were wrapped around the European Spine Phantom(ESP) to simulate different contents of total adipose tissue(TAT) in human abdomen, which were divided into four groups according to TAT area: TAT=0 cm~2, 200 cm~2, 320 cm~2, and 420 cm~2. The BMD values of the L1-3vertebrae were measured using routine QCT and low-mA QCT with 10 repeated scans for each group of body models. A one-sample t-test was used to analyze the differences between the measurements obtained from low-mA QCT and the true values of the ESP. One-way ANOVA Tukey test was used to compare within-group differences in low-mA QCT measurements under different TAT conditions. The paired-sample t-test was used to compare the differences in BMD measurements for each vertebra between routine QCT and low-mA QCT. The root-mean-square errors(RMSEs) of the BMD measurements were calculated and compared;the correlation between RMSE and TAT was observed by Pearson correlation analysis. Results When TAT = 0 cm~2, 200 cm~2 and 320 cm~2, there were no statistically differences between routine QCT and low-mA QCT measurements(P>0.05), while TAT = 420 cm~2, significant differences were shown(P<0.05). TAT = 420 cm~2 group, the RMSEs using routine QCT were smaller than those using low-mA QCT. The RMSE of low-mA QCT was positively correlated with TAT;RMSEs of L1vertebrae were constantly larger than those of L2and L3vertebrae under different TAT conditions. Conclusion Low-mA QCT is a reliable method to measure lumbar BMD as accurately as routine QCT for the general population and has a great advantage in radiation dose, while for the overweight/obese people, routine QCT is more accurate.