Zhao Xia, Song Hee Kwon, Seifert Alan C, Li Cheng, Wehrli Felix W
Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, 1 Founders Building, MRI Education Center, Philadelphia, PA, United States of America.
PLoS One. 2017 Mar 15;12(3):e0173995. doi: 10.1371/journal.pone.0173995. eCollection 2017.
To develop and evaluate an integrated imaging protocol for bone water and phosphorus quantification in vivo by solid-state 1H and 31P MRI.
All studies were HIPAA-compliant and were performed with institutional review board approval and written informed consent. Proton (1H) ultra-short echo-time (UTE) and phosphorus (31P) zero echo-time (ZTE) sequences were designed and implemented on a 3 T clinical MR scanner to quantify bone water and mineral in vivo. The left tibia of ten healthy subjects (including both genders, 49±15 y/o) was examined with a custom-built 1H/31P dual-frequency extremity RF coil. Total bone water (TW), water bound to the collagen matrix (BW) and bone 31P were quantified from MR images with respect to reference samples of known 1H or 31P concentration, and pore water (PW) was subsequently determined from TW and BW. Porosity index (PI) was calculated as the ratio between UTE images acquired at two echo times. MRI parameters were compared with bone density measures obtained by high-resolution peripheral quantitative CT (HR-pQCT).
The total scan time for the bone water and 31P quantification protocol was about 50 minutes. Average TW, BW, PW and 31P concentrations were 13.99±1.26, 10.39±0.80, 3.34±1.41 mol/L and 7.06±1.53 mol/L for the studied cohort, respectively, in good agreement with previous results conducted ex vivo. Average intra-subject coefficients of variation were 3.47%, 2.60% and 7.50% for TW, BW and PW and 5.60% for 31P. Negative correlations were observed between PW and vBMD (p<0.05) as well as between PI and 31P (p<0.05), while bone mineral content (BMC) estimated from 31P MRI and HR-pQCT were strongly positively correlated (p<0.0001).
This work demonstrates the feasibility of quantifying bone water and mineral phosphorus in human subjects in a single MRI session with a clinically practical imaging protocol.
开发并评估一种通过固态氢质子（1H）和磷（31P）磁共振成像（MRI）对活体骨水和磷进行定量分析的综合成像方案。
所有研究均符合健康保险流通与责任法案（HIPAA）要求，并获得机构审查委员会批准及书面知情同意书。在一台3T临床磁共振扫描仪上设计并实施了质子（1H）超短回波时间（UTE）序列和磷（31P）零回波时间（ZTE）序列，以对活体骨水和矿物质进行定量分析。使用定制的1H/31P双频肢体射频线圈对10名健康受试者（包括男性和女性，年龄49±15岁）的左胫骨进行检查。根据已知1H或31P浓度的参考样本，从磁共振图像中对总骨水（TW）、与胶原基质结合的水（BW）和骨31P进行定量分析，随后根据TW和BW确定孔隙水（PW）。孔隙率指数（PI）计算为在两个回波时间采集的UTE图像之间的比率。将MRI参数与通过高分辨率外周定量CT（HR-pQCT）获得的骨密度测量值进行比较。
骨水和31P定量分析方案的总扫描时间约为50分钟。研究队列的平均TW、BW、PW和31P浓度分别为13.99±1.26、10.39±0.80、3.34±1.41mol/L和7.06±1.53mol/L，与先前的离体研究结果高度一致。TW、BW和PW的平均受试者内变异系数分别为3.47%、2.60%和7.50%，31P的平均受试者内变异系数为5.60%。观察到PW与体积骨密度（vBMD）之间以及PI与31P之间存在负相关（p<0.05），而通过31P MRI和HR-pQCT估计的骨矿物质含量（BMC）呈强正相关（p<0.0001）。
本研究表明，采用临床实用的成像方案，在单次MRI检查中对人体受试者的骨水和矿物质磷进行定量分析是可行的。
