7.0 TMR关节软骨自旋锁定三维自旋-晶格弛豫时间成像与量化分析的实验研究

摘要

目的 建立MR关节软骨自旋锁定旋转坐标系中的自旋-晶格弛豫时间(T1ρ)三维成像技术和量化分析方法.方法 用7.0 T MR机和内径为6 cm的圆柱形鸟笼23Na-H射频线罔,采用自旋锁定自动补偿脉冲簇和三维自旋回波序列,自旋锁定时间(spin-locking time,TSL)分别为0、10、20、30、40和50 ms,自旋锁定频率带宽为440 Hz(自旋锁定磁场BsL),对6个不同浓度(1%～6%)琼脂糖凝胶体模和8个猪髌骨分别进行自旋锁定T1ρ成像扫描,建立自旋锁定T1ρ成像技术并评价其重复性.在Vnmr J图像终端上,利用自行编制的软件进行三维重组自旋锁定T1ρWI,并重构T1ρ弛豫时间图;采用人工标注的方法画感兴趣区,分别测定体模与髌骨软骨T1ρWI的信噪比(SNR)与T1ρ值.T1ρ值在各组间的对比,行单因素方差分析;软骨组织与琼脂糖体模SNR随时间对比关系的假设检验,行多因素方差分析.结果 关节软骨T1ρWI的SNR值、短自旋锁定时间采集图像的SNR值明显高于长自旋锁定时间采集的图像.在不同自旋锁定时间髌骨软骨T1ρWI,SNR值在48 4±8～95±8之间;不同自旋锁定时间,正常软骨SNR与1%琼脂糖体模的对比关系不同,当自旋锁定时间＜30 ms时,琼脂糖体模的图像SNR均低于正常软骨;＞30 ms时,正常软骨的图像SNR均低于1%的琼脂糖体模.随着琼脂糖浓度减少,不同自旋锁定时间采集的图像SNR值逐渐增加.各浓度琼脂糖凝胶体模T1ρ值测量的变异系数均小于10%,显示重复性好.髌骨关节软骨全层、表层、中间层、深层、钙化层T1ρ值测定结果分别为(68.9±6.3)、(80.7±12.8)、(65.7±7.0)、(82.4±7.7)、(69.7±6.4)ms(F=6.436,P＜0.05).T1ρ值在软骨表层和深层明显高于中间层、钙化层和软骨全层.结论 三维自旋锁定T1ρ成像技术是可行的、敏感的、特异的软骨分子成像技术,T1ρ弛豫时间图可量化测量关节软骨的分层状结构.%Objectlve To demonstrate the feasibility of three-dimensional(3D)spin-lattice relaxation time in the rotating frame(T1ρ)-weighted imaging of porcine patellar cartilage in vitro at 7.0 T and the measurement of T1ρ of agarose phantom and patellar cartilage.Methods All the MR Imaging experiments were performed on a 7.0 T Varian scanner using a 6.0-cm-diameter quadrature birdcage RF coil tuned to 300 MHz.A 3D spin-echo sequence with a self.compensating spin-lock pulse cluster was used to acquire 3D-T1ρ-weighted images.The time of spin-locking(TSL)was from 0 to 50 ms with an interval of 10 ms.Spin-lock power wag 440 Hz.3D-T1ρweighted imaging was done three times for 6 phantoms (concentration 1%t0 6%),as well as once for 8 porcine patellar cartilages in order to assess the reproducibility of this technique.Signal-to-noise ratio(SNR)was measured on the acquired images of both phantoms and patellar cartilages,which were tested for significance using Two-way ANOVA.The images were processed on Vnmr J workstation using home-built processing software to construct 3 D T1ρ maps.T1ρ values were calculated within manually drawn regions-of-interest(ROI),and differences between groups were tested for significance using analysis of variance(One-way ANOVA).Results T1ρ -weighted images with a shorter TSL had a higher SNR value,which measured between 48±8 and 95±8 in the global cartilage.Cartilage images had a higher SNR(TSL＜30 ms)compared to agarose phantoms and a lower SNR(TSL ＞30 ms)only compared to l%agarose phantorm T1ρ relaxation times in agarose phantoms increased as agarose concentrations decreased in global regions.The CV of T1ρ in agarose phantoms was less than 10%.Global and regional analyses of patellar cartilage T1ρ were 68.9±6.3 ms,80.7±12.8 ms,65.7±7.0 ms,82.4±7.7 ms,and 69.7±6.4 ms in the global cartilage,the superficial layer,the transitional layer,the deep layer,and the calcified layer,respectively.T1ρ in the superficial and deep layer was significantly higher than in the transitional,calcified layer and global cartilage(F=6.436,P＜0.05).Conclusions The present study demonstrates the feasibihty of 3D-T1ρ-weighted imaging of porcine patellar cartilage at 7.0 T with hish image quality.T1ρ maps can be used to quantify the laminar structures in 3D-T1ρ-weighted images of articular cartilage,which pave the way to evaluate early osteoarthritis and cartilage regeneration.