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临床研究
压缩感知三维快速自旋回波序列诊断膝关节软骨损伤
王亚魁 金笑 袁慧书

Cite this article as: Wang YK, Jin X, Yuan HS. Three dimensional fast spin echo accelerated with compressed sensing diagnoses cartilage lesions in knee. Chin J Magn Reson Imaging, 2019, 10(5): 352-355.本文引用格式:王亚魁,金笑,袁慧书.压缩感知三维快速自旋回波序列诊断膝关节软骨损伤.磁共振成像,2019,10(5):352-355. DOI:10.12015/issn.1674-8034.2019.05.007.


[摘要] 目的 探讨压缩感知技术加速的三维快速自旋回波序列调制反转角成像技术(modulated flip angle technique in refocused imaging with extended echo train,MATRIX)在诊断膝关节软骨损伤中的应用价值。材料与方法 收集62例膝关节损伤的住院患者,同时行常规二维快速自旋回波(two dimensional fast spin echo,2D FSE)序列与MATRIX序列扫描。由2名放射科医师独立阅片,测量2D FSE与MATRIX图像软骨组织的信噪比(signal to noise ratio,SNR)及其与周围组织的对比噪声比(contrast to noise ratio,CNR),先后采用两种序列评估膝关节软骨损伤,以关节镜诊断结果为金标准,计算2D FSE与MATRIX序列诊断关节软骨损伤的敏感度、特异度及准确度。采用配对t检验比较两序列软骨SNR、CNR,McNemar检验比较两者软骨损伤诊断的差异。结果 在MATRIX序列图像中,软骨组织的SNR及其与周围组织的CNR均显著高于2D FSE序列(P<0.01)。MATRIX序列与常规2D FSE序列诊断膝关节软骨损伤的敏感度、特异度及准确度分别为70.8%/59.2%、75.5%/84.2%及74.1%/76.6%,二者诊断软骨损伤的敏感度及特异度有统计学差异(P<0.01),准确度无显著差异(P=0.067)。结论 与2D FSE序列相比,MATRIX序列图像中软骨具有较高的SNR与CNR,MATRIX序列诊断关节软骨损伤具有更高的敏感性,但是其特异度较低。
[Abstract] Objective: To explore the diagnostic performance of modulated flip angle technique in refocused imaging with extended echo train (MATRIX) which is a three dimensional fast spin echo accelerated with compressed sensing for cartilage lesions of the knee joint.Materials and Methods: Sixty-two knee joints in 62 patients with knee joint injury were examined at 3.0 T magnetic resonance imaging (MRI) system before arthroscopic operation. Following conventional two dimensional fast spin echo (2D FSE) protocol, MATRIX including sagittal fat-suppressed proton density weighted image (PDWI) and non-fat-suppressed T1-weighted image (T1WI) was performed. And then axial and coronal images were reformatted after MATRIX scanning. 2D FSE and MATRIX images were independently reviewed by two radiologists. Signal to noise ratio (SNR) and contrast to noise ratio (CNR) of cartilage in 2D FSE and MATRIX images were calculated. Two radiologists independently graded cartilage lesions according to ICRS grade system, and then sensitivity, specificity and accuracy of 2D FSE and MATRIX were calculated with arthroscopy as the reference standard. Statistic analysis was performed with paired t test and McNemar test.Results: SNR of cartilage and CNR of cartilage/fluid and cartilage/marrow in MATRIX were significantly higher (P<0.01) than these in conventional 2D FSE. The sensitivity, specificity and accuracy of MATRIX and 2D FSE for diagnosing cartilage lesions were respectively 70.8%/59.2%, 75.5%/84.2% and 74.1%/76.6%. MATRIX had significantly higher sensitivity (P<0.01) but lower specificity (P<0.01) than 2D FSE. There was no significant differences (P=0.067) in accuracy between two sequences.Conclusions: MATRIX has significantly higher SNR and CNR for cartilage, and provides higher sensitivity but lower specificity for diagnosing cartilage lesions compared to conventional 2D FSE.
[关键词] 软骨,关节;膝关节;磁共振成像
[Keywords] cartilage, articular;knee joint;magnetic resonance imaging

王亚魁 北京大学第三医院放射科,北京 100191

金笑 北京大学第三医院放射科,北京 100191

袁慧书* 北京大学第三医院放射科,北京 100191

通信作者:袁慧书,E-mail:huishuy@bjmu.edu.cn

利益冲突:无。


收稿日期:2018-11-21
接受日期:2019-03-19
中图分类号:R445.2; R684 
文献标识码:A
DOI: 10.12015/issn.1674-8034.2019.05.007
本文引用格式:王亚魁,金笑,袁慧书.压缩感知三维快速自旋回波序列诊断膝关节软骨损伤.磁共振成像,2019,10(5):352-355. DOI:10.12015/issn.1674-8034.2019.05.007.

       磁共振成像(magnetic resonance imaging,MRI)是目前诊断膝关节损伤的主要无创检查方式,临床中常规采用二维快速自旋回波(two dimensional fast spin echo,2D FSE)序列进行多平面成像,其诊断膝关节半月板及前交叉韧带(anterior cruciate ligament,ACL)损伤具有较高的准确性[1]。然而,由于2D FSE序列具有较大的层厚和层间距,在诊断软骨损伤中的表现较差,因而一些软骨特异的序列应用于膝关节软骨损伤的诊断,如T2-mapping、T1ρ及三维梯度回波序列[2,3,4],但是,在临床实践中这些序列往往需要与常规2D FSE序列相结合。三维快速自旋回波(three dimensional fast spin echo,3D FSE)具有连续薄层扫描及多平面重建的优势,在诊断膝关节软骨损伤中表现出更高的准确性[5,6],但是过长的扫描时间限制了其在临床的应用。最近,新的加速技术——压缩感知(compression sensing,CS)的应用,提高了3D序列的信号采集效率,成像时间甚至短于2D FSE的总体成像时间。但是,采用CS后的3D FSE对软骨损伤的诊断能力尚不明确。本研究目的在于评估CS加速后的3D FSE序列调制反转角成像技术(modulated flip angle technique in refocused imaging with extended echo train,MATRIX)诊断膝关节软骨损伤的价值。

1 材料与方法

1.1 研究对象

       研究通过了本院伦理委员会的审查,所有入组患者均需签署知情同意书。选取2018年2月至2018年6月本院运动医学科住院患者。纳入标准:(1)有明确膝关节创伤病史,需行常规MRI检查;(2)计划行关节镜检查或治疗。排除标准:(1)患有以下疾病者:类风湿性关节炎、化脓性关节炎、肿瘤、前交叉韧带粘液变性、关节纤维化;(2)既往有膝关节手术病史者;(3) MRI禁忌证:体内有金属(起搏器、义眼、金属植入物),妊娠期或幽闭恐惧症患者;(4)因各种原因MRI检查后未能行关节镜检查;(5) MRI检查与关节镜检查时间间隔超过1个月。

1.2 MR扫描方案

       MRI检查采用联影3.0 T磁共振成像仪uMR770(中国上海联影医疗科技有限公司),采用12通道相控阵膝关节线圈,行常规2D FSE序列和MATRIX序列成像。2D FSE序列包括:轴位、冠状位、矢状位脂肪抑制质子密度加权像(fat-suppressed proton density weighted image,FS PDWI)及矢状位非脂肪抑制T1加权像(non-fat-suppressed T1-weighted image,NFS T1WI)。MATRIX序列扫描包括:矢状位脂肪抑制PDWI及非脂肪抑制T1WI (表1),后处理行轴位、冠状位薄层(层厚0.8 mm)重建。

表1  磁共振成像序列参数
Tab. 1  Parameters of magnetic resonance imaging sequences

1.3 关节镜

       关节镜手术由本院运动医学中心进行,关节镜下软骨损伤分级采用国际软骨修复协会(International Cartilage Regeneration & Joint Preservation Society,ICRS)分级标准[7]:0度,正常;Ⅰ度,表面损伤,表面软化不平或表浅的缺损、裂隙;Ⅱ度,损伤范围≤50%软骨厚度;Ⅲ度,损伤范围>50%软骨厚度,但是未达软骨下骨;Ⅳ度,软骨损伤达软骨下骨。

1.4 图像分析

       图像分析包括测量图像信噪比(signal to ratio,SNR)、对比噪声比(contrast to noise ratio,CNR),计算两序列诊断软骨损伤的敏感度、特异度及准确度。由2名放射科医师独立阅片,最终结果为2名医师测量结果的平均值。2D FSE与MATRIX序列阅片在同一台显示器进行,两次软骨损伤诊断时间间隔不少于3周,阅片时医师对患者临床病史、症状、体征均未知。

       SNR计算方式参照美国电器制造商协会(Nation Electrical Manufactures Association,NEMA)技术标准[8,9]。感兴趣区(region of interest,ROI)在矢状位图像上选取,测量的部位包括:关节液、髌软骨、软骨下骨,取相应组织的无损伤、信号均匀区域,两序列图像基本在相对应的层面选取ROI。组织信号强度(S组织)为ROI内的平均信号强度,图像噪声(noise)为图像背景四个角区域信号标准差的平均值(SD平均)与校正因子f的商,即噪声:,其中校正因子f为0.66,计算公式:信噪比,对比噪声比

       MRI关节软骨损伤分级采用ICRS分级系统:0度,正常,软骨表面光滑,内部信号均匀;Ⅰ度,仅表现为软骨信号异常或表面不平,无明确软骨缺损;Ⅱ度,软骨缺损,深度小于或等于软骨厚度50%;Ⅲ度,软骨缺损,深度大于软骨厚度50%,但未达软骨下骨;Ⅳ度,软骨全层缺损,暴露软骨下骨。所有的关节面分为6个部分:髌骨、滑车、股骨内侧髁、股骨外侧髁、胫骨内侧平台、胫骨外侧平台,对于同一关节面软骨有多处损伤者,以分级较高的损伤为准。对于2名医师诊断结果不一致的病例,保留2名医师结果,最终计算2名医师诊断率值的平均值。

1.5 统计方法

       统计分析采用SPSS 20.0统计软件。MATRIX与2D FSE图像SNR、CNR为2名医师测量结果的平均值,采用配对t检验比较两序列差异。以关节镜结果为金标准,计算2D FSE与MATRIX序列诊断软骨损伤的敏感度、特异度和准确度。采用McNemar检验分析两序列诊断的差异。P<0.05表示差异有统计学意义。

2 结果

       共有66例膝关节符合纳入标准,其中3例因未行关节镜手术,1例患者因既往有膝关节术史而被排除,最终共有62例(男39例,女23例)纳入分析,平均年龄(36.7±15.0)岁,最大65岁,最小13岁,所有纳入分析的病例关节镜手术与MRI检查时间间隔均未超过4 d。

       MATRIX序列图像的液体、软骨及软骨下骨髓的SNR均显著高于2D FSE序列,关节软骨相对于液体及骨髓的CNR亦显著高于2D FSE序列(表2)。

       62例膝关节共372个关节面软骨,关节镜下共有113例软骨损伤,与常规2D FSE序列相比,MATRIX序列诊断软骨损伤的具有更高的敏感度,但是特异度较低(表3)。并且,MATRIX序列对于显示较小的软骨损伤(Ⅰ~Ⅱ度)更为敏感(图1),另外,对于部分软骨表面完整、关节镜诊断正常的软骨,MATRIX能够显示其内部信号的变化(图2)。

图1  患者男,49岁。内侧胫骨平台软骨,关节镜诊断Ⅰ度损伤。A:2D FSE FS PDWI示内侧胫骨平台软骨无明显异常信号;B:MATRIX FS PDWI可见内侧胫骨平台软骨点状高信号(箭)
图2  患者女,63岁,外侧胫骨平台关节软骨,关节镜未见软骨损伤。A:2D FSE FS PDWI矢状位箭头所示外侧胫骨平台软骨无明显信号改变;B:MATRIX FS PDWI矢状位,在相应位置可见软骨内部点状高信号(箭)
Fig. 1  Medial tibial plateau cartilage of a 49-year-old male confirmed grade Ⅰ cartilage lesion by arthroscope. A: 2D FSE FS PDWI shows a normal cartilage without any abnormal signal. B: MATRIX FS PDWI shows punctiform increased signal in the cattilage (arrow).
Fig. 2  Lateral tibial plateau cartilage of a 63-year-old female confirmed normal cartilage by arthroscope. A: 2D FSE FS PDWI does not show any abnormal signal in the cartilage. B: MATRIX FS PDWI shows punctiform increased signal in the cattilage (arrow).
表2  MATRIX与2D FSE图像SNR、CNR比较
Tab. 2  Comparison of SNR and CNR between MATRIX and 2D FSE
表3  两名放射科医师采用2D FSE与MATRIX序列诊断膝关节软骨损伤的敏感度、特异度及准确度[%,(例)]
Tab. 3  Sensitivity, specificity, and accuracy of 2D FSE and 3D MATIRX in detection of cartilage lesions for both doctors combined [%,(n)]

3 讨论

3.1 MATRIX序列特点

       MATRIX是基于可变翻转角技术的3D FSE序列,具有薄层连续扫描、可多平面重建的优点。另外为了减少成像时间,MATRIX采用了CS加速技术。CS是一种新的加速信号采集的技术,在MRI成像中CS采取稀疏采样方式,降低K空间样本量,然后通过非线性迭代算法无失真重构图像,目前CS已经应用于多种MRI技术[10,11]。笔者采用的MATRIX序列3.7倍的加速因子使压脂PDWI图像的成像时间只需约5 min (表1),基本满足了临床应用的需求。

3.2 MATRIX序列显示软骨及诊断软骨损伤的表现

       本研究表明MATRIX图像中软骨具有更高的SNR,且软骨与周围液体、软骨下骨CNR更高。之前一些学者采用其他3D FSE序列(3D SPACE)的得出相似的结论[12],另外,最近Kijowski等[13]对CS加速前后的3D FSE序列(FSE-Cube)图像质量进行比较,结果表明CS的应用并没有明显降低FSE-Cube图像的SNR。理论上更高的SNR与CNR更有利于显示软骨损伤区信号的变化。

       在之前的研究中,Kijowski等[14]比较了FSE-Cube与常规2D FSE序列诊断膝关节软骨损伤的差异,FSE-Cube表现出更高的敏感度与较低的特异度,而Ai等[5]的研究中FSE-Cube诊断软骨损伤的敏感度及特异度均显著高于2D FSE序列。另外,其他的一些研究结果显示虽然二者诊断软骨损伤的敏感度及特异度没有显著差异,但是3D序列的敏感度均具有更高的趋势[6,12]。我们的结果与之前的研究相似,与常规2D FSE序列相比,CS加速后的MATRIX诊断关节软骨损伤具有更高的敏感度,尤其是Ⅰ~Ⅱ度损伤(表3),其主要原因在于薄层图像具有更高的空间分辨率,降低了部分容积效应的影响,有利于更小的软骨损伤的显示(图1)。另外,MATRIX更高的对比噪声比,也有利于提高损伤软骨与正常软骨的对比度。与2D FSE序列相比,MATRIX诊断软骨损伤特异度较低,其主要原因在于MATRIX序列层面内的分辨率较低,而且有研究表明CS的应用会增加图像的模糊效应[13],这些因素可能使软骨表面信号不均匀。另外,关节镜难以观察到软骨内部的损伤,而三维薄层磁共振成像对软骨内部信号的改变较为敏感(图2),也是MATRIX序列特异度较低的原因之一。

3.3 总结

       与既往研究相比,我们的研究的意义在于采用了新的加速技术,减少了3D FSE序列的成像时间。本研究结果表明,与常规2D FSE序列相比,CS加速的MATRIX序列图像软骨具有更高的SNR与CNR,MATRIX诊断关节软骨损伤具有更高的敏感度,尤其是对Ⅰ~Ⅱ度损伤的识别,但是其诊断软骨损伤的特异度较低。

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