Current status of imaging of articular cartilage

 Various imaging methods have been applied to assessment of articular cartilage. These include standard radiography, arthrography, CT, CT arthrography, ultrasonography, and MR imaging. Radiography remains the initial musculoskeletal imaging method. However, it is insensitive to early stages of cartilage abnormalities. MR imaging has great potential in the assessment of articular cartilage, although high-quality scans are required because imaging signs of cartilage abnormalities may be subtle. The potential and limitations of various sequences and techniques are discussed, including MR arthrography. The role of the other imaging methods in assessment of articular cartilage appears to be limited.     

Silicone rubber: an alternative for repair of articular cartilage defects

Silicone-rubber implants were used to fill full-thickness articular cartilage in the trochlea area of the knee joint in rabbits, for the purpose of studying the long-term influence of silicone-rubber implant on surrounding articular cartilage. Forty eight weeks after surgery, the silicone rubbers were still fitted tightly into the defects; surrounding cartilage showed mild degeneration, better than the control group. Our results showed silicone-rubber implantation for repairing local articular cartilage defects can effectively delay the pathogenetic progression of osteoarthritis.     

Sodium MRI of human articular cartilage in vivo

Preliminary results from in vivo sodium MRI of human patellar articular cartilage are presented. Sodium images generated of an in vitro bovine patella clearly distinguish the region of proteoglycan depletion from the region of healthy cartilage. This provides the first evidence that sodium imaging may be used to detect changes due to osteoarthritis in vivo. The process of optimizing imaging time and signal-to-noise ratio, as well as potential implications in the detection of osteoar-thritic change, are discussed.     

Quantitative MRI of articular cartilage and its clinical applications

Cartilage is one of the most essential tissues for healthy joint function and is compromised in degenerative and traumatic joint diseases. There have been tremendous advances during the past decade using quantitative MRI techniques as a noninvasive tool for evaluating cartilage, with a focus on assessing cartilage degeneration during osteoarthritis (OA). In this review, after a brief overview of cartilage composition and degeneration, we discuss techniques that grade and quantify morphologic changes as well as the techniques that quantify changes in the extracellular matrix. The basic principles, in vivo applications, advantages, and challenges for each technique are discussed. Recent studies using the OA Initiative (OAI) data are also summarized. Quantitative MRI provides noninvasive measures of cartilage degeneration at the earliest stages of joint degeneration, which is essential for efforts toward prevention and early intervention in OA. J. Magn. Reson. Imaging 2013;38:991–1008. © 2013 Wiley Periodicals, Inc.     

膝关节软骨MRI梯度回波序列的参数优化

目的：观察不同扫描参数对图像质量的影响，优化出不同的梯度回波序列的最佳扫描参数。方法：选择尸体膝关节2只，检查设备为Marconi eclipse 1．5T MR扫描仪。采用三维傅立叶稳态采集技术(3D FAST)；三维傅立叶稳态采集技术与脂肪抑制技术联合应用(FS 3D FAST)；三维射频毁损傅立叶稳态采集技术(3D FR-spoiled FAST，3D FR-spoiled FAST)；三维射频毁损傅立叶稳态采集技术与脂肪抑制序列联合应用(FS 3D FS-spoiled FAST)等4个序列进行扫描，每一序列采用不同的TE时间(5ms、10ms、15ms、20ms)结合不同翻转角(FLIP)(20、40、60)进行扫描(由于设备条件限制，3D FAST未进行，IE=5ms的扫描)。每一序列分别得到9组或12组不同成像参数的图像。分别计算不同序列、不同参数条件下的软骨与骨髓、软骨与液体的对比噪声比。数据采用SPSS软件包进行统计分析。结果：当，TE=10ms，FLIP=60时，FS 3D FAST序列及当，TE=5ms，FLIP=40时，FS 3D FR-spoiled FAST序列所得到软骨与骨髓及软骨与液体的对比噪声比均最佳。结论：①FS 3D RF-spoiled FAST序列的最佳扫描参数为，TE=5ms，FLIP=40；②FS 3D FAST序列的最佳扫描参数TE=10ms，FLIP=60。     

Fat suppressed MRI of articular cartilage with a spatial-spectral excitation pulse

We developed a three-dimensional, gradient-recalled-echo imaging technique that incorporates a short-duration spatial-spectral excitation pulse from the family of binomial pulses. Binomial pulses of different orders were tested on phantoms and on normal volunteers to find the composite pulse that produced in the shortest duration the most reliable fat suppression. Composite pulses employing unipolar slice-selective gradients with explicit rewinder gradients between each radiofrequency (RF) pulse were compared with composite RF pulses employing alternating-polarity, slice-select gradients. The advantage of the sequences using the unipolar gradients is improved fat suppression. Images of the knees of volunteers produced with the composite RF pulse have contrast between fat and articular cartilage equivalent to that on images created by the gradient-recalled-echo imaging technique employing a conventional chemsat pulse. The optimum RF pulse consisted of three amplitude- and phase-modulated pulses combined with unipolar slice-select gradients.     

Magnetic resonance imaging of articular cartilage: ex vivo study on normal cartilage correlated with magnetic resonance microscopy

The aims of this study were (a) to compare the MR appearance of normal articular cartilage in ex vivo MR imaging (MRI) and MR microscopy (MRM) images of disarticulated human femoral heads, (b) to evaluate by MRM the topographic variations in articular cartilage of disarticulated human femoral heads, and subsequently, (c) to compare MRM images with histology. Ten disarticulated femoral heads were examined. Magnetic resonance images were obtained using spin-echo (SE) and gradient-echo (GE) sequences. Microimages were acquired on cartilage–bone cylindrical plugs excised from four regions (superior, inferior, anterior, posterior) of one femoral head, using a modified SE sequence. Both MRI and MRM images were obtained before and after a 90 ° rotation of the specimen, around the axis perpendicular to the examined cartilage surface. Finally, MRM images were correlated with histology. A trilaminar appearance of articular cartilage was observed with MRI and with a greater detail with MRM. A good correlation between MRI and MRM features was demonstrated. Both MRI and MRM showed a loss of the trilaminar cartilage appearance after specimen rotation, with greater evidence on MRM images. Cartilage excised from the four regions of the femoral head showed a different thickness, being thickest in the samples excised from the superior site. The MRM technique confirms the trilaminar MRI appearance of human articular cartilage, showing good correlation with histology. The loss of the trilaminar appearance of articular cartilage induced by specimen rotation suggests that this feature is partially related to the collagen-fiber orientation within the different layers. The MRM technique also shows topographic variations in thickness of human articular cartilage. Received 28 July 1997; Revision received 31 December 1997; Accepted 6 January 1998     

应用磁共振生理学成像定量测定兔膝关节软骨退变的研究

目的：探讨磁共振生理学成像技术在检测关节软骨退变中的应用价值。方法：20只新西兰大白兔随机分为甲、乙、丙、丁四组。甲组左膝关节行常规磁共振成像后即刻处死,取股骨髁软骨行苏木素和伊红染色（hematoxylln and eosin,HE）、阿利辛兰染色（alcian blue,AB）及蛋白多糖含量测定。乙、丙、丁各组每只兔左膝关节内注射0．2na（10U）木瓜蛋白酶,并于注射前及注射后分别于24、48、72h先行相同常规磁共振成像及磁化传递对比成像（magnetization transfer contrast。MTC）,后行磁共振延迟增强软骨成像（delayed gadolimum enhanced MRI of cartilage,dGEMRIC）,测定关节软骨磁化传递率和L驰豫时间值。扫描结束后处死动物,取左膝股骨髁部软骨行大体观察、HE、AB染色及蛋白多糖含量测定。结果：注射木瓜蛋白酶后24、48h,蛋白多糖含量与甲组比较,统计学均有差异（P=0．048和0．045,P〈0．05）,注射后72h,统计学没有差异（P=0．455,P〉0．05）。注射木瓜蛋白酶后24、48、72h的T1弛豫率分别降低了316．09ms、244．01ms和143．98ms,注射后24、48h与注射前比较有统计学差异（P=0．047和0．045,P〈0．05）。注射木瓜蛋白酶前后相比,各组关节软骨磁化传递率不同程度地降低,但均没有统计学差异。结论：本研究采用的dGEMRIC、MTC成像技术能够通过定量检测T1弛豫时间值、磁化传递率反映软骨退变早期的生化改变。     

关节软骨MR成像进展

随着软骨序列的开发和应用，MRI对关节软骨的评价越来越重要。本文就关节软骨的MRI表现、关节软骨的MRI序列和扫描技术、关节软骨损伤以及修复术后MRI评价等方面进行了综述。     

Normal and degenerating articular cartilage: in vitro correlation of MR imaging and histologic findings.

Histologic correlation of the different magnetic resonance (MR) appearances of articular cartilage has not been studied extensively. Therefore, the authors correlated thin (high-resolution) MR sections of articular cartilage with histologic sections. Human cadaver lumbar facet joints were imaged with a 1-mm section thickness and a 4-cm field of view, then sectioned and stained for histologic comparison. MR imaging patterns were identified that correlated with normal cartilage and three histologically different patterns of degeneration.     

膝关节软骨磁共振T2弛豫时间测定在早期骨关节炎中的应用价值

目的:探讨关节软骨磁共振T2弛豫时间定量分析在早期膝关节骨关节炎(OA)中的应用价值。方法:运用T2mapping成像测量正常组(n=12)和平片没有阳性发现的早期OA组(n=15)膝关节胫骨内侧髁、外侧髁,股骨内侧髁、外侧髁和髌骨5处软骨的T2值,并进行统计学分析。结果:正常组膝关节软骨T2值33.8~35.6ms,早期OA组膝关节软骨T2值40.3~42.7ms。病例组膝关节各处软骨的T2值差异有显著性意义(P<0.01)。结论:T2弛豫时间定量分析可以发现没有形态学变化的OA关节软骨内成分变化,在早期OA诊断中有较高的应用价值。     

Comparison of 3D vs. 2D fast spin echo imaging for evaluation of articular cartilage in the knee on a 3T system scientific research

Purpose

We sought to retrospectively compare the accuracy of a three-dimensional fat-suppressed, fast spin-echo sequences acquired in the sagittal plane, with multiplanar reconstructions to that of two-dimensional fat-suppressed, fast spin echo sequences acquired in three planes on a 3 T MR system for the evaluation of articular cartilage in the knee.

Materials and methods

Our study group consisted of all patients (N = 34) that underwent 3 T MR imaging of the knee at our institution with subsequent arthroscopy over an 18-month period. There were 21 males and 13 females with an average age of 36 years. MR images were reviewed by 3 musculoskeletal radiologists, blinded to operative results. 3D and 2D sequences were reviewed at different sittings separated by 4 weeks to prevent bias. Six cartilage surfaces were evaluated both with MR imaging and arthroscopically with a modified Noyes scoring system and arthroscopic results were used as the gold standard. Sensitivity, specificity, and accuracy were calculated for each reader along with Fleiss Kappa assessment agreement between the readers. Accuracies for each articular surface were compared using a difference in proportions test with a 95% confidence interval and statistical significance was calculated using a Fisher's Exact Test.

Results

Two hundred and four articular surfaces were evaluated and 49 articular cartilage lesions were present at arthroscopy. For the patellofemoral surfaces, the sensitivity, specificity, and accuracy were 76.5%, 83%, and 78.2% for the 3D sequences and were 82.3%, 76%, and 82% respectively for the 2D sequences. For the medial compartment surfaces, the sensitivity, specificity, and accuracy were 81.1%, 65.1%, and 78.5% for the 3D sequences and were 82.5%, 48%, and 76.7% respectively for the 2D sequences. For the lateral compartment surfaces, the sensitivity, specificity, and accuracy were 89.3%, 39%, and 79.5% for the 3D sequences and were 94.7%, 18.8%, and 79.5% respectively for the 2D sequences. The accuracies were not significantly different between 3D and 2D sequences. Fleiss Kappa agreement values for the assessment of inter-observer agreement ranged from substantial for the patella and medial femur to moderate for the trochlea and fair for the medial tibia and lateral compartment.

Conclusion

There was no significant difference in accuracy for the evaluation of articular cartilage of a single three-dimensional, fast spin echo sequence with multi-planar reformatted images vs. two-dimensional, fast spin echo sequences acquired in all three imaging planes in the knee.     

Magnetic resonance imaging of intracranial atherosclerosis: Comparison of ex vivo 3T MRI and histologic findings

PurposeImaging the lipid-rich necrotic core (LRNC) is very important when evaluating the response of lipid-lowering therapy. The purpose of this study was to assess ex vivo LRNC of intracranial atherosclerosis using 3T MRI.Materials and methodsThirty-one atherosclerotic lesions from 17 specimens were analyzed (basilar artery = 15, middle cerebral artery = 16) using 3T MRI. Specimens were not chemically processed for imaging studies. Reconstructed MRI was matched with histologic sections at corresponding locations.ResultsThe median plaque thickness of intracranial atherosclerosis was 0.6 mm (0.4–2.0 mm). All specimens had a LRNC on histologic findings. Three specimens had plaque calcification on histologic findings. LRNC of 30 specimens (96.8%) appeared as homogeneous isointensity/hypointensity on T1-weighted imaging and hypointensity on T2-weighted imaging compared with T1-weighted imaging.ConclusionsAll specimens with ex vivo intracranial atherosclerosis had LRNC. Intracranial atherosclerosis could be an indication for lipid-lowering therapy, similar to previous carotid MR studies.     

Short-TE projection reconstruction MR microscopy in the evaluation of articular cartilage thickness

The aim of this study was to assess the potential of projection-reconstruction (PR) MR microscopy in the accurate measurement of cartilage thickness. Short-TE PR microimages were acquired at 7.05 T on bone-cartilage cylindrical plugs excised from four regions of two disarticulated femoral heads (i. e. superior, inferior, posterior and anterior), using an NMR instrument equipped with a microimaging accessory. The PR microimages were then correlated with conventional spin-echo (SE) microimages and with histology. On PR microimages, acquired with an echo time of 3.2 ms, the cartilage signal was increased, allowing an accurate delineation of the cartilage from the tidemark/cortical bone region. As a consequence, by the PR method a more precise measurement of cartilage thickness compared with that performed by the conventional SE approach was feasible. An excellent correlation between PR microimages and histology was also obtained (r = 0.90). By the proposed method it is possible to accurately determine the cartilage thickness better than with the conventional SE sequences. Received: 30 July 1999; Revised: 7 January 2000; Accepted: 14 March 2000     

正常青少年膝关节软骨的低场MRI表现

目的：探讨正常青少年膝关节软骨的MRI表现。方法：使用GE 0．2T低场磁共振成像机，采用膝关节线圈，对膝关节行矢状面扫描，应用序列为梯度回波序列T2WI、自旋回波T1WI、自旋回波T2WI、脂肪抑制序列、质子密度序列。翻转角200。扫描野16cm。层厚4mm，间隔1mm。结果：膝关节矢状位MRI梯度回波序列T2WI。和质子密度序列中，股骨髁与胫骨平台的骺软骨MRI能显示出3层不同的信号强度。结论：MRI能准确地显示膝关节软骨的层次结构，为临床诊断膝关节疾病提供参考依据。     

关节软骨病损的影像学诊断

目的 探讨慢性骨关节炎、类风湿性关节炎等几种慢性关节软骨损伤平片和MRI的诊断与鉴别诊断。方法 89例患者(骨关节炎61例，类风湿性关节炎9例，其他慢性损伤19例)共115个关节均行平片检查及MR T1WI、T2WI 质子密度加权像(PDWI)、短时反转恢复抑脂序列(STIR)、三维抑脂扰相梯度回波序列(3D FS SPGR)扫描，32例44个关节进行了增强扫描。其中90个膝关节的MRI分髌骨、股骨内髁、股骨外髁、胫骨4个关节面，按软骨病变Outerbridge分级法进行分析观察，61例75个关节进行了平片与MRI征象的对照观察。结果 MRI表现：关节软骨病变115个(100％)，同时伴有关节软骨变薄58个(50．4％)、软骨下骨质、骨髓改变22个(19．7％，)、滑膜增生52个(45．2％，)；类风湿性关节炎与骨关节炎组和其他慢性损伤组比较，类风湿性关节炎的软骨下骨质、骨髓改变的发生率与骨关节炎组及其他慢性损伤组差异有显著性意义(P值均=0．000)。把受累几率最大的髌软骨(81／90，90％)按MRI软骨病损Ⅰ～Ⅱ级为1组，Ⅲ～Ⅳ级为另1组，与平片的征象进行相关对照分析，两组间分别在平片的关节间隙狭窄(χ^2=9．349，P=0．002)、关节面下小囊变(χ^2=9．885，P=0．002)差异有非常显著性意义。结论Ⅰ～Ⅱ级软骨病变平片无恒定的征象，而Ⅲ～Ⅳ级软骨病变则可见关节间隙变窄与关节面下小囊变，主要与关节软骨病变及软骨下骨质改变相关：目前关节及关节软骨的影像学检查以X线平片结合MRI为最佳的检查方法，MR增强扫描有助于滑膜病变的诊断与鉴别诊断。     

磁共振T2-mapping成像对早期膝关节软骨损伤的诊断价值研究

目的：测量不同程度膝关节骨关节炎（osteoarthritis,OA）患者和正常对照组关节软骨的T2弛豫时间并比较其差异性,评价磁共振T2-mapping成像在早期膝关节软骨损伤中的应用价值。方法：采用GE signa 3.0T磁共振扫描系统T2-mapping成像测量OA组（n=78）和正常组（n=32）膝关节股骨内侧髁、外侧髁,胫骨内侧髁、外侧髁4处软骨的T2值,并进行统计学分析。结果：正常组、轻度OA组、重度OA组平均T2值分别为（38.36±2.45）ms（、49.28±4.24）ms、（53.12±5.36）ms,病例组与对照组关节软骨表面T2值有差异且具显著性统计学意义（P〈0.05）,轻度OA组和重度OA组之间差别无统计学意义（P〉0.05）。结论：T2-mapping成像可以发现没有形态学改变的关节软骨内组织成分的变化,对早期膝关节软骨损伤的诊断和监测具有很高的临床应用价值。     

定量磁共振对膝关节软骨的应用研究进展

膝关节软骨在维持关节正常运动中起着缓冲、减震及润滑的关键作用。软骨定量磁共振成像是一种比较新的磁共振成像技术,能够对软骨内的细微组织成分进行量化评估,是评价膝关节软骨及其病变的一种有效的影像学检查方法。本文对膝关节软骨的正常组织结构和定量磁共振在膝关节软骨的量化评估及临床应用予以综述。     

Accuracy evaluation of automatic quantification of the articular cartilage surface curvature from MRI

RATIONALE AND OBJECTIVES: To study the articular cartilage surface curvature determined automatically from magnetic resonance (MR) knee scans, evaluate accuracy of the curvature estimates on digital phantoms, and an evaluation of their potential as disease markers for different stages of osteoarthritis (OA). MATERIALS AND METHODS: Knee MR data were acquired using a low-field 0.18T scanner, along with posteroanterior x-rays for evaluation of radiographic signs of OA according to the Kellgren-Lawrence index (KL). Scans from a total of 114 knees from test subjects with KL 0-3, 59% females, ages 21-79 years were evaluated. The surface curvature for the medial tibial compartment was estimated automatically on a range of scales by two different methods: Euclidean shortening flow and boundary normal comparison on a cartilage shape model. The curvature estimates were normalized for joint size for intersubject comparisons. Digital phantoms were created to establish the accuracy of the curvature estimation methods. RESULTS: A comparison of the two curvature estimation methods to ground truth yielded absolute pairwise differences of 1.1%, and 4.8%, respectively. The interscan reproducibility for the two methods were 2.3% and 6.4% (mean coefficient of variation), respectively. The surface curvature was significantly higher in the OA population (KL > 0) compared with the healthy population (KLi = 0) for both curvature estimates, with P values of .000004 and .000006, respectively. The shape model based curvature estimate could also separate healthy from borderline OA (KL = 1) populations (P = .005). CONCLUSION: The phantom study showed that the shape model method was more accurate for a coarse-scale analysis, whereas the shortening flow estimated fine scales better. Both the fine- and the coarse-scale curvature estimates distinguished between healthy and OA populations, and the coarse-scale curvature could even distinguish between healthy and borderline OA populations. The highly significant differences between populations demonstrate the potential of cartilage curvature as a disease marker for OA.