Advanced magnetic resonance imaging of articular cartilage

MRI is one of the most accurate imaging methods available to diagnose disorders of articular cartilage. Conventional two-dimensional and three-dimensional approaches show changes in cartilage morphology. Newer and substantially faster three-dimensional imaging methods show great promise to improve MRI of cartilage. These methods may allow acquisition of fluid-sensitive isotropic data that can be reformatted into arbitrary planes for improved detection and visualization of pathology. Unique MRI contrast mechanisms also allow clinicians to probe cartilage physiology and detect early changes in cartilage macromolecules.     

关节软骨磁共振生理性成像临床应用

关节软骨主要由软骨细胞和细胞外基质组成,软骨基质构建了稳定而复杂的耐压框架结构.关节软骨磁共振生理性成像是评价关节软骨基质成分变化的新型影像学技术.按照观察对象不同,可将其分为蛋白多糖相关技术(延迟动态增强、T1ρ成像和Na谱成像)、胶原含量相关技术(T2地图成像和磁化转移成像)、软骨基质内水含量相关技术(质子密度地图成像和弥散加权成像).延迟动态增强和T2地图成像已开始应用于软骨病变的早期诊断和治疗评价中.随着磁共振设备和分析软件的不断进步,关节软骨磁共振生理性成像将成为骨关节影像研究的重点之一.     

Quantitation of articular cartilage using magnetic resonance imaging and three-dimensional reconstruction

A quadrature knee coil was used in conjunction with a magnetic resonance imaging scanner for quantitation of test phantom volumes, ex vivo bovine cartilage thickness, and in vivo human articular cartilage volumes. Optimal magnetic resonance parameters were obtained by testing a series of spin-echo and gradient-echo pulse sequences to determine the sequence that provided the highest resolution of articular cartilage and best defined the cartilage interfaces with synovial fluid and subchondral bone. Extensive testing revealed that two sequences were required to define articular cartilage accurately: a spoiled gradient-echo sequence and a steady state free-precession sequence. Three-dimensional reconstruction and statistical analyses of test phantoms and of bovine and human cartilage images were performed. Differences between actual phantom volumes and three-dimensional measurements demonstrated that, as magnetic resonance slice thickness was increased, the measurement variability also increased (coefficient of variation ranging from 1.7 ± 1.3% for 1.0 mm slice thickness to 22.7 ± 1.9% for 3.0 mm slice thickness). When the phantom volume was greater than 1,800 mm³, the intraobserver, interobserver and interscan accuracies were greater than 97, 98, and 96%, respectively. This high degree of reproducibility pertained for the data on in vivo human cartilage data also. For experienced observers, the intraobserver and interobserver reproducibility were greater than 98 and 97%, respectively. The interscan reproducibility was greater than 98%. These data demonstrate that improved magnetic resonance pulse sequencing, in conjunction with three-dimensional reconstruction and measurement techniques, can accurately and reproducibly measure the volume of articular cartilage. Clinical application of this approach offers the potential for early diagnosis of osteoarthritis and for serial, noninvasive assessment of changes in articular cartilage volume in response to therapeutic modalities.     

磁共振技术评估膝关节软骨退变研究进展

磁共振成像(magnetic resonance imaging,MRI)扫描序列及参数的合理选择对清晰成像及临床研究结果的客观评价至关重要。全膝关节磁共振成像积分,波士顿利兹骨关节炎评分系统,MRI膝骨关节炎评分系统,膝骨关节炎软骨修复评分系统等全膝关节的半定量评分系统都能够全面评价膝骨关节炎进展时各组织的影像学改变。随着MRI技术的不断发展,关节软骨的形态学及生理成分的改变可以被定量评估。T2图、弥散加权成像、延迟动态增强成像等软骨成分的定量评估技术能定量监测软骨基质成分的变化,可以在关节软骨形态学破坏之前更早地发现软骨病变。这些定量、半定量评价技术有助于膝骨关节炎的早期诊断和早期预防,同时也为精确评价干预措施的疗效提供了可能。     

Proposal for a nomenclature for magnetic resonance imaging based measures of articular cartilage in osteoarthritis

OBJECTIVE: Magnetic resonance imaging (MRI) of articular cartilage has evolved to be an important tool in research on cartilage (patho)physiology and osteoarthritis (OA). MRI provides a wealth of novel and quantitative information, but there exists no commonly accepted terminology for reporting these metrics. The objective of this initiative was to propose a nomenclature for definitions and names to be used in scientific communications and to give recommendations as to which minimal methodological information should be provided when reporting MRI-based measures of articular cartilage in OA. METHODS: An international group of experts with direct experience in MRI measurement of cartilage morphology or composition reviewed the existing literature. Through an iterative process that included a meeting with a larger group of scientists and clinicians (December 2nd, 2004, Chicago, IL, USA), they discussed, refined, and proposed a nomenclature for MRI-based measures of articular cartilage in OA. RESULTS: The group proposes a nomenclature that describes: (1) the anatomical location and (2) the structural feature being measured, each name consisting of a metric variable combined with a tissue label. In addition, the group recommends minimal methodological information that should be described. CONCLUSIONS: Utilization of this nomenclature should facilitate communication within the scientific community. Further, the uniform adoption of comprehensive nomenclature to describe quantitative MRI- features of articular cartilage should strengthen epidemiological, clinical, and pharmacological studies in OA.     

Magnetic resonance imaging of articular cartilage of the knee

Recently developed magnetic resonance (MR) imaging techniques allow accurate detection of moderate- and high-grade articular cartilage defects. There has been increased interest in MR imaging of articular cartilage in part because it is useful in identifying patients who may benefit from new articular cartilage replacement therapies, including chondrocyte transplantation, improved techniques for osteochondral transplantation, chondroprotective agents, and cartilage growth stimulation factors. The modality also has the potential to play an important role in the follow-up of patients during and after treatment. Detection of articular cartilage defects is beneficial for patients undergoing arthroscopy for other injuries, such as meniscal tears, because the presence of articular cartilage injury worsens prognosis and may modify therapy options.     

Water distribution patterns inside bovine articular cartilage as visualized by 1H magnetic resonance imaging

OBJECTIVE: To develop a magnetic resonance imaging (MRI) technique to non-invasively map water volume fraction (WVF) in articular cartilage. Special emphasis was placed on spatial resolution and temporal considerations, aimed at creating a procedure feasible for eventual human studies. DESIGN: Absolute proton density MR images of intact, ex vivo bovine patellae were calculated from fully T(1) relaxed, short echo time images. This was accomplished through compensation for T(2) decay with calculated T(2) maps. Calibration of the signal intensity in the image was accomplished with the use of H2O:D2O phantoms, where the WVF was varied from 0.95 to 0.75. Application of the calibration curve to the entire image yielded images that represent WVF on a pixel by pixel basis. Calculations of water content by weight were performed by considering the density of the solid content. RESULTS: Using four echo time points, experiments comparing MR images from single-echo and multi-echo spin echo sequences yielded similar results. T(2) decreased with depth through the cartilage, with a maximum at the articular surface of approx 100 ms, and a approximately 50 ms minimum at the bone/cartilage interface. The WVF through the depth of the cartilage showed a similar trend, decreasing from 0.9 at the surface, to 0.7 at the bone/cartilage interface. Translation to a weight percent yielded approximately 86% weight at the surface, trending down to approximately 63% at the bone/cartilage interface, with an average of 74.5% for five patellae. These MRI derived values were compared to the measured weight of water in excised cartilage plugs from the same patellae and showed remarkably close agreement. CONCLUSION: We have demonstrated that MRI can non-invasively map WVF in cartilage in a pixel by pixel manner. This was accomplished in a time span that was clinically feasible, allowing the routine use of this method in a clinical setting. Moreover, this procedure employed standard MRI equipment and pulse sequences, avoiding the need for hardware modifications and using simple post processing methods. However, baseline studies need to be performed prior to incorporation into a standard radiological evaluation. Implications in the diagnosis of osteoarthritis (OA) are discussed.     

Structural periodicity in human articular cartilage: comparison between magnetic resonance imaging and histological findings.

OBJECTIVE: To relate the vertical striations visualized in the deeper layers of articular cartilage by Magnetic Resonance Imaging (MRI) to histological features. METHODS: Two knee joints recovered at post-mortem from males in their seventies with no history or visual evidence of joint disease were examined. MR images were obtained in a 4.7 T 400 mm-bore magnet, after which the knees were fixed, sectioned, and examined histologically. RESULTS: High resolution MR showed vertical high/low signal striations with a two to three-fold variation in signal intensity and a periodicity of 0.56 (+/-0.16 mm), most prominent in weight bearing areas. Histological sections revealed alternating light and dark staining areas with a periodicity of 1.01+/-0.54 mm in the lower zones of the cartilage, some, but not all of which clearly represented folding. Given that MR will only visualize vertical structures in cartilage aligned at 90 degrees, whereas histology will cut them at varying angles, it is likely that the vertical structures seen by each modality correspond, and that they represent structural heterogeneity in cartilage; perhaps the presence of plates of high collagen and proteoglycan content. CONCLUSION: The vertical striations seen routinely in the deep zones of hyaline articular cartilage on histological sections are not artefactual; they are likely to represent structural heterogeneity due to the presence of areas of high collagen and high proteoglycan content that exist in weight-bearing areas. This structural heterogeneity may be of great importance to the integrity and function of the cartilage.     

磁共振T2弛豫时间图成像技术在关节软骨中的应用

磁共振成像可无创显示关节软骨,对关节软骨细胞外基质的生化及力学方面的早期变化具有很高的敏感度。关节软骨的磁共振T_2弛豫时间值与软骨的含水量、胶原结构、生物力学因素有关,T_2弛豫时间图成像技术是目前应用最为广泛的磁共振成像技术之一,通过测量软骨磁共振脉冲序列不同回波时间像的信号强度变化得到T_2值。作为评估关节软骨早期病变的敏感影像参数之一,T_2伪彩图及其T_2值可用于评价软骨形态学和功能学,有助于了解骨关节炎、软骨老化和运动后的生理及病理变化,并可用于评估软骨病变早期诊断及修复评估。该文就T_2弛豫时间图成像技术的基本原理、影响因素和临床应用现状作一综述。     

Advances in articular cartilage repair

Many joint and systemic disorders may lead to cartilage defects. Partial thickness defects of the articular cartilage do not have healing potential. When the lesion reaches the subchondral bone, spontaneous healing may be observed, but consists of fibrocartilaginous tissue. The main efforts for cartilage repair are targeted at filling of the cartilage defect with a tissue that possesses the same mechanical properties with hyaline cartilage and the consolidation of this tissue with the native articular cartilage. There are various arthroscopic techniques and although they provide pain relief, they do not restore the damaged cartilage. Osteochondral transplantation is more effective in dealing with small or medium size full thickness defects, but further efforts are required in order to reduce the donor site morbidity, marginal necrosis and partial covering of the defect.     

Detection of changes in articular cartilage proteoglycan by T(1rho) magnetic resonance imaging.

The purpose of this work is to demonstrate the feasibility of T(1rho)-weighted magnetic resonance imaging (MRI) to quantitatively measure changes in proteoglycan content in cartilage. The T(1rho) MRI technique was implemented in an in vivo porcine animal model with rapidly induced cytokine-mediated cartilage degeneration. Six pigs were given an intra-articular injection of recombinant porcine interleukin-1beta (IL-1beta) into the knee joint before imaging to induce changes in cartilage via matrix metalloproteinase (MMP) induction. The induction of MMPs by IL-1 was used since it has been extensively studied in many systems and is known to create conditions that mimic in part characteristics similar to those of osteoarthritis. The contralateral knee joint was given a saline injection to serve as an internal control. T(1rho)-weighted MRI was performed on a 4 T whole-body clinical scanner employing a 2D fast spin-echo-based T(1rho) imaging sequence. T(1rho) relaxation parameter maps were computed from the T(1rho)-weighted image series. The average T(1rho) relaxation rate, R(1rho) (1/T(1rho)) of the IL-1beta-treated patellae was measured to be on average 25% lower than that of saline-injected patellae indicating a loss of proteoglycan. There was an average reduction of 49% in fixed charge density, measured via sodium MRI, of the IL-1beta-treated patellae relative to control corroborating the loss of proteoglycan. The effects of IL-1beta, primarily loss of PG, were confirmed by histological and immunochemical findings. The results from this study demonstrate that R(1rho) is able to track proteoglycan content in vivo.     

骨性关节炎患者膝关节软骨损伤的关节镜与MRI诊断分级研究

[目的]提出关节镜及核磁共振成像(magnetic resonance imaging,MRI)诊断骨性关节炎(osteoarthrisis,OA)患者膝关节软骨损伤的分级法,探讨MRI在诊断关节软骨损伤中的价值。[方法]回顾性分析行关节镜检查的123例骨性关节炎患者的膝关节术前MRI表现;按部位将膝关节软骨分为6处;根据形态和信号改变,结合损伤部位,将膝关节软骨损伤在关节镜与MRI的表现加以分析并分级;以关节镜所见为参考标准,计算MRI诊断各级软骨损伤的敏感性、特异性、准确性。[结果]在关节镜及MRI上,膝关节软骨损伤均可分为Ⅰ~Ⅳ级;在738处软骨中,损伤505处(68.43%),其中髌股关节最多,外侧胫股关节最少,且损伤以Ⅲ~Ⅳ级为主;关节镜与MRI判断软骨损伤差异具有统计学意义(χ~2=107.52,P<0.001)。MRI诊断软骨损伤总的敏感性、特异性、准确性分别为70.10%、93.13%、77.37%。[结论]骨性关节炎患者膝关节软骨损伤在关节镜及MRI的表现可被分为4级;软骨损伤以髌股关节最多;MRI诊断骨性关节炎软骨损伤的特异性较高,但敏感性和准确性相对较低。     

关节软骨缺损的治疗进展

完整的关节软骨是关节行使正常功能的基础 ,但关节软骨极其脆弱且自身修复能力低下 ,病损关节往往表现为不可扼制的逐步恶化 ,最终导致骨关节炎 (ｏｓｔｅｏａｒｔｈｒｉｔｉｓ,ＯＡ)的发生和关节功能的丧失 ,这种情况在负重的髋、膝等大关节尤其常见。本文着重介绍国内外现有关节软骨缺损的治疗方法、疗效评价及相关研究动态。1　关节镜灌洗术和关节清理术这是一种最基本的传统治疗手段。Ｊａｃｋｓｏｎ等对膝关节疾患患者行诊断性关节镜检术时发现 ,通过关节腔灌洗 ,45 %的患者疼痛症状明显缓解 ,疗效可维持 3 5年 ,只有 2 0 %的患者无效 …     

Diffraction-enhanced X-ray imaging of articular cartilage

OBJECTIVE: To introduce a novel X-ray technology, diffraction-enhanced X-ray imaging (DEI), in its early stages of development, for the imaging of articular cartilage. DESIGN: Disarticulated and/or intact human knee and talocrural joints displaying both undegenerated and degenerated articular cartilage were imaged with DEI. A series of three silicon crystals were used to produce a highly collimated monochromatic X-ray beam to achieve scatter-rejection at the microradian level. The third crystal (analyser) was set at different angles resulting in images displaying different characteristics. Once the diffraction enhanced (DE) images were obtained, they were compared to gross and histological examination. RESULTS: Articular cartilage in both disarticulated and intact joints could be visualized through DEI. For each specimen, DE images were reflective of their gross and histological appearance. For each different angle of the analyser crystal, there was a slight difference in appearance in the specimen image, with certain characteristics changing in their contrast intensity as the analyser angle changed. CONCLUSIONS: DEI is capable of imaging articular cartilage in disarticulated, as well as in intact joints. Gross cartilage defects, even at early stages of development, can be visualized due to a combination of high spatial resolution and detection of X-ray refraction, extinction and absorption patterns. Furthermore, DE images displaying contrast heterogeneities indicative of cartilage degeneration correspond to the degeneration detected by gross and histological examination.     

壳聚糖在关节软骨组织工程中应用的研究进展

关节软骨一旦被损伤，因其缺乏自身血液循环系统，仅靠关节滑液提供大部分营养。随着年龄的增长，软骨细胞的合成能力下降，故关节软骨损伤后很难修复。虽然40多年来许多修复技术被广泛应用，但是至今还没有一种方法可以让受损软骨持续再生，从而达到完全修复的目的。组织工程的兴起在软骨的再生以及受损软骨的治疗方面显示出巨大的潜力。支架材料作为人工细胞外基质承载种子细胞是组织工程研究的重要内容之一。近年来，以壳聚糖为支架的材料及其在矫形组织工程中的应用正受到越来越多的关注。壳聚糖是一种理想的高分子生物材料，它具有机体反应小、天然抗菌性以及具有可任意塑性如多孔结构的特点，使其能够适合细胞的内在生长以及骨的传导，在组织工程中显示出巨大的应用价值。     

Detection of articular defects using magnetic resonance imaging: an experimental study

This study evaluates magnetic resonance imaging (MRI) in the detection of surgically created articular defects in bovine knees. A total of 26 articular defects was created in 2 fresh cadaveric cows' knees. The defects created include chondromalacic grade 2 defects, chondral and osteochondral defects from 3 to 15 mm in diameter. The knee joints were repaired in a normal saline bath to exclude air in the joint prior to MR scanning. T1 weighted spin echo (SE) images and 3D gradient echo (FISP 40 degrees 3D) images were obtained. The T1 weighted SE imaging technique detected 15 defects (57.7%) compared with FISP 3D imaging technique detection of 17 defects (65.4%). The two techniques combined enable 21 of 26 defects (80.8%) to be detected. The imaging techniques used in this study were not able to detect chondromalacic defects less than 10 mm in diameter, nor chondral defects less than 5 mm in diameter. However, small osteochondral defects of 3 mm in diameter are detectable provided the depth of the defect is not less than 10 mm. The FISP 3D imaging technique alone is more sensitive in detecting chondral defects. Both imaging techniques have similarly high sensitivities in detecting osteochondral defects. The imaging time for combined T1 weighted SE and FISP 3D sequence is short (16.5 mm) and this combined technique may be useful for MR scanning of knee joints suspected to have articular defects.     

Monitoring glycosaminoglycan replenishment in cartilage explants with gadolinium-enhanced magnetic resonance imaging.

We previously devised a magnetic resonance imaging method that allows for the nondestructive and quantitative determination of glycosaminoglycan concentration in excised cartilage. The technique measures the concentration of the charged contrast agent Gd-DTPA2- (gadolinium diethylenetriamine-pentaacetic acid) equilibrated within cartilage, from which the tissue distribution of glycosaminoglycan can be calculated. The goals of our study were to determine the practicality of nondestructively monitoring glycosaminoglycan concentration in cartilage explants over a long-term culture period and to determine if glycosaminoglycan could be restored to glycosaminoglycan-depleted cartilage explants maintained in long-term culture. To meet our objectives, we harvested bovine cartilage explants, treated them initially with trypsin to reduce the glycosaminoglycan concentration, and cultured them for as long as 8 weeks. Images depicting glycosaminoglycan concentration were calculated from magnetic resonance images acquired at selected intervals during the trypsinization process and the subsequent culture period. The results indicate that gadolinium-enhanced magnetic resonance imaging can follow the reduction of glycosaminoglycan concentration over the course of enzymatic digestion and the replenishment of glycosaminoglycan over several weeks of culture and that cultured cartilage explants are capable of restoring glycosaminoglycan to 85% of its initial concentration. Of particular interest, samples cultured for 5 weeks indicated a depth dependence of glycosaminoglycan regeneration to values similar to the initial physiologic distribution. Thus, this magnetic resonance imaging method may be a very powerful means for exploring the spatial and temporal evolution of glycosaminoglycan in cartilage.     

前列腺癌多参数磁共振成像影像组学研究进展

前列腺癌(prostate cancer,PCa)是最常见的男性泌尿系恶性肿瘤,近来我国前列腺癌的发病率呈明显上升的趋势[1]。多参数磁共振成像(multiparametric magnetic resonance imaging,mp-MRI)对前列腺癌病灶的检测和定位具有较高的敏感性[2]。尽管mp-MRI是一种强大的诊断工具,但是对mp-MRI图像序列的解读准确性仍有待提高[3],不同阅片者对良、恶性病变之间的界定存在高变异性,mp-MRI受到假阳性的限制,仅凭信号强度还不能准确预测和表征病理分级。近年来,许多研究将新兴的影像组学技术应用于mp-MRI诊断前列腺癌的研究中。本文就影像组学在前列腺癌mp-MRI中的研究现状及进展进行综述。