In vivo structural analysis of articular cartilage using diffusion tensor magnetic resonance imaging

Purpose

The articular cartilage is a small tissue with a matrix structure of three layers between which the orientation of collagen fiber differs. A diffusion-weighted twice-refocused spin-echo echo-planar imaging (SE-EPI) sequence was optimized for the articular cartilage, and the structure of the three layers of human articular cartilage was imaged in vivo from diffusion tensor images.

Materials and Methods

The subjects imaged were five specimens of swine femur head after removal of the flesh around the knee joint, five specimens of swine articular cartilage with flesh present and the knee cartilage of five adult male volunteers. Based on diffusion-weighted images in six directions, the mean diffusivity (MD) and the fractional anisotropy (FA) values were calculated.

Results

Diffusion tensor images of the articular cartilage were obtained by sequence optimization. The MD and FA value of the specimens (each of five examples) under different conditions were estimated. Although the articular cartilage is a small tissue, the matrix structure of each layer in the articular cartilage was obtained by SE-EPI sequence with GRAPPA. The MD and FA values of swine articular cartilage are different between the synovial fluid and saline. In human articular cartilage, the load of the body weight on the knee had an effect on the FA value of the surface layer of the articular cartilage.

Conclusion

This method can be used to create images of the articular cartilage structure, not only in vitro but also in vivo. Therefore, it is suggested that this method should support the elucidation of the in vivo structure and function of the knee joint and might be applied to clinical practice.     

Bilaminar pattern of tibial condyle cartilage layer on the fat-suppressed 3D gradient echo images: artifact or structural and biochemical difference in composition of cartilage?

The purpose of this study was to examine if an unusual bilaminar pattern of lateral tibial condyle cartilage layer on the fat-suppressed three-dimensional (3D) spoiled gradient echo sequence is artifactual or correlates with structural and/or biochemical composition of cartilage. The laminar appearance of the lateral tibial condyle cartilage layer was studied on fat-suppressed 3D spoiled gradient echo MR images of the knee joint in 67 patients (mean age: 28y) performed at 1.0 Tesla. After i.v. administration of gadopentetate dimeglumine, diffusion of the contrast media into cartilage layer was qualitatively analysed over time on inversion recovery spin echo images of knee joints of five asymptomatic volunteers (mean age: 25y). In a patient with osteosarcoma and total knee replacement, MR examination of cartilage layer of lateral tibial plateau was compared with histologic specimens stained with Safranin-O, demonstrating proteoglycan distribution in cartilage. The retrospective analysis of 67 knee joints revealed a bilaminar appearance of lateral tibial condyle cartilage layer in the gradient echo images in the majority of cases (81%) with a statistically significant tendency to a trilaminar pattern in patients older than 20 years. With i.v. contrast administration, the contrast enhancement was only observed in the superficial zone of tibial cartilage layer. Histologic specimens in one patient demonstrated a good correlation between thickness of proteoglycan-free and proteoglycan-rich laminae of lateral tibial condyle on Safranin-O staining with hyperintense and hypointense zones, respectively, on corresponding fat-suppressed 3D spoiled gradient echo images (correlation coefficient of 0.87). Bilaminar pattern of tibial condyle cartilage layer on fat-suppressed 3D spoiled gradient echo images in younger subjects is not an artifact or an intrachondral lesion, but it may represent a regional difference in composition of extracellular cartilage matrix possibly produced by a highly-oriented collagen fiber structure associated with a high concentration of proteoglycans in the middle and deep portion of the cartilage layer.     

In vivo triple quantum filtered twisted projection sodium MRI of human articular cartilage

In this work, we present the first triple quantum filtered (TQF) sodium MR images of the human knee joint in vivo. A 3D TQF data set of 16 slices was obtained in 20 min using a TQF pulse sequence preencoded to a twisted projection imaging readout. Images clearly demarcate patellar cartilage and also demonstrate fluid signal suppressed by the triple quantum filter. Biexponential transverse relaxation times were calculated by fitting the TQF free induction decay to a theoretical signal expression. The average values from three healthy volunteers were T(2fall)(*) = 9.59 +/- 0.35 ms and T(2rise)(*) = 0.84 +/- 0.06 ms. Application of TQF imaging in biological tissues is discussed.     

关节软骨光透明的拉曼光谱研究

为探讨原位条件下关节软骨及下骨组织成分含量变化等深层次微观信息,采用拉曼光谱技术结合组织光透明技术来研究软骨组织的光透明效果。选用甘油、碘海醇作为光透明剂,对在不同光透明剂浓度和浸渍时间下的犬膝关节股骨端软骨样本进行拉曼光谱采集。通过计算磷酸基团(920~960 cm-1 ) 和酰胺Ⅰ带(1 595~1 700 cm-1)的积分强度,获得拉曼强度比(磷酸基团/酰胺Ⅰ),探索在不同浸渍时间(10~60 min)、不同浓度下(甘油40%,60%,80%和100%,碘海醇50,150,250和350 mg·mL-1)组织光透明的规律,即寻找合适的透明浓度和透明时间。结果显示：相比于无透明剂情形,两种透明剂均使该强度比信号增强。在同一时间范围内,甘油和碘海醇分别在60%和150 mg·mL-1 浓度下能获得较好的透明效果;而在不同浓度下,甘油的透明效果均在20 min最强,而碘海醇的透明效果一般是在50 min后开始增强。在光透明剂的作用下激发光透过软骨可以直接探测到软骨下骨的拉曼光谱信息,这为研究骨关节炎深层次病因提供了方法和思路。     

风湿性关节炎动物模型中血啉甲醚荧光强度的同步检测研究

光动力疗法的疗效依赖于治疗过程中靶组织中光敏剂的含量或浓度 ,而药物在组织中的分布特性是受动物机体调控的 ,因此 ,同一个体不同组织对光敏剂吸收的时间特性需要同时进行检测才能排除个体之间的差异。建立了一套空间三通道激光诱导荧光同步检测装置 ,并用该装置研究了活体大耳白兔风湿性关节炎模型滑膜、软骨和皮肤对血啉甲醚吸收的时间特性。研究结果表明 ,炎性滑膜组织对血啉甲醚的吸收量远大于软骨和皮肤 ,这一差别在静脉给药即刻就很明显 ,在静脉给药后 2 0min内 ,滑膜中的光敏剂药物含量约为软骨和皮肤中的 6倍。因此 ,对于借助血啉甲醚 ,用光动力疗法治疗风湿性关节炎并采用体外照射治疗方案时 ,从注药即刻开始 ,前 2 0min左右进行光照治疗可能是较好的选择。     

Inter-rater and intra-rater reliability of subchondral bone and cartilage thickness measurement from MRI

MRI is often used to visualize and quantify the articular cartilage layer of load bearing joints affected by degenerative diseases, such as osteoarthritis (OA). Although the role played by the subchondral bone in the etiology and/or progression of OA may be important, the ability to visualize and quantify subchondral bone with MRI has received little attention. In this report we examined the inter-rater and intra-rater reliability of subchondral bone and cartilage thickness measurements from MR images of cadaver femoral head specimens. A 3D-SPGR pulse sequence tuned to eliminate chemical shift artifact through phase cancellation was used to image the specimens. Three raters manually segmented four specimens on two different occasions. Subchondral bone and cartilage thickness measurements were calculated from the segmented images. Inter-rater and intra-rater reliabilities were very high (>.98) for both cartilage and subchondral bone thickness measurements. We conclude that subchondral bone thickness can be measured as reliably as cartilage thickness from MR images.     

Optimization and validation of a rapid high-resolution T1-w 3D FLASH water excitation MRI sequence for the quantitative assessment of articular cartilage volume and thickness

In view of follow up, survey and development of therapeutic strategies for osteoarthritis where cartilage deterioration plays an important role, a non invasive, reliable and quantitative assessment of the articular cartilage is desirable. The currently available high resolution T(1)-weighted (T1-w) 3D FLASH pulse sequences with frequency selective fat suppression are very time consuming. We have 1) optimized a high resolution T1-w 3D FLASH water excitation (WE) sequence for short acquisition time and cartilage visualization, and 2) validated this sequence for cartilage volume and thickness quantification. The spectral fat presaturation was replaced by selective water excitation. The flip angle of the WE sequence was optimized for the contrast to noise (C/N(cart)) ratio of cartilage. Sagittal datasets (voxel size: 0.31 x 0.31 x 2 mm(3)) of the knees of nine healthy volunteers were acquired both, with the 3D FLASH WE (17.2/6.6/30 degrees ) sequence (WE) and a previously validated 3D FLASH fat saturated (42/11/30 degrees ) sequence (FS). For validation of the WE sequence, cartilage volume, mean and maximal cartilage thickness of the two sequences were compared. Reproducibility was assessed by calculating the coefficient of variation (COV %) of 4 consecutive WE data sets in the volunteers. The acquisition time was reduced from 16'30" (FS) down to 7'14" for the WE sequence. Image contrast and visualization of the cartilage was very similar, but delineation of the basal layer of the cartilage was slightly improved with the WE sequence. A flip angle of 30 degrees provided the best C/N(cart) ratios (WE). Reproducibility (COV) was between 1.9 and 5.9%. Cartilage volume and thickness agreed within 4% between FS and WE sequence. The WE sequence allows for rapid, valid and reproducible quantification of articular cartilage volume and thickness, prerequisites for follow-up examinations. The reduced acquisition time (50% of FS) enables routine clinical application and thus may contribute to a broader assessment of osteoarthritis.     

Qualitative and quantitative ultrashort echo time (UTE) imaging of cortical bone

We describe the use of two-dimensional ultrashort echo time (2D UTE) sequences with minimum TEs of 8 μs to image and quantify cortical bone on a clinical 3T scanner. An adiabatic inversion pulse was used for long T(2) water and fat signal suppression. Adiabatic inversion prepared UTE acquisitions with varying TEs were used for T(2) measurement. Saturation recovery UTE acquisitions were used for T(1) measurement. Bone water concentration was measured with the aid of an external reference phantom. UTE techniques were evaluated on cadaveric specimens and healthy volunteers. A signal-to-noise ratio of around 30, contrast-to-noise ratio of around 27/20 between bone and muscle/fat were achieved in tibia in vivo with a nominal voxel size of 0.23 × 0.23 × 6.0 mm(3) in a scan time of 5 min. A mean T(1) of 223 ± 11 ms and mean T(2) of 390 ± 19 μs were found. Mean bone water concentrations of 23.3 ± 1.6% with UTE and 21.7 ± 1.3% with adiabatic inversion prepared UTE sequences were found in tibia in five normal volunteers. The results show that in vivo qualitative and quantitative evaluation of cortical bone is feasible with 2D UTE sequences.     

Thermoacoustic assessment of hematocrit changes in human forearms

Abnormal hematocrit(Hct) is associated with an increased risk of pre-hypertension and all-cause death in general population, and people with a high Hct value are susceptible to arterial cardiovascular disease and venous thromboembolism.In this study, we report for the first time on the ability of thermoacoustic imaging(TAI) for in vivo evaluating Hct changes in human forearms. In vitro blood samples with different Hct values from healthy volunteers(n = 3) were prepared after centrifugation. TAI was performed using these samples in comparison with the direct measurements of conductivity. In vivo TAI was conducted in the forearm of healthy volunteers(n = 7) where Hct changes were produced through a vascular occlusion stimulation over a period of time. The results of in vitro blood samples obtained from the 3 healthy subjects show that the thermoacoustic(TA) signals changes due to the variation of blood conductivity are closely related to the changes in Hct. In addition, the in vivo TA signals obtained from the 7 healthy subjects consistently increase in the artery/muscle and decrease in the vein during venous or arterial occlusion because of the changed Hct value in their forearms. These findings suggest that TAI has the potential to become a new tool for monitoring Hct changes for a variety of pre-clinical and clinical applications.     

Ultrasound elastomicroscopy using water jet and osmosis loading: potentials for assessment for articular cartilage

Research in elasticity imaging typically relies on 1-10 MHz ultrasound. Elasticity imaging at these frequencies can provide strain maps with a resolution in the order of millimeters, but this is not sufficient for applications to skin, articular cartilage, or other fine structures. In this paper, we introduced two methods of ultrasound elastomicroscopy using water jet and osmosis loading for imaging the elasticity of biological soft tissues with high resolutions. In the first system, the specimens were compressed using water jet compression. A water jet was used to couple a focused 20 MHz ultrasound beam into the specimen and meanwhile served as a "soft" indenter. Because there was no additional attenuation when propagating from the ultrasound transducer to the specimen, the ultrasound signal with high signal-to-noise ratio could be collected from the specimens simultaneously with compressing process. The compression was achieved by adjusting the water flow. The pressure measured inside the water pipe and that on the specimen surface was calibrated. This system was easily to apply C-scan over sample surfaces. Experiments on the phantoms showed that this water jet indentation method was reliable to map the tissue stiffness distribution. Results of 1D and 2D scanning on phantoms with different stiffness are reported. In the second system, we used osmotic pressure caused by the ion concentration change in the bathing solutions for the articular cartilage to deform them. When bovine articular cartilage specimens were immerged in solutions with different salt concentration, a 50 MHz focused ultrasound beam was used to monitor the dynamic swelling or shrinkage process. Results showed that the system could reliably map the strain distribution induced by the osmotic loading. We extract intrinsic layered material parameters of the articular cartilage using a triphasic model. In addition to biological tissues, these systems have potential applications for the assessment of bioengineered tissues, biomaterials with fine structures, or some engineering materials. Further studies are necessary to fully realize the potentials of these two new methods.     

Articular cartilage evaluation in osteoarthritis of the hip with MR imaging under continuous leg traction

We conducted MR evaluations of acetabular and femoral cartilages in 27 hips of patients with osteoarthritis and 10 hips of normal volunteers by a fat-suppressed three-dimensional (3D) pulse sequence using a continuous leg traction method, and correlated the results with radiographic assessment. Normal condition of the acetabular and femoral cartilages was clearly demonstrated in the normal volunteers. Grading of abnormalities was possible for each cartilage in the patients with osteoarthritis. In early osteoarthritis graded by radiography, a high prevalence of abnormalities was detected in the acetabular cartilage as compared with the femoral cartilage. Despite the structural difficulty in evaluation of the hip joint cartilage, our MR imaging technique can provide information concerning a wide spectrum of cartilage abnormalities even in the identical radiographic stage, which will lead to improvement in the evaluation of disease progression and in surgical planning.     

Evaluation of water content by spatially resolved transverse relaxation times of human articular cartilage

Non-invasive assessment of cartilage properties, specifically water content, could prove helpful in the diagnosis of early degenerative joint diseases. Transverse relaxation times T(2) of human articular cartilage (34 cartilage slices of three donors) were measured on a pixel-by-pixel basis in a clinical whole body MR system in vitro. In vivo feasibility to measure quantitative T(2) maps was shown for human patellar cartilage. The relaxation times of cartilage with collagen in the radial zone oriented perpendicular to the magnetic field increased from approximately 10 ms near the bone to approximately 60 ms near the articular surface. Cartilage water content of the tibial plateau and femoral condyles could be determined from the correlation with T(2) (R(2) = 0.71) with an error of approximately 2 wt.%. In vivo, directional variation would need to be considered. If confirmed in vivo, T(2) measurements could potentially serve as a non-invasive tool for the evaluation of the status and distribution of water content in articular cartilage.     

In vivo 31P echo-planar spectroscopic imaging of human calf muscle

Localized phosphorus-31 NMR spectra of human calf muscle in vivo were obtained by means of echo-planar spectroscopic imaging (EPSI) with a 1.5-T whole-body scanner. The technique permits the measurement of two-dimensional 31P SI data at a minimum acquisition time of 2.4 s (8x8 voxels, TR=300 ms). With 9.4 min measurement time (TR=1100 ms, 64 averages) and 25x25x40 mm spatial resolution in vivo the 31P NMR signal-to-noise ratio (S/N) of the phosphocreatine (PCr) resonance was about 45; the multiplets of nucleoside 5'-triphosphates were resolved. Spectral quality permits quantitative assessment of the PCr signal in a measurement time that is shorter by a factor of 2 or more than the minimum measurement time feasible with chemical-shift imaging. In a functional EPSI study with a time resolution of 20.5 s on the calf muscle of volunteers, spectra showed a 40% decrease of the PCr signal intensity (at rest: S/N congruent with12) upon exertion of the muscle.     

Degenerative cartilage lesions of the hip--magnetic resonance evaluation

The capability of magnetic resonance imaging (MRI) to visualize early degenerative arthritis of the hip was investigated. The study was performed on 8 healthy students and 45 elderly volunteers. Images were obtained by using an electronically variable Helmholtz coil (switched-array coil, SAC). In order to diagnose degenerative lesions of the joint cartilage, FISP sequences with a flip angle of 70 degrees were found preferable to compared sequences. MRI-detectable signs of degenerative arthritis of the hip were narrowed joint space due to partially thinned cartilage layers, focal areas of either increased or decreased signal intensity in the hyaline cartilage, complete loss of cartilage, and signal variation in the bone marrow. MRI of the hip may be appropriate to detect early degenerative changes in the hips of young high-risk patients to facilitate therapy planning.     

MR protocols for imaging the guinea pig knee

Magnetic resonance images of the femorotibial joints of male Dunkin-Hartley guinea pigs were obtained in two and three dimensions at 2.35 T using a wide range of T₁- and T₂-weighted imaging sequences. The effect of slice position on visualisation of articular cartilage, bone and periarticular tissues in sagittal and coronal sections was investigated along with the resolution and signal/noise ratio achievable. Based on that survey, a two-dimensional spin echo sequence (repetition time = 1500 ms, echo time = 40 ms) was found to give optimum visualisation of the normal joint anatomy with in-plane resolution of 75 × 150 μm and a 1 mm slice thickness in an imaging time of 25 min. This protocol was also found to be highly effective in distinguishing many features of the spontaneous, osteoarthritic-like pathology found in the joints of older animals compared to juveniles and therefore provides a means of monitoring disease progression longitudinally. Three-dimensional spin echo imaging methods demonstrated focal changes in signal intensity in the articular cartilage of the medial tibial plateau in older animals. The resulting imaging times of several hours, however, precludes their routine use in vivo.     

Compartmental approach for evaluation of plasma kinetics and (13)co(2)-exhalation after oral loading with L-[1-(13)c]leucine

Abstract A seven compartment model was applied for evaluation of oral L-[1-(13)C]leucine loading tests (38 μmol/kg body wt.) in healthy volunteers. The model comprises transport and absorption in stomach and gut into a central L-leucine-compartment which is connected to a protein compartment and to the compartment of the corresponding 2-oxo acid. CO(2) release from the latter occurs in a fast and a slow compartment into the central CO(2) compartment for exhalation. Using the fmins routine of MATLAB for parameter estimation, a good agreement was obtained between calculated and actually measured kinetics of (13)C-labelled metabolites and a mean in vivo L-leucine oxidation of 0.365 ± 0.071 μmol/kg per min (n = 5) was computed. Plausibility of the model was checked by predicting in vivo leucine oxidation rates from primed continuous infusion tests (priming: L-[1-(13)C]leucine, 5 μmol/kg; NaH(13)CO(2), 1.2 μmol/kg; infusion: L-[1-(13)C]leucine, 5 μmol/kg per h). In 5 tested volunteers, the experimental L-leucine oxidation rate amounted to 0.358 ± 0.105 μmol/kg per min versus predicted 0.324±0.099 μmol/kg per min. Possible causes for some observed intraindividual variations are discussed.     

In vivo Raman spectroscopic analysis of the influence of UV radiation on carotenoid antioxidant substance degradation of the human skin

It is well known from the literature that carotenoid antioxidant substances decrease after the irradiation of the skin with UV light. Available literature has shown no information about the response time and total dynamics of degradation of carotenoid antioxidants after UV irradiation. The measurements were made with the HPLC method, which is time-consuming and does not give relevant information about the dynamics of degradation of carotenoids in the skin after UV irradiation. With the introduction of new noninvasive spectroscopic methods, it became possible to measure in vivo the behavior of carotenoid antioxidant substances, such as betacarotene and lycopene in the skin after UV light exposure. In the present study, the resonance Raman spectroscopy method was used as a fast and noninvasive optical method to measure the dynamics of degradation of beta-carotene and lycopene in living human skin after UV exposure. It was found that the beta-carotene and lycopene concentration in the skin does not decrease immediately after UV irradiation. There is a time delay, which varies from 30 up to 90 min for beta-carotene and from 0 up to 30 min for lycopene. A strong nonlinear correlation between the individual antioxidant level of volunteers and the magnitude of destruction of antioxidants in the skin was found.     

A feasibility study of in vivo T1rho imaging of the intervertebral disc

PURPOSE: Recent studies have proposed that magnetic resonance (MR) T1rho relaxation time is associated with loss of macromolecules. The depletion of macromolecules in the matrix of the intervertebral disc may be an initiating factor in degenerative disc disease. The purpose of this study was to test the feasibility of quantifying T1rho relaxation time in phantoms and intervertebral discs of healthy volunteers using in vivo MR imaging at 3 T. MATERIALS AND METHODS: A multislice T1rho spiral sequence was used to quantify T1rho relaxation time in phantoms with different agarose concentrations and in the intervertebral discs of 11 healthy volunteers (mean age=31.3 years; age range=23-60 years; gender: 5 females, 6 males). RESULTS: The phantom studies demonstrated the feasibility of using spiral imaging at 3 T. The in vivo results indicate that the median T1rho value of the nucleus (116.6+/-21.4 ms) is significantly greater (P<0.05) than that of the annulus (84.1+/-11.7 ms). The correlations between the age of the volunteers and T1rho relaxation time in the nucleus (r2=-0.82; P=0.0001) and the annulus (r2=-0.37; P=0.04) were significant. A trend of decreasing T1rho values from L3-4 to L4-5 to L5-S1 was evident. CONCLUSION: The results of this study suggest that in vivo T1rho quantification is feasible and may potentially be a clinical tool in identifying early degenerative changes in the intervertebral disc.     

Investigation of laminar appearance of articular cartilage by means of magnetic resonance microscopy

Magnetic resonance (MR) images and relaxation and diffusion maps of articular cartilage were obtained to explain discrepancies in its MR appearance. Porcine specimens were studied only by MR microscopy. For human specimens a combination of MR microscopy and large-scale MR imaging was used. Common features in the laminar structures of human and porcine samples are described. It was found that the decay of transverse magnetization was nonexponential with a rapidly decaying component which prevented construction of reliable proton-density maps. Dependence of T₂ values on the orientation of specimens in the magnetic field as well as magnetization transfer experiments supported the previous suggestions about a significant role of dipolar interaction with protons of collagen in the laminar appearance of articular cartilage. The loss of the laminar structure induced by rotation of the human cartilage specimen around the axis normal to its surface demonstrated nonuniform angular distribution of the collagen fibers within the layer.     

Sodium visibility and quantitation in intact bovine articular cartilage using high field (23)Na MRI and MRS

Noninvasive methods of detecting cartilage degeneration can have an impact on identifying the early stages of osteoarthritis. Accurate measurement of sodium concentrations within the cartilage matrix provides a means for analyzing tissue integrity. Here a method is described for quantitating sodium concentration and visibility in cartilage, with general applications to all tissue types. The sodium concentration in bovine patellar cartilage plugs was determined by three different methods: NMR spectroscopy of whole cartilage plugs, NMR spectroscopy of liquefied cartilage in concentrated HCl, and inductively coupled plasma emission spectroscopy. Whole bovine patellae were imaged with relaxation normalized calibration phantoms to ascertain sodium concentrations inside the articular cartilage. Sodium concentrations in intact articular cartilage were found to range from approximately 200 mM on the edges to approximately 390 mM in the center, with an average of approximately 320 mM in five separate bovine patellae studied. In essence, we have created sodium distribution maps of the cartilage, showing for the first time, spatial variations of sodium concentration in intact cartilage. This average concentration measurement correlates very well with the values obtained from the spectroscopic methods. Furthermore, sodium was found to be 100% NMR visible in cartilage plugs. Applications of this method in diagnosing and monitoring treatment of osteoarthritis are discussed.