Prediction of cartilage compressive modulus using multiexponential analysis of T2 relaxation data and support vector regression

Evaluation of mechanical characteristics of cartilage by magnetic resonance imaging would provide a noninvasive measure of tissue quality both for tissue engineering and when monitoring clinical response to therapeutic interventions for cartilage degradation. We use results from multiexponential transverse relaxation analysis to predict equilibrium and dynamic stiffness of control and degraded bovine nasal cartilage, a biochemical model for articular cartilage. Sulfated glycosaminoglycan concentration/wet weight (ww) and equilibrium and dynamic stiffness decreased with degradation from 103.6 ± 37.0 µg/mg ww, 1.71 ± 1.10 MPa and 15.3 ± 6.7 MPa in controls to 8.25 ± 2.4 µg/mg ww, 0.015 ± 0.006 MPa and 0.89 ± 0.25MPa, respectively, in severely degraded explants. Magnetic resonance measurements were performed on cartilage explants at 4 °C in a 9.4 T wide‐bore NMR spectrometer using a Carr–Purcell–Meiboom–Gill sequence. Multiexponential T₂ analysis revealed four water compartments with T₂ values of approximately 0.14, 3, 40 and 150 ms, with corresponding weight fractions of approximately 3, 2, 4 and 91%. Correlations between weight fractions and stiffness based on conventional univariate and multiple linear regressions exhibited a maximum r² of 0.65, while those based on support vector regression (SVR) had a maximum r² value of 0.90. These results indicate that (i) compartment weight fractions derived from multiexponential analysis reflect cartilage stiffness and (ii) SVR‐based multivariate regression exhibits greatly improved accuracy in predicting mechanical properties as compared with conventional regression. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Effect of glycogen loading on skeletal muscle cross‐sectional area and T2 relaxation time

This study was performed to investigate if glycogen loading of skeletal muscles, by binding water, would effect the cross‐sectional area (CSA) and if an altered water content would alter the transverse relaxation time (T2) measured by magnetic resonance imaging (MRI). Five healthy volunteers participated in a programme with 4 days of extremely carbohydrate‐restricted meals followed by 4 days of extremely high carbohydrate intake. The CSA and T2 of thigh and calf muscles were related to the intramuscular glycogen content evaluated at days 4 and 8. An increase in glycogen content from 281 to 634 mmol kg^–1 dry wt increased the CSA of the vastus muscles by 3.5% from 78 ± 11 to 80 ± 12 cm² and the thigh circumference by 2.5% from 146 ± 20 to 150 ± 23 cm². Calf circumference increased non‐significantly by 4% from 78 ± 15 to 82 ± 19 cm². Mono‐exponential T2 decreased in m tibialis anterior from 27.8 ± 1.2 to 26.9 ± 1.7 ms, did not change in m. vastus lateralis 26.5 ± 1.9 ms/26.6 ± 1.3 ms or in m. gastrocnemius 29.5 ± 1.0 ms/29.8 ± 1.9 ms. Glycogen loading increased the signal intensity mainly at different echo times (TE) 15 and 30 ms. The study shows that increased glycogen filling in the muscles increases muscle CSA and that this can be detected by MRI. The signal intensity increased the most at shorter TEs suggesting a more tight intracellular binding of water in glycogen loaded muscles.     

Measuring renal tissue relaxation times at 7 T

As developments in RF coils and RF management strategies make performing ultra‐high‐field renal imaging feasible, understanding the relaxation times of the tissue becomes increasingly important for tissue characterization, sequence optimization and quantitative functional renal imaging, such as renal perfusion imaging using arterial spin labeling. By using a magnetization‐prepared single‐breath‐hold fast spin echo imaging method, human renal T₁ and T₂ imaging studies were successfully performed at 7 T with 11 healthy volunteers (eight males, 45 ± 17 years, and three females, 29 ± 7 years, mean ± standard deviation, S.D.) while addressing challenges of B₁⁺ inhomogeneity and short‐term specific absorption rate limits. At 7 T, measured renal T₁ values for the renal cortex and medulla (mean ± S.D.) from five healthy volunteers who participated in both 3 T and two‐session 7 T studies were 1661 ± 68 ms and 2094 ± 67 ms, and T₂ values were 108 ± 7 ms and 126 ± 6 ms. For comparison, similar measurements were made at 3 T, where renal cortex and medulla T₁ values of 1261 ± 86 ms and 1676 ± 94 ms and T₂ values of 121 ± 5 ms and 138 ± 7 ms were obtained. Measurements at 3 T and 7 T were significantly different for both T₁ and T₂ values in both renal tissues. Reproducibility studies at 7 T demonstrated that T₁ and T₂ estimations were robust, with group mean percentage differences of less than 4%. Copyright © 2014 John Wiley & Sons, Ltd.     

T2 measurement of J-coupled metabolites in the human brain at 3T

Proton T₂ relaxation times of metabolites in the human brain were measured using point resolved spectroscopy at 3T in vivo. Four echo times (54, 112, 246 and 374 ms) were selected from numerical and phantom analyses for effective detection of the glutamate multiplet at ~ 2.35 ppm. In vivo data were obtained from medial and left occipital cortices of five healthy volunteers. The cortices contained predominantly gray and white matter, respectively. Spectra were analyzed with LCModel software using volume‐localized calculated spectra of brain metabolites. The estimate of the signal strength vs. TE was fitted to a monoexponential function for estimation of apparent T₂ (T₂^?). T₂^? was estimated to be similar between the brain regions for creatine, choline, glutamate and myo‐inositol, but significantly different for N‐acetylaspartate singlet and multiplet. T₂^?s of glutamate and myo‐inositol were measured as 181 ± 16 and 197 ± 14 ms (mean ± SD, N = 5) for medial occipital cortices, and 180 ± 12 and 196 ± 17 ms for left occipital cortices, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Improved specificity of cartilage matrix evaluation using multiexponential transverse relaxation analysis applied to pathomimetically degraded cartilage

The noninvasive early detection of specific matrix alterations in degenerative cartilage disease would be of substantial use in basic science studies and clinically, but remains an elusive goal. Recently developed MRI methods exhibit some specificity, but require contrast agents or nonstandard pulse sequences and hardware. We present a multiexponential approach which does not require contrast agents or specialized hardware, and uses a standard multiple‐echo spin‐echo sequence. Experiments were performed on tissue models of degenerative cartilage using enzymes with distinct actions. MR results were validated using histologic, biochemical and infrared spectroscopic analyses. The sulfated glycosaminoglycan per dry weight (dw) in bovine nasal cartilage was 0.72 ± 0.06 mg/mg dw and was reduced through chondroitinase AC and collagenase digestion to 0.56 ± 0.12 and 0.58 ± 0.13 mg/mg dw, respectively. Multiexponential analysis of data obtained at 9.4 T permitted the identification of tissue compartments assigned to the proteoglycan component of the matrix and to bulk water. Enzymatic treatment resulted in a significant reduction in the ratio of proteoglycan‐bound to free water from 0.13 ± 0.02 in control cartilage to 0.03 ± 0.02 and 0.05 ± 0.06 under chondroitinase AC and collagenase treatment, respectively. As expected, monoexponential T₂ increased with both degradation protocols, but without further specificity to the nature of the degradation. An important eventual extension of this approach may be to map articular cartilage degeneration in the clinical setting. As an initial step towards this, localized multiexponential T₂ analysis was performed on control and trypsin treated excised bovine patella. The results obtained on this articular cartilage sample were readily interpretable in terms of proteoglycan‐associated and relatively free water compartments. In potential clinical applications, signal‐to‐noise ratio constraints will define the threshold for the detection of macromolecular compartment changes at a given spatial scale. The multiexponential approach has potential application to the early detection of cartilage degradation with the use of appropriate pulse parameters under high signal‐to‐noise ratio conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

基于定量动态负荷下膝关节骨性关节炎软骨MRIT2时间表现研究

目的通过比较膝关节骨性关节炎（OA）病人定量动态负荷前后膝关节软骨T2时间变化情况,分析MRIT2mapping序列反映软骨基质生物力学变化的灵敏度．并验证高磁场条件下人体关节负荷装置的有效性。方法10例膝关节OA病人,其中男性3例．女性7例：年龄4l～66岁．平均年龄57-3岁。依托人体下肢关节力学负荷装置,对其施加膝关节动态负荷。负荷前后行膝关节MRIT2maDping成像,将膝关节轴向负荷区软骨分为4个部位：胫骨平台内、外侧软骨区及股骨内、外侧髁软骨区．分别测量各部位软骨负荷前后的T,时间。对负荷前膝关节内、外侧软骨分级评估进行卡方检验,对同一软骨区动态负荷前后的T2时间进行配对t检验。结果负荷前膝关节内外侧软骨分级差异无统计学意义（P〉0．05）。OA病人负荷前后T2值,胫骨平台内侧软骨区分别为（39．59±4．17）ms、（40．14±4．49）ms（f=0．426,P=0．680）;胫骨平台外侧软骨区（38．85±6．72）ms、（41．25±6．54）ms（t=1．704,P=0．123）：股骨内侧髁软骨区（36．44±5．72）ms、（40．63±4．90）ms（t=1．783,P=0．108）;股骨外侧髁软骨区（39．30±5．78）ms、（46．14±5．03）ms（t=2．826,P=0．020）。结论OA病人负荷后膝关节局部区域软骨区T2时间延长．自行设计的动态加压装置适合在高磁场条件下完成加压及MRI检查,有一定推广意义。     

Associations between the properties of the cartilage matrix and findings from quantitative MRI in human osteoarthritic cartilage of the knee

The aim of this study was to investigate the associations between the properties of the cartilage matrix and the results of T2 mapping and delayed gadolinium-enhanced magnetic resonance imaging (dGEMRIC) in human knee osteoarthritic cartilage. Osteochondral samples were harvested from the middle part of the femoral condyle and tibial plateaus of 20 patients with knee osteoarthritis (OA) during total knee arthroplasty. Sagittal T2 mapping, T1pre, and T1Gd were performed using 7.0T magnetic resonance imaging (MRI). Gycosaminoglycan (GAG) distribution was evaluated by OARSI, collagen anisotropy was assessed by polarized light microscopy (PLM), and biochemical analyses measured water, GAG, and collagen content. Associations between properties of the cartilage matrix and T2 and ΔR1 (1/T1Gd-1/T1pre) values were explored using correlation analysis. T2 and ΔR1 values were significantly correlated with the degree of cartilage degeneration (OARSI grade; Ρ = 0.53 and 0.77). T2 values were significantly correlated with water content (r = 0.69; P < 0.001), GAG content (r = -0.43; P < 0.001), and PLM grade (r = 0.47; P < 0.001), but not with collagen content (r = -0.02; P = 0.110). ΔR1 values were significantly correlated with GAG content (r = -0.84; P < 0.001) and PLM grade (r = 0.41; P < 0.001). Taken together, T2 mapping and dGEMRIC results were correlated with the properties of the cartilage matrix in human knee osteoarthritic cartilage. Combination T2 mapping and dGEMRIC represents a potential non-invasive monitoring technique to detect the progress of knee OA.     

Quantitative T1 mapping indicates tumor infiltration beyond the enhancing part of glioblastomas

The aim of this study was to evaluate whether maps of quantitative T1 (qT1) differences induced by a gadolinium‐based contrast agent (CA) are better suited than conventional T1‐weighted (T1w) MR images for detecting infiltration inside and beyond the peritumoral edema of glioblastomas. Conventional T1w images and qT1 maps were obtained before and after gadolinium‐based CA administration in 33 patients with glioblastoma before therapy. The following data were calculated: (i) absolute qT1‐difference maps (qT1 pre‐CA ‐ qT1 post‐CA), (ii) relative qT1‐difference maps, (iii) absolute and (iv) relative differences of conventional T1w images acquired pre‐ and post‐CA. The values of these four datasets were compared in four different regions: (a) the enhancing tumor, (b) the peritumoral edema, (c) a 5 mm zone around the pathology (defined as the sum of regions a and b), and (d) the contralateral normal appearing brain tissue. Additionally, absolute qT1‐difference maps (displayed with linear gray scaling) were visually compared with respective conventional difference images. The enhancing tumor was visible both in the difference of conventional pre‐ and post‐CA T1w images and in the absolute qT1‐difference maps, whereas only the latter showed elevated values in the peritumoral edema and in some cases even beyond. Mean absolute qT1‐difference values were significantly higher (P < 0.01) in the enhancing tumor (838 ± 210 ms), the peritumoral edema (123 ± 74 ms) and in the 5 mm zone around the pathology (81 ± 31 ms) than in normal appearing tissue (32 ± 35 ms). In summary, absolute qT1‐difference maps—in contrast to the difference of T1w images—of untreated glioblastomas appear to be able to visualize CA leakage, and thus might indicate tumor cell infiltration in the edema region and beyond. Therefore, the absolute qT1‐difference maps are potentially useful for treatment planning.     

Magic angle effect on adiabatic T1ρ imaging of the Achilles tendon using 3D ultrashort echo time cones trajectory

The protons in collagen‐rich musculoskeletal (MSK) tissues such as the Achilles tendon are subject to strong dipolar interactions which are modulated by the term (3cos²θ‐1) where θ is the angle between the fiber orientation and the static magnetic field B₀. The purpose of this study was to investigate the magic angle effect in three‐dimensional ultrashort echo time Cones Adiabatic T_1ρ (3D UTE Cones‐AdiabT_1ρ) imaging of the Achilles tendon using a clinical 3 T scanner. The magic angle effect was investigated by Cones‐AdiabT_1ρ imaging of five cadaveric human Achilles tendon samples at five angular orientations ranging from 0° to 90° relative to the B₀ field. Conventional Cones continuous wave T_1ρ (Cones‐CW‐T_1ρ) and Cones T₂* (Cones‐T₂*) sequences were also applied for comparison. On average, Cones‐AdiabT_1ρ increased 3.6‐fold from 13.6 ± 1.5 ms at 0° to 48.4 ± 5.4 ms at 55°, Cones‐CW‐T_1ρ increased 6.1‐fold from 7.0 ± 1.1 ms at 0° to 42.6 ± 5.2 ms at 55°, and Cones‐T2* increased 12.3‐fold from 2.9 ± 0.5 ms at 0° to 35.8 ± 6.4 ms at 55°. Although Cones‐AdiabT_1ρ is still subject to significant angular dependence, it shows a much‐reduced magic angle effect compared to Cones‐CW‐T_1ρ and Cones‐T₂*, and may be used as a novel and potentially more effective approach for quantitative evaluation of the Achilles tendon and other MSK tissues.     

Shortening of apparent transverse relaxation time of inorganic phosphate as a breast cancer biomarker

Phosphorus MRS offers a non‐invasive tool for monitoring cell energy and phospholipid metabolism and can be of additional value in diagnosing cancer and monitoring cancer therapy. In this study, we determined the transverse relaxation times of a number of phosphorous metabolites in a group of breast cancer patients by adiabatic multi‐echo spectroscopic imaging at 7 T. The transverse relaxation times of phosphoethanolamine, phosphocholine, inorganic phosphate (P_i), glycerophosphocholine and glycerophosphatidylcholine were 184 ± 8 ms, 203 ± 17 ms, 87 ± 8 ms, 240 ± 56 ms and 20 ± 10 ms, respectively. The transverse relaxation time of P_i in breast cancer tissue was less than half that of healthy fibroglandular tissue. This effect is most likely caused by an up‐regulation of glycolysis in breast cancer tissue that leads to interaction of P_i with the GAPDH enzyme, which forms part of the reversible pathway of exchange of P_i with gamma‐adenosine tri‐phosphate, thus shortening its apparent transverse relaxation time. As healthy breast tissue shows very little glycolytic activity, the apparent T₂ shortening of P_i due to malignant transformation could possibly be used as a biomarker for cancer.     

Adiabatic multi‐echo 31P spectroscopic imaging (AMESING) at 7 T for the measurement of transverse relaxation times and regaining of sensitivity in tissues with short T2* values

An adiabatic multi‐echo spectroscopic imaging (AMESING) sequence, used for ³¹P MRSI, with spherical k‐space sampling and compensated phase‐encoding gradients, was implemented on a whole‐body 7‐T MR system. One free induction decay (FID) and up to five symmetric echoes can be acquired with this sequence. In tissues with low T₂* and high T₂, this can theoretically lead to a potential maximum signal‐to‐noise ratio (SNR) increase of almost a factor of three, compared with a conventional FID acquisition with Ernst‐angle excitation. However, with T₂ values being, in practice, ≤400 ms, a maximum enhancement of approximately two compared with low flip Ernst‐angle excitation should be feasible. The multi‐echo sequence enables the determination of localized T₂ values, and was validated with ³¹P three‐dimensional MRSI on the calf muscle and breast of a healthy volunteer, and subsequently applied in a patient with breast cancer. The T₂ values of phosphocreatine, phosphodiesters (PDE) and inorganic phosphate in calf muscle were 193 ± 5 ms, 375 ± 44 ms and 96 ± 10 ms, respectively, and the apparent T₂ value of γ‐ATP was 25 ± 6 ms. A T₂ value of 136 ± 15 ms for inorganic phosphate was measured in glandular breast tissue of a healthy volunteer. The T₂ values of phosphomonoesters (PME) and PDE in breast cancer tissue (ductulolobular carcinoma) ranged between 170 and 210 ms, and the PME to PDE ratios were calculated to be phosphoethanolamine/glycerophosphoethanolamine = 2.7, phosphocholine/glycerophosphocholine = 1.8 and PME/PDE = 2.3. Considering the relatively short T₂* values of the metabolites in breast tissue at 7 T, the echo spacing can be short without compromising spectral resolution, whilst maximizing the sensitivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Tissue response to porous high density polyethylene as a three-dimensional scaffold for bone tissue engineering: An experimental study

High density polyethylene (HDPE) is a synthetic biomaterial used as a three-dimensional scaffold for bone defect reconstruction. Reports differ with regard to its biological response, particularly its osteoconductive capacity. The aim of the present work was to histologically and histomorphometrically evaluate tissue response to porous HDPE. An in vivo study was conducted in rat tibia to evaluate osteogenic capacity, angiogenesis, inflammatory response, and the presence of multinucleated giant cells 14 and 60?days post-biomaterial implantation. Histological examination 14?days post-implantation showed fibrovascular tissue inside pores and on the surface of porous HDPE, acute inflammatory response, scant multinucleated giant cells (MNGCs), and lamellar bone in contact with the biomaterial. An increase in the proportion of lamellar bone tissue, no inflammatory response, and a decrease in the number of MNGCs were observed at 60?days. The histomorphometric study showed a significant time-dependent increase both in the area of bone tissue formed in contact with the porous HDPE (14d: 24.450?±?11.623 µm² vs. 60d: 77.104?±?26.217 µm², p?<?0.05) and in the percentage of bone tissue in contact with the porous HDPE (osseointegration). A significant decrease in the number of MNGCs was also observed at 60?days post-implantation. Porous HDPE showed adequate osteoconductive properties, and only caused an initial inflammatory response. Although this biomaterial has traditionally been used juxtaosseoulsy, its adequate osteoconductive properties broaden the scope of its application to include intraosseous placement.     

Effect of translation and rotation fitting on analysis of corneal topography

Abstract

The purpose was to assess the suitability of quadratic equations for the accurate representation of corneal topography and consider the effect of translation and rotation fitting on the quality of fit and the curvature results. Topography images were recorded for the anterior and posterior surfaces of 490 corneas of 490 myopic patients using Pentacam. Elevation data were fitted to four shape models, three of which considered translational and/or rotational fitting. Differences between the models in the estimates of radii of curvature (R) and asphericity coefficients (Q) and in the quality of fit (as measured by the root mean square (RMS) error and the structural similarity index (SSIM)) were statistically analysed. The general shape model that considered both translational and rotational misalignments provided the best fit for the anterior (RMS?=?1.18?±?0.56?µm, SSIM?=?0.99?±?0.01) and posterior (RMS 3.64?±?1.23?µm, SSIM?=?0.99?±?0.01) corneal surfaces in all subjects. The quality of fit degraded significantly (with p?<?0.01 in all cases) when misalignments were not considered, increasing RMS to 5.20?±?2.27?µm (anterior) and 17.10?±?6.08?µm (posterior) and decreasing SSIM to 0.84?±?0.18 (anterior) and 0.68?±?0.22 (posterior) when both translational and rotational misalignments were ignored. The estimates of R_x, R_y, Q_x and Q_y as obtained when both forms of misalignment were considered varied, respectively, by as much as 0.18?mm, 0.23?mm, 0.27 and 0.54 for the anterior surface, and 0.25?mm, 0.39?mm, 0.32 and 0.37 for the posterior surface when misalignments were ignored. The variations were statistically significant, with p remaining below 0.01 in all cases. In conclusion, consideration of geometric misalignments helps improve the accuracy of describing corneal topography. The effects of misalignments on the estimates of corneal radius and asphericity are statistically significant and may in some cases be clinically significant.     

Proton and phosphorus magnetic resonance spectroscopy of the healthy human breast at 7 T

In vivo water‐ and fat‐suppressed ¹H magnetic resonance spectroscopy (MRS) and ³¹P magnetic resonance adiabatic multi‐echo spectroscopic imaging were performed at 7 T in duplicate in healthy fibroglandular breast tissue of a group of eight volunteers. The transverse relaxation times of ³¹P metabolites were determined, and the reproducibility of ¹H and ³¹P MRS was investigated. The transverse relaxation times for phosphoethanolamine (PE) and phosphocholine (PC) were fitted bi‐exponentially, with an added short T₂ component of 20 ms for adenosine monophosphate, resulting in values of 199 ± 8 and 239 ± 14 ms, respectively. The transverse relaxation time for glycerophosphocholine (GPC) was also fitted bi‐exponentially, with an added short T₂ component of 20 ms for glycerophosphatidylethanolamine, which resonates at a similar frequency, resulting in a value of 177 ± 6 ms. Transverse relaxation times for inorganic phosphate, γ‐ATP and glycerophosphatidylcholine mobile phospholipid were fitted mono‐exponentially, resulting in values of 180 ± 4, 19 ± 3 and 20 ± 4 ms, respectively. Coefficients of variation for the duplicate determinations of ¹H total choline (tChol) and the ³¹P metabolites were calculated for the group of volunteers. The reproducibility of inorganic phosphate, the sum of phosphomonoesters and the sum of phosphodiesters with ³¹P MRS imaging was superior to the reproducibility of ¹H MRS for tChol. ¹H and ³¹P data were combined to calculate estimates of the absolute concentrations of PC, GPC and PE in healthy fibroglandular tissue, resulting in upper limits of 0.1, 0.1 and 0.2 mmol/kg of tissue, respectively.     

Effect of phosphate electrolyte buffer on the dynamics of water in tendon and cartilage

A number of NMR spectroscopic and microscopic MRI (microMRI) techniques were used to study proton dynamics in canine tendon and articular cartilage immersed in normal saline solution (NaCl solution) and high-concentration phosphate-buffered saline (PBS) solution. In a proton CPMG experiment on tendons, the T(2) relaxation of the tissue was found to be anisotropic and had two populations. When immersed in saline, the T(2) values were short and their relative populations were anisotropic. When immersed in PBS, the T(2) values increased and their relative populations became isotropic. These phenomena, also verified by proton double-quantum-filtered (DQF) NMR spectroscopy, were interpreted as the catalyzing effect of phosphate ions on proton exchange between water molecules. In the experiment on articular cartilage, the immersion of cartilage-bone blocks in PBS resulted in a significant reduction in the laminar appearance of cartilage on MRI (the magic angle effect). The quantitative T(2) anisotropy by microMRI at 13 microm pixel resolution and DQF NMR spectroscopy confirmed the substantial effect of PBS on the water dynamics in cartilage tissue blocks. This preliminary study has two important implications. For in vitro cartilage research, this work confirms the importance of the salt solution in which the specimen is stored - not all salts have the same effect on the measurable quantities in NMR and MRI. For in vivo cartilage diagnosis, especially using whole-body MRI scanners, this work suggests the possibility of using a suitable electrolyte as a novel contrast agent to assess the ultrastructural changes in cartilage due to tissue degradation.     

Achilles tendon loading during walking: application of a novel optic fiber technique

An optic fiber (Ø 0.5?mm) was utilized for the study of Achilles tendon forces (ATF) in eight volunteers who walked over a 10?m force platform at three speeds (1.1?±?0.1?m?×?s^?1, 1.5?±?0.1?m?×?s^?1 and 1.8?±?0.2?m?×?s^?1). The presented ATF-time curves showed great intersubject variation in magnitudes of the sudden release of force after initial contact and in the peak ATF's (1430?±?500?N). This intersubject variation in the peak force decreased only by 4% when cross-sectional area of the tendon was considered. Measured ground reaction forces and plantar pressures confirmed that the subjects walked quite normally during recordings. The peak ATF was found to be rather insensitive to speed in contrast to the rate of ATF development which increased 32% (?p?相似文献   

短T2组织磁共振成像技术研究进展

常规磁共振有较好的软组织对比度,但对骨、关节、软骨、肌腱等短T2组织（约小于10 ms）的分辨能力欠佳。可通过 增强短T2组织的图像对比度（利用魔角效应和注射造影剂）、开发专用的短T2组织成像技术（可变回波时间成像、超短回波 时间成像和零回波时间成像）和抑制周围长T2组织来获得较高质量的短T2组织图像。近年来,定量磁共振成像技术因其 能精准地反映与病变相关的生化参数特征也被应用于短T2组织病变的临床诊断。本研究主要从增强短T2组织对比度、缩 短序列回波时间和长T2组织抑制等3个方面回顾了短T2组织磁共振成像的常规方法,并对短T2组织的定量磁共振成像技 术进行了系统的分析和展望。     

Doubly selective multiple quantum chemical shift imaging and T1 relaxation time measurement of glutathione (GSH) in the human brain in vivo

Mapping of a major antioxidant, glutathione (GSH), was achieved in the human brain in vivo using a doubly‐selective multiple quantum filtering based chemical shift imaging (CSI) of GSH at 3 T. Both in vivo and phantom tests in CSI and single voxel measurements were consistent with excellent suppression of overlapping signals from creatine, γ‐Amino butyric acid (GABA) and macromolecules. GSH concentration in the fronto‐parietal region was 1.20 ± 0.16 µmol/g (mean ± SD, n = 7). The longitudinal relaxation time (T₁) of GSH in the human brain was 397 ± 44 ms (mean ± SD, n = 5), which was substantially shorter than that of other metabolites. This GSH‐CSI method permits us to address regional differences of GSH in the human brain under conditions where oxidative stress has been implicated, including multiple sclerosis, aging and neurodegenerative diseases. Copyright © 2012 John Wiley & Sons, Ltd.     

Rapid response to and long-term effectiveness of anti-CD20 antibody in conventional therapy resistant Graves’ orbitopathy: A five-year follow-up study

Abstract

The aim of this investigations was to study the effectiveness of anti-CD20 antibody therapy in Graves’ orbitopathy (GO) resistant to glucocorticoids. Five patients were entered in the study. The protocol required no improvement of orbital status after a recent course of glucocorticoids. Activity of GO was confirmed by three independent techniques: clinical activity score (CAS), ^99mTc-labeled diethylene triamine pentaacetic acid (^99mTc DTPA) single photon emission computed tomography and magnetic resonance imaging. Rituximab (RTX) was given as weekly infusions of 375?mg/m² body surface area for four weeks. The mean follow-up period was 67 (range 58–81) months. Improvement of GO has been observed in all patients: CAS before therapy was 6.5?±?1.7 and decreased to 3.4?±?1.6 by one month (p?<?0.05) and remained unchanged (3.2?±?1.7) at 12 months. No further CAS change, in either direction, was detected during the yearly follow-up visits. The mean DTPA uptake before therapy was 16.52?±?4.51?MBq/cm³ and decreased to 11.97?±?2.36?MBq/cm³ at one year (p?<?0.002). The mean of T2 relaxation times before and one year after therapy were 96.91?±?17.61?ms and 84.29?±?9.41?ms, respectively (p?<?0.001). The mean serum TSH receptor antibody (TRAb) levels before therapy, at the one month and one year control visits were 7.4?±?3.4?U/L, 5.6?±?4.5?U/L and 1.7?±?1.5?U/L, respectively (p?<?0.004). No correlation between changes of TRAb and activity parameters has been found. Anti-CD20 treatment seems to influence positively the clinical course of GO, and this effect seems to be stable for five years. To our knowledge, this is the longest published follow-up of RTX treatment in GO.     

Comparison of T1 relaxation times in adipose tissue of severely obese patients and healthy lean subjects measured by 1.5 T MRI

Subcutaneous (SAT) and visceral adipose tissue (VAT) differ in composition, endocrine function and localization in the body. VAT is considered to play a role in the pathogenesis of insulin resistance, type 2 diabetes, fatty liver disease, and other obesity‐related disorders. It has been shown that the amount, distribution, and (cellular) composition of adipose tissue (AT) correlate well with metabolic conditions. In this study, T₁ relaxation times of AT were measured in severely obese subjects and compared with those of healthy lean controls. Here, we tested the hypothesis that T₁ relaxation times of AT differ between lean and obese individuals, but also between VAT and SAT as well as superficial (sSAT) and deep SAT (dSAT) in the same individual. Twenty severely obese subjects (BMI 41.4 ± 4.8 kg/m²) and ten healthy lean controls matched for age (BMI 21.5 ± 1.9 kg/m²) underwent MRI at 1.5 T using a single‐shot fast spin‐echo sequence (short‐tau inversion recovery) at six different inversion times (T_I range 100–1000 ms). T₁ relaxation times were computed for all subjects by fitting the T_I‐dependent MR signal intensities of user‐defined regions of interest in both SAT and VAT to a model function. T₁ times in sSAT and dSAT were only measured in obese patients. For both obese patients and controls, the T₁ times of SAT (275 ± 14 and 301 ± 12 ms) were significantly (p < 0.01) shorter than the respective values in VAT (294 ± 20 and 360 ± 35 ms). Obese subjects also showed significant (p < 0.01) T₁ differences between sSAT (268 ± 11 ms) and dSAT (281 ± 19 ms). More important, T₁ differences in both SAT and VAT were highly significant (p < 0.001) between obese patients and healthy subjects. The results of our pilot study suggest that T₁ relaxation times differ between severely obese patients and lean controls, and may potentially provide an additional means for the non‐invasive assessment of AT conditions and dysfunction. Copyright © 2014 John Wiley & Sons, Ltd.