UTE-MRI常用技术在软骨定量研究中的应用进展

骨关节炎（OA）最初的病理生理变化主要发生在以短T₂成分为主的关节软骨,其信号衰减较快,因此常规MRI序列对早期OA的研究价值有限。MR超短回波时间（UTE）序列可以对软骨进行全面的定量评估。就UTE-T₂* mapping、UTE Adibatic-T_1ρ、UTE-磁化传递（MT）以及酸性化学交换饱和转移（acidoCEST）-UTE等软骨成分定量研究技术的基本原理、优缺点及其应用进展进行综述。     

UTE的基本原理及在骨关节系统中的应用进展

骨关节系统主要由短T_2组织构成,在常规MRI检查中常表现为低信号或无信号。超短回波时间(UTE)序列是研究短T_2组织最常用的成像技术,短T_2组织在UTE影像上表现为高信号。对UTE成像技术的基本原理进行介绍,并综述其在骨皮质、骨膜、肌腱和韧带、关节软骨和半月板中的具体应用。     

三角纤维软骨的超短回波时间(UTE)定量MR成像:摆位的差异

正摘要目的比较分别在中立位、腕部尺骨屈曲和前臂内旋位获得的三角纤维软骨(TFC)超短时间回波(UTE)的T_2*值。方法对10名健康志愿者使用8通道膝关节线圈在3T     

超短回波时间MR成像对髌骨的双组分分析:组织病理与偏振光镜结果的关系

摘要目的通过超短回波时间(TE)MR成像,使用半定量组织病理学及偏振光镜(PLM)技术评价人类尸体髌骨软骨,得出短T2*及长T2*水成分的关系。材料与方法得到临床评估委员会同意后,我们使用超短回波时间MR成像、自旋回波成像、组织病理分析及PLM来评估20例人类尸体髌骨。通过对超短-TE信号衰减使用双组分适应,我们分析了每个髌骨短T2*及长T2*水成分。     

3.0T MRI T_2~* mapping评估儿童血友病性关节病膝关节软骨的价值

目的探讨磁共振T_2~* mapping成像技术在儿童血友病性关节病(hemophilic arthropathy, HA)膝关节软骨损伤的诊断价值。方法采用西门子Skyra 3.0T MRI对19例HA患儿组、15例正常组儿童膝关节行MRI扫描,行T_2~* mapping序列扫描,并测量T_2~*值。比较患儿组T_2~* mapping、T_1WI-SE、T_2WI-TSE-FS序列所测量的关节内含铁血黄素沉积。T_2~* mapping序列扫描后在工作站分别测量膝关节研究髌骨、股骨远端内侧髁(承重区、后部非承重区)、股骨远端外侧髁(承重区、前后部非承重区)、胫骨内、外侧平台面8处软骨T_2~* mapping成像的T_2~*值,比较两组膝关节T_2~*值的差异。另对关节内含铁血黄素在T_2~* mapping、T_1WI-SE、T_2WI-TSE-FS三个序列中分别测量最大截面,比较这三个序列在评估血友病性关节病含铁血黄素沉积显示结果的差异,P0.05具有统计学意义。结果血友病性关节病患者膝关节髌骨软骨平均T_2~*值(31.6±12.5)ms,股骨远端内侧髁承重区、后部非承重区软骨平均T_2~*值分别为(29.4±10.0)ms、(34.1±9.7)ms,股骨远端外侧髁承重区、前部、后部非承重区软骨平均T_2~*值分别为(33.7±9.8)ms、(35.6±12.2)ms、(37.2±11.2)ms,内、外侧胫骨平台面软骨平均T_2~*值(30.2±7.9)ms、(28.0±8.7)ms。股骨外侧髁、股骨内侧髁后部非承重区、胫骨平台内外侧与健康组T_2~*平均值比较,差异具有统计学意义(P0.05)。股骨内侧髁承重区、髌骨软骨与健康组T_2~*平均值比较无统计学意义(P0.05)。T_2~* mapping、T_1WI-SE、T_2WI-TSE-FS三个序列最大截面显示含铁血黄素沉积分别是(142.0±137.9)mm~2、(114.8±111.4)mm~2、(115.6±115.3)mm~2,差异不具有统计学意义。结论磁共振T_2~* mapping序列通过T_2~*值的测量,能定量的反应膝关节血友病性关节病早期的损伤、变性。     

骨关节炎软骨损伤的影像学研究进展

骨关节炎(OA)是中老年人最常见的退行性骨关节病,常表现为关节疼痛、畸形和功能障碍, 严重影响患者的生活质量.其发病核心环节是关节软骨的损伤改变.目前,常规影像技术局限于诊断晚期关节软骨的形态改变.随着一批MR新技术[关节软骨延迟增强磁共振成像(delayed gadolinium-enhanced MRI of cartilage,dGEMRIC)、T2释放时间成像(T2 relaxation time mapping)、T1ρ释放时间成像、化学交换饱和转移(chemical exchange saturation transfer,CEST)成像、超短回波时间(ultrashort echo time,UTE)成像、Na23 MRI]、光学相干断层成像(optical coherence tomography,OCT)、SPECT/CT的发展为软骨损伤提供了更准确客观的评价方法,可以在软骨病变早期阶段观察软骨微小的形态改变,以及形态尚未改变之前的生化成分、代谢改变观察软骨的变化,对病程进行评估并更早辅助临床进行早期干预.本文旨在回顾各技术的成像原理及相关生化联系,并讨论各自的优缺点,更好地了解软骨影像学评价的最新进展及其在临床的运用.     

使用3.0T磁共振成像技术二维反转恢复超短回波时间和三维超短回波时间对半月板钙化形态和定量评价的可行性研究

摘要目的评价超短回波时间(UTE)MRI技术对不同类型半月板钙化的形态评估效果,将这些序列与标准的临床序列进行比较并测量半月板钙化的T2*值。方法该研究由机构审查委员会豁免,知情同意不是必需的。10具尸体的半月板行高空间分辨力X线摄影和3.0T的磁共振形态成像[T1加权快速自旋回波序列(FSE),T2加权FSE序列,质子密度加权(PD)的FSE序列,二维(2D)快速毁损梯度回波序列(FSPGR),三维(3D)FSPGR序列和3DUTE序列]以及定量成像[2D反转恢复(IR)UTE序列和3DUTE序列]。     

MRI三维超短回波时间双回波脉冲序列在骨与关节成像中的初步应用

目的 探讨MR三维超短回波时间(UTE)的双回波脉冲序列成像在骨与关节中的应用.方法 分别对7名健康志愿者和1名可疑左膝关节外侧半月板撕裂志愿者的胫骨干、膝关节、踝关节、腕关节及一段离体猪腓骨行MR三维UTE的双回波脉冲序列成像.将原始双回波图及多平面重组后的双回波图的前后2个回波相减获得相减后的差异图,比较2种图像处理方法的信噪比.将踝关节跟腱的UTE双回波成像的第1个回波时间(TE1)分别设置为0.08、0.16、0.24、0.35 ms,对比不同TE1时间2个原始回波相减所得的差异图的图像质量.对踝关节肌腱的TE1为0.08 ms的原始回波图相减后的差异图行最大强度投影获得肌腱的三维空间图.对获取的数据进行单因素方差分析和配对资料t检验.结果 通过对原始回波图相减后的差异图行最大强度投影显示了肌腱的三维空间分布图.8名志愿者的骨皮质、骨膜、肌腱和半月板在超短TE的双回波脉冲序列成像上表现为高信号.将原始双回波图(信噪比为2.82±0.75)行多平面重组后再减影(信噪比为3.76±0.88)可增加图像信噪比(t=-4.851,P<0.01).踝关节跟腱的不同TEl成像的图像质量不同,TE1为0.08 mg的图像质量最高,在TE1分别为0.08、0.16、0.24、0.35 ms时,对比噪声比分别为1.74±0.54、1.35±0.60、1.20±0.48、0.89±0.24,差异有统计学意义(F=3.681,P<0.05).随着成像时间的延长,伪影逐渐增多.结论 三维超短TE的双回波成像能显示传统的临床MR成像序列不能显示的主要含短T2成分的组织,为对这些组织的进一步量化研究奠定了基础.     

颅内出血性病变:用0.5T和1.5T SE和GR MRI的评价

作者对20例典型的颅内出血(50处病变)的MR表现作3回顾性分析。MRI使用两种场强(0.5T和1.5T)、SE(自旋回波序列)和GR(梯度聚焦回波序列)T_2加权。两种场强的SE T_2加权TR/TE均为500/30,T_2加权TR/TE为250/30,60,层厚在0.5T和1.5T分别为8mm和7mm,层面间隔为层厚的10%;两种场强的GR T_2~*加权TR/TE均为500/35,层厚10mm,使用35°翻转角。根据两种场强三种序列的检查所见,作者认     

超短TE MRI对深部软骨的评估（25例尸体髌软骨MRI和组织学对比研究）

目的：利用超短TE成像技术对常规MR成像序列难以显示的深部关节软骨进行定性和定量研究。方法：用装有超短TE软件的1．5T MR机对25例尸体髌软骨标本进行MR扫描，扫描序列包括标准T1WI、脂肪抑制PdWI序列、超短TE成像（TE80ms）。将所有标本均连续切成3mm层厚断面并对每个断面进行大体和组织学分析。     

Ultrashort echo time imaging with bicomponent analysis

Biological tissues frequently contain different water compartments, and these often have distinct transverse relaxation times. Quantification of these may be problematic on clinical scanners because spin echo sequences usually have initial echo times that are too long to accurately quantify shorter relaxation time components. In this study, an ultrashort echo time pulse sequence was used together with bicomponent analysis to quantify both the short and long T(2) components in tissues of the musculoskeletal system. Feasibility studies were performed using numerical simulation, and on phantoms and in vitro tissues including bovine cortical bone, ligaments, menisci, tendons, and articular cartilage. The simulation and phantom studies demonstrated that this technique can quantify T(2) * and fractions of the short and long T(2) components. The tissues studies showed two distinct components with short T(2) *s ranging from 0.3 ms for bovine cortical bone to 2.1 ms for menisci, and long T(2) *s ranging from 2.9 ms for bovine cortical bone to 35.0 ms for articular cartilage. The short T(2) * fraction ranged from 18.5% for patella cartilage to 80.9% for ligaments. The results show that ultrashort echo time imaging with bicomponent analysis can quantify the short and long T(2) water components in vitro in musculoskeletal tissues.     

MRI超短回波时间序列评价膝关节半月板的研究进展

半月板是膝关节的重要结构,MRI超短回波时间（UTE）序列相比传统MRI序列能够直接采集短T₂/T₂*信号,不仅能够定量测量半月板,还能够显示半月板胶原纤维及钙化成分,区分半月板红白区,以及评估半月板pH值等。简要介绍UTE序列,并就其在半月板中的研究进展予以综述。     

Magnetic resonance imaging of the Achilles tendon using ultrashort TE (UTE) pulse sequences

AIM: To assess the potential value of imaging the Achilles tendon with ultrashort echo time (UTE) pulse sequences. MATERIALS AND METHODS: Four normal controls and four patients with chronic Achilles tendinopathy were examined in the sagittal and transverse planes. Three of the patients were examined before and after intravenous gadodiamide. RESULTS: The fascicular pattern was clearly demonstrated within the tendon and detail of the three distinct fibrocartilaginous components of an "enthesis organ" was well seen. T2* measurements showed two short T2* components. Increase in long T2 components with reduction in short T2 components was seen in tendinopathy. Contrast enhancement was much more extensive than with conventional sequences in two cases of tendinopathy but in a third case, there was a region of reduced enhancement. CONCLUSION: UTE pulse sequences provide anatomical detail not apparent with conventional sequences, demonstrate differences in T2* and show patterns of both increased and decreased enhancement in tendinopathy.     

Characterization of proteoglycan depletion in articular cartilage using two-dimensional time domain nuclear magnetic resonance.

In vitro proteoglycan (PG) depletion in the 20-40% range (enzymatic PG depletion of normal cartilage in the early osteoarthritis (OA) PG depletion range) was investigated in articular cartilage using 2D time domain NMR relaxation techniques. Spin-lattice relaxation times were measured at low fields (T(1rho)) and at high fields (T(1)) using nonselective and selective excitation pulse sequences. The short relaxation time magnetization components in T(1rho) ( approximately 8% signal) and nonselective T(1) ( approximately 5% signal) experiments were significantly altered with PG degradation. In addition, a magnetization component ( approximately 5% signal) with a "fast " T(1) approximately 7 ms was observed in the T(1) experiment involving selective excitation. This fast T(1) was at least 10 times shorter than the short T(1) in the nonselective experiment and was associated with a strong magnetization exchange mechanism between collagen and PG. The results suggest that T(1rho) and T(1) (nonselective and selective) relaxation based MRI techniques, which focus on the short relaxation time magnetization components, have the potential of detecting molecular abnormalities associated with early OA earlier than single, long relaxation time component approaches.     

Reversed laminar appearance of articular cartilage by T1‐weighting in 3D fat‐suppressed spoiled gradient recalled echo (SPGR) imaging

Purpose:

To investigate the reversed intensity pattern in the laminar appearance of articular cartilage by 3D fat‐suppressed spoiled gradient recalled echo (FS‐SPGR) imaging in magnetic resonance imaging (MRI).

Materials and Methods:

The 3D SPGR experiments were carried out on canine articular cartilage with an echo time (TE) of 2.12 msec, a repetition time (TR) of 60 msec, and various flip angles (5° to 80°). In addition, T1, T2, and T2* in cartilage were imaged and used to explain the laminar appearance in SPGR imaging.

Results:

The profiles of T2 and T2* in cartilage were similar in shape. However, the T2 values from the multigradient‐echo imaging sequence were about 1/3 of those from single spin‐echo sequences at a pixel resolution of 26 μm. While the laminar appearance of cartilage in spin‐echo imaging is caused mostly by T2‐weighting, the laminar appearance of cartilage in fast imaging (ie, short TR) at the magic angle can have a reversed intensity pattern, which is caused mostly by T1‐weighting.

Conclusion:

The laminar appearance of articular cartilage can have opposite intensity patterns in the deep part of the tissue, depending on whether the image is T1‐weighted or T2‐weighted. The underlying molecular structure and experimental protocols should both be considered when one examines cartilage images in MRI. J. Magn. Reson. Imaging 2010;32:733–737. © 2010 Wiley‐Liss, Inc.     

T2* measurement of the knee articular cartilage in osteoarthritis at 3T

Purpose:

To measure reproducibility, longitudinal and cross‐sectional differences in T2* maps at 3 Tesla (T) in the articular cartilage of the knee in subjects with osteoarthritis (OA) and healthy matched controls.

Materials and Methods:

MRI data and standing radiographs were acquired from 33 subjects with OA and 21 healthy controls matched for age and gender. Reproducibility was determined by two sessions in the same day, while longitudinal and cross‐sectional group differences used visits at baseline, 3 and 6 months. Each visit contained symptomological assessments and an MRI session consisting of high resolution three‐dimensional double‐echo‐steady‐state (DESS) and co‐registered T2* maps of the most diseased knee. A blinded reader delineated the articular cartilage on the DESS images and median T2* values were reported.

Results:

T2* values showed an intra‐visit reproducibility of 2.0% over the whole cartilage. No longitudinal effects were measured in either group over 6 months. T2* maps revealed a 5.8% longer T2* in the medial tibial cartilage and 7.6% and 6.5% shorter T2* in the patellar and lateral tibial cartilage, respectively, in OA subjects versus controls (P < 0.02).

Conclusion:

T2* mapping is a repeatable process that showed differences between the OA subject and control groups. J. Magn. Reson. Imaging 2012;35:1422–1429. © 2012 Wiley Periodicals Inc.     

Contrast enhancement of short T2 tissues using ultrashort TE (UTE) pulse sequences

AIM: To review the effects of contrast administration on tissues with short T2s using a pulse ultrashort echo time (UTE) sequence. MATERIALS AND METHODS: Pulse sequences were implemented with echo times of 0.08 ms and three later gradient echoes. A fat-suppression option was used and later echo images were subtracted from the first echo image. Contrast enhancement with gadodiamide (0.3 mmol/kg) was used for serial studies in a volunteer. The images of 10 patients were reviewed for evidence of contrast enhancement in short T2 tissues. RESULTS: Contrast enhancement was seen in normal meninges, falx, tendons, ligaments, menisci, periosteum and cortical bone. In addition more extensive enhancement than with conventional pulse sequences was seen in meningeal disease, intervertebral disc disease, periligamentous scar tissue and periosteum after fracture. Subtraction of an image taken with a longer TE from the first image was of value in differentiating enhancement in short T2 tissues from that in long T2 tissues or blood. CONCLUSION: Contrast enhancement can be identified in tissues with short T2s using UTE pulse sequences in health and disease.     

UTE imaging in the musculoskeletal system

Tissues, such as bone, tendon, and ligaments, contain a high fraction of components with "short" and "ultrashort" transverse relaxation times and therefore have short mean transverse relaxation times. With conventional magnetic resonance imaging (MRI) sequences that employ relatively long echo times (TEs), there is no opportunity to encode the decaying signal of short and ultrashort T₂/T₂* tissues before it has reached zero or near zero. The clinically compatible ultrashort TE (UTE) sequence has been increasingly used to study the musculoskeletal system. This article reviews the UTE sequence as well as various modifications that have been implemented since its introduction. These modifications have been used to improve efficiency or contrast as well as provide quantitative analysis. This article reviews several clinical musculoskeletal applications of UTE. J. Magn. Reson. Imaging 2015;41:870–883 . © 2014 Wiley Periodicals, Inc .