Selective water excitation for faster MR imaging of articular cartilage defects: initial clinical results

Our objective was to compare a water-excitation (WE) 3D fast low-angle shot (FLASH) MR sequence for faster imaging of articular cartilage defects of the knee to a conventional fat-saturated (FS) 3D FLASH MR sequence. This prospective study included 16 knees of 16 patients with suspected cartilage lesions. The MR imaging in transverse and sagittal planes included (a) FS 3D FLASH (TR/TE: 45 ms/11 ms, scan time 8 min, flip angle 50°), and (b) WE 3D FLASH (TR/TE: 28 ms/11 ms, scan time 4 min 58 s, flip angle 40°). For each sequence signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were quantified. The detected cartilage lesions were evaluated using a semi-quantitative four-scale scoring system (grades 0–III). The data were compared between the sequences using the paired Student's t-test. No statistically significant differences between the sequences were found for SNR, CNR, and cartilage defect grading (p=0.14–0.8). The WE 3D FLASH MR imaging seems to be promising for fast imaging of articular cartilage lesions of the knee. Electronic Publication     

膝关节软骨MR成像的技术探讨

目的探讨膝关节软骨MR I成像技术和三维(3D)软骨重建的方法,为临床早期诊断和治疗方法提供了有效的评估方法。方法对90例膝关节外伤、关节炎性病变患者和10例健康志愿者进行MR I扫描,采取常规和特殊的二维(2D)、3D多序列,多参数的比较。对3D快速梯度回波扫描序列获得膝关节各关节软骨3D图像,利用最大信号强度投影法(M IP)进行3D重建。对各关节软骨的平均厚度的测量值进行统计学分析。结果膝关节软骨MR I成像技术和3D软骨重建的方法,可以清晰显示膝关节各关节软骨的结构,在2D FSE序列上关节软骨约50%均显示为3层改变,在3D重建图像上,可清淅地多角度整体显示膝关节各关节软骨的结构,空间分辨率高。结论膝关节软骨MR I成像和3D软骨重建技术,为临床早期诊断和治疗方法提供帮助。     

Comparison of new sequences for high-resolution cartilage imaging.

The high prevalence of osteoarthritis continues to demand improved accuracy in detecting cartilage injury and monitoring its response to different treatments. MRI is the most accurate noninvasive method of diagnosing cartilage lesions. However, MR imaging of cartilage is limited by scan time, signal-to-noise ratio (SNR), and image contrast. Recently, there has been renewed interest in SNR-efficient imaging sequences for imaging cartilage, including various forms of steady-state free-precession as well as driven-equilibrium imaging. This work compares several of these sequences with existing methods, both theoretically and in normal volunteers. Results show that the new steady-state methods increase SNR-efficiency by as much as 30% and improve cartilage-synovial fluid contrast by a factor of three. Additionally, these methods markedly decrease minimum scan times, while providing 3D coverage without the characteristic blurring seen in fast spin-echo images.     

High-resolution ultrashort echo time (UTE) imaging on human knee with AWSOS sequence at 3.0 T

Purpose:

To demonstrate the technical feasibility of high‐resolution (0.28–0.14 mm) ultrashort echo time (UTE) imaging on human knee at 3T with the acquisition‐weighted stack of spirals (AWSOS) sequence.

Materials and Methods:

Nine human subjects were scanned on a 3T MRI scanner with an 8‐channel knee coil using the AWSOS sequence and isocenter positioning plus manual shimming.

Results:

High‐resolution UTE images were obtained on the subject knees at TE = 0.6 msec with total acquisition time of 5.12 minutes for 60 slices at an in‐plane resolution of 0.28 mm and 10.24 minutes for 40 slices at an in‐plane resolution of 0.14 mm. Isocenter positioning, manual shimming, and the 8‐channel array coil helped minimize image distortion and achieve high signal‐to‐noise ratio (SNR).

Conclusion:

It is technically feasible on a clinical 3T MRI scanner to perform UTE imaging on human knee at very high spatial resolutions (0.28–0.14 mm) within reasonable scan time (5–10 min) using the AWSOS sequence. J. Magn. Reson. Imaging 2012;35:204‐210. © 2011 Wiley Periodicals, Inc.     

3.0 T MR SPACE序列与传统关节软骨三维成像序列比较研究

目的通过比较软骨信号噪声比(SNR)和对比噪声比(CNR),分析临床三维MR序列显示软骨的效果。资料与方法选取25名健康志愿者进行软骨MRI(年龄21～29岁,平均24岁),使用Siemens Magnetom Trio Tim3.0T超导型磁共振成像仪和膝关节专用线圈。应用:(1)脂肪抑制快速小角度激发(fast low angle shot,FLASH)序列;(2)FLASH序列+水激发(water-excitation,WE);(3)双回波稳态进动(dualecho steady state,DESS)序列;(4)真稳态进动快速成像(true fast imaging with steady-state precession,True-FISP)序列;(5)三维质子加权快速自旋回波(sampling perfection with application-optimized contrast using different flip angle evolutions,SPACE)序列;(6)二维脂肪抑制快速自旋回波质子密度加权成像(fat-suppressed-2D-fast spine cho-pro...     

前交叉韧带斜矢状位MR成像研究

目的观察基于膝关节MR 2DT2WI+fs图像的重建图像对前交叉韧带显示效果,优化扫描程序。方法分析60例前交叉韧带MR检查图像,按检查方法分A、B、C三组进行观察分析。A组:常规扫描标准矢状位图像;B组:基于A组图像的斜矢状位重建图像;C组:斜矢状位扫描图像。观察三组图像对前交叉韧带的显示情况。将图像分二级进行评价:Ⅰ级为前交叉韧带1幅图像完整、清晰显示;Ⅱ级前交叉韧带1幅图像不能完整显示,需连续两幅或三幅图像才能完整显示;最后统计数据进行分析。结果 A组图像:Ⅰ级36例,占60%;Ⅱ级24例,占40%。B组图像:Ⅰ级56例,占93.3%;Ⅱ级4例,占6.7%。C组图像:Ⅰ级5 4例,占90%;Ⅱ级6例,占10%。经计算显示A、B两组图像具显著差异;A、C两组图像具显著差异;B、C两组图像无显著差异。结论基于前交叉韧带MR2DT2WI+fs图像的重建图像对其显示良好,建议膝关节磁共振检查时以标准矢状位扫描所得二维图像进行MPR重建观察,无须特意行斜矢状位扫描或三维成像扫描后重建,可以优化MR检查流程。     

Parallel imaging of knee cartilage at 3 Tesla

PURPOSE: To evaluate the feasibility and reproducibility of quantitative cartilage imaging with parallel imaging at 3T and to determine the impact of the acceleration factor (AF) on morphological and relaxation measurements. MATERIALS AND METHODS: An eight-channel phased-array knee coil was employed for conventional and parallel imaging on a 3T scanner. The imaging protocol consisted of a T2-weighted fast spin echo (FSE), a 3D-spoiled gradient echo (SPGR), a custom 3D-SPGR T1rho, and a 3D-SPGR T2 sequence. Parallel imaging was performed with an array spatial sensitivity technique (ASSET). The left knees of six healthy volunteers were scanned with both conventional and parallel imaging (AF = 2). RESULTS: Morphological parameters and relaxation maps from parallel imaging methods (AF = 2) showed comparable results with conventional method. The intraclass correlation coefficient (ICC) of the two methods for cartilage volume, mean cartilage thickness, T1rho, and T2 were 0.999, 0.977, 0.964, and 0.969, respectively, while demonstrating excellent reproducibility. No significant measurement differences were found when AF reached 3 despite the low signal-to-noise ratio (SNR). CONCLUSION: The study demonstrated that parallel imaging can be applied to current knee cartilage quantification at AF = 2 without degrading measurement accuracy with good reproducibility while effectively reducing scan time. Shorter imaging times can be achieved with higher AF at the cost of SNR.     

Imaging of the articular cartilage in osteoarthritis of the knee joint: 3D spatial-spectral spoiled gradient-echo vs. fat-suppressed 3D spoiled gradient-echo MR imaging

PURPOSE: To compare three-dimensional (3D) spatial-spectral (SS) spoiled gradient-recalled acquisition in the steady state (SPGR) imaging with fat-suppressed 3D SPGR sequences in MR imaging of articular cartilage of the knee joint in patients with osteoarthritis. MATERIALS AND METHODS: MR images of six patients with osteoarthritis of the knee were prospectively examined with a 1.5T MR scanner. For quantitative analyses, the signal-to-noise ratios, contrast-to-noise ratios, and contrast of cartilage and adjacent structures including meniscus, synovial fluid, muscle, fat tissue, and bone marrow were measured. RESULTS: In patients with osteoarthritis, 3DSS-SPGR images demonstrated higher spatial resolution and higher mean signal-to-noise (S/N) ratios (cartilage, 24.9; synovial fluid, 12.3; muscle, 20.7; meniscus, 21.6), with shorter acquisition times (7 minutes 20 seconds), when compared to fat-suppressed 3D SPGR images (cartilage, 22.3; synovial fluid, 10.8; muscle, 16.7; meniscus, 13.4). CONCLUSION: 3DSS-SPGR imaging is a promising method for evaluating cartilage pathology in patients with osteoarthritis of the knee and has the potential to replace fat-suppressed 3D SPGR imaging.     

Projection extension for region of interest imaging in cone-beam CT

RATIONALE AND OBJECTIVES: For 3D X-ray imaging during interventions, changes of the imaged object are often restricted to a small part of the field of view, suggesting region of interest (ROI) imaging by irradiating this area only. In this article, we present a novel method for extension of truncated projections in order to avoid truncation artifacts in C-arm based 3D ROI imaging. MATERIALS AND METHODS: The method makes use of prior knowledge by combining forward projections of a previously acquired, nontruncated 3D reference image with the truncated ROI projections. Rigid registration between the two datasets is achieved by using a technique based on local cross-correlation. To account for a gray value mismatch between the two data sets due to, e.g., differing beam quality and different contributions of scattered radiation, a linear gray level transformation is applied to the forward-projected reference data. RESULTS: The performance of different gray value transformation schemes is systematically assessed by means of numerical simulations. For various simulated scenarios, the best performing transformation has been identified, providing practical guidelines for selecting a scheme depending on the origin of the gray-level mismatch. Experiments prove the high performance of the developed method. CONCLUSION: The presented technique enables almost artifact-free 3D ROI imaging during interventions. This actually allows for repeated scans at low dose and enables intraprocedural imaging of large objects even with a small detector. However, applicability of the method is limited to scenarios where direct access to a reference image, e.g., a prior CT scan, is available.     

Routine MR examination of the knee using parallel imaging

AIM: To demonstrate the feasibility and the clinical value of parallel imaging of the knee. METHODS: A pair of flex coils was used for the parallel imaging. Before optimization of the protocol, qualitative and quantitative analysis was performed by volunteer and phantom study. Two separate consecutive groups of 80 patients were examined with or without parallel imaging and compared with the arthroscopic results. RESULTS: Parallel imaging obtained a total of 164 images of six series in less than 20 min. Compared with conventional imaging, the parallel imaging appeared slightly noisy with an 83% relative signal-to-noise ratio. Demarcation of the cruciate ligaments and menisci were rated equivalent. For the patients study, the parallel imaging delineated ligament and meniscus pathologies with accuracies of over 93%. CONCLUSION: Parallel MR imaging of the knee enables significant reduction of scan time as well as preserving diagnostic results.     

Signal‐to‐noise optimization for sodium MRI of the human knee at 4.7 Tesla using steady state

Sodium magnetic resonance imaging of knee cartilage is a possible diagnostic method for osteoarthritis, but low signal‐to‐noise ratio yields low spatial resolution images and long scan times. For a given scan time, a steady‐state approach with reduced repetition time and increased averaging may improve signal‐to‐noise ratio and hence attainable resolution. However, repetition time reduction results in increased power deposition, which must be offset with increased radiofrequency pulse length and/or reduced flip angle to maintain an acceptable specific absorption rate. Simulations varying flip angle, repetition time, and radiofrequency pulse length were performed for constant power deposition corresponding to ～6 W/kg over the human knee at 4.7T. For 10% agar, simulation closely matched experiment. For healthy human knee cartilage, a 37% increase in signal‐to‐noise ratio was predicted for steady‐state over “fully relaxed” parameters while a 29% ± 4% increase was determined experimentally (n = 10). Partial volume of cartilage with synovial fluid, inaccurate relaxation parameters used in simulation, and/or quadrupolar splitting may be responsible for this disagreement. Excellent quality sodium images of the human knee were produced in 9 mins at 4.7T using the signal‐to‐noise ratio enhancing steady‐state technique. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

正常成年人膝关节软骨的MR多序列比较研究

目的　探讨正常成年人膝关节软骨的多序列MR表现及厚度 ,比较其优缺点。方法　选取健康成年志愿者 3 0名 ,男 18名 ,女 12名 ,分别计算并比较T1 WI、T2 WI、PDWI、短 -TI反转恢复序列 (STIR)和三维脂肪抑制扰相梯度回波序列 (3D -FS -SPGR)关节软骨同生理盐水、骨髓和肌肉的对比度噪声比 (CNR) ,观察各序列软骨的MR表现、三维重建并测量软骨厚度。结果　 3D -FS -SPGR序列关节软骨同生理盐水、骨髓和肌肉的CNR值均与其他序列有显著性差异 ;T1 WI和PDWI序列关节软骨约 5 0 % (13 5 0 )表现为 3层改变 ,T2 WI和STIR序列则均表现为单层改变 ,3D -FS -SPGR序列软骨分层与软骨厚度有关 ,最多可见 5层改变 ;3D -FS-SPGR序列软骨厚度的测量值较其他序列准确 ,本组正常男性与女性膝关节各部位关节软骨的平均厚度分别为 (2 .63± 0 .69)mm和 (2 .5 2± 0 .62 )mm。结论　SE序列 ,特别是T1 WI软骨的分层改变与其组织学结构有关 ,但 3D -FS -SPGR序列软骨的分层是由“截断伪影”所致。 3D -FS -SPGR序列较其他序列有着明显的优势 ,能使关节软骨显示更加清晰 ,厚度测量更加准确 ,结合三维重建技术能为临床诊断与治疗提供更多的信息     

Measurement of tibiofemoral kinematics using highly accelerated 3D radial sampling

This study investigated the use of dynamic, volumetric MRI to measure 3D skeletal motion. Ten healthy subjects were positioned on a MR‐compatible knee loading device and instructed to harmonically flex and extend their knee at 0.5 Hz. The device induced active quadriceps loading with knee flexion, similar to the load acceptance phase of gait. Volumetric images were continuously acquired for 5 min using a 3D cine spoiled gradient‐echo sequence in conjunction with vastly under‐sampled isotropic projection reconstruction. Knee angle was simultaneously monitored and used retrospectively to sort images into 60 frames over the motion cycle. High‐resolution static knee images were acquired and segmented to create subject‐specific models of the femur and tibia. At each time frame, bone positions and orientations were determined by automatically registering the skeletal models to the dynamic images. Three‐dimensional tibiofemoral translations and rotations were consistent across healthy subjects. Internal tibia rotations of 7.8 ± 3.5° were present with 35.8 ± 3.8° of knee flexion, a pattern consistent with knee kinematic measures during walking. We conclude that vastly under‐sampled isotropic projection reconstruction imaging is a promising approach for noninvasively measuring 3D joint kinematics, which may be useful for assessing cartilage contact and investigating the causes and treatment of joint abnormalities. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Preliminary trial of three-dimensional water-excitation magnetization transfer contrast MR imaging of articular cartilage]

MR images of articular cartilage were evaluated with a three-dimensional (3D) water-excitation sequence (repetition time/echo time/flip angle = 28 msec/14 msec/20 degrees) with and without on-resonance magnetization transfer contrast (MTC) pulse in-vitro and in-vivo. 3D water-excitation images with MTC pulse showed a significantly higher contrast-to-noise ratio between normal saline or joint effusion and articular cartilage than images without MTC pulse. In 2 patients with osteoarthritis of the knee, joint effusion showed higher signal intensity than cartilage (arthrogram-like effect) on 3D water-excitation MTC images. The contrast between joint effusion and articular cartilage on 3D water-excitation MTC images was similar to that on fat-suppressed 2D protondensity-weighted fast spin echo images. In conclusion, 3D water-excitation MTC imaging is a promising method by which to evaluate articular cartilage in osteoarthritis and cartilage defect with thin sections and a reasonable scan time.     

显示正常人膝关节软骨分层的最佳MRI序列

目的:显示正常人膝关节软骨分层的最佳MRI序列,为关节病变的早期诊断提供技术支持.方法:选择无膝关节症状的志愿者140例,分别采用SE-T1WI、脂肪抑制二维快速小角度激发(FS -2D-FLASH)和脂肪抑制三维稳态旋进快速成像(FS-3D-FISP)三个扫描序列,行膝关节矢状面扫描.分析显示软骨分层的最佳MRI序列.结果:FLASH序列显示结果为140例中有129例显示膝关节软骨分3层,9例无分层,2例可见分5层,显示分层例数多,分层清楚,扫描时间较短;SE序列140例中有101例显示膝关节软骨分3层,39例无分层,未见分5层者,显示分层例数较少;FISP序列140例中有133例显示膝关节软骨分3层,5例无分层,2例分5层,显示分层例数多,但分层模糊,扫描时间长.结论:FS-FLASH-2D序列是显示膝关节软骨分层的最佳序列.     

正常人膝关节软骨MR成像和软骨重建

目的　研究正常人膝关节软骨的MR成像和软骨三维重建方法 ,为临床诊治关节软骨病变提供科学依据。材料与方法　使用Philips 1.0T磁共振成像仪对 2 0例志愿者行软骨序列扫描 ,然后进行三维软骨重建。 结果　软骨序列及软骨重建技术可以清晰显示软骨的结构 ,关节软骨在SE序列上显示为 3层结构 ,在SPIR/ 3D/FFE/T1WI上最多显示为 4层结构 ,重建后的软骨像具有立体直观的效果 ,并具有良好的空间分辨率。结论　软骨MR成像和软骨重建能清晰显示膝关节的软骨结构 ,可为临床对骨关节病变的诊断和治疗提供帮助。     

Steady-state diffusion-weighted imaging of in vivo knee cartilage.

Diffusion-weighted imaging (DWI) has strong potential as a diagnostic for early cartilage damage, with clinical impact for diseases such as osteoarthritis. However, in vivo DWI of cartilage has proven difficult with conventional methods due to the short T2. This work presents a 3D steady-state DWI sequence that is able to image short-T2 species with high SNR. When combined with 2D navigator correction of motion-induced phase artifacts, this method enables high resolution in vivo DWI of cartilage. In vivo knee images in healthy subjects are presented with high SNR (SNR = 110) and submillimeter in-plane resolution (0.5 x 0.7 x 3.0 mm(3)). A method for fitting the diffusion coefficient is presented which produces fits within 10% of literature values. This method should be applicable to other short-T2 tissues, such as muscle, which are difficult to image using traditional DWI methods.     

Subtraction of in-phase and opposed-phase images in dynamic MR mammography

PURPOSE: To develop and to evaluate an advanced image acquisition and analysis method for collecting T(1)-weighted dynamic 3D MR mammography data sets by using a combined in-phase (IP) and opposed-phase (OP) imaging procedure. MATERIALS AND METHODS: 3D MR mammography data sets were acquired by applying an interleaved gradient-echo OP and IP imaging sequence during administration of contrast agent. A phantom data set, two volunteer breast data sets, and six patient breast data sets were recorded. Subtraction of dynamic in-phase magnitude images was performed for clinical assessment. In addition, the magnitude subtraction (SIPOP) as well as the complex subtraction (cSIPOP) of the IP and OP magnitude and phase images were considered. RESULTS: The detection of small lesions, lesion boundaries, and tumor offshoots in fatty tissue was improved by the subtraction of IP and OP images without the risk of signal cancellation due to partial volume effects. CONCLUSION: Dynamic MR mammography acquisition of IP and OP images in combination with appropriate data processing yields important supplementary information that can support routinely applied diagnostics of breast lesions that are fully embedded in fatty tissue by only marginally increasing acquisition time.     

Three-dimensional MR visualization of the intracisternal course of the cranial nerves V-VIII by virtual cisternoscopy

Purpose:
A post-processing protocol for 3D visualization of the cranial nerves V-VIII along their intracisternal course is presented. Material and Methods:
Six healthy volunteers underwent MR imaging (1.5 T) to obtain high-resolution heavily T2-weighted data sets (3DFT CISS) with isotropic voxels (0.5 mm³). The data sets were post-processed by using volume rendering software in order to visualize the intracisternal courses of the cranial nerves V-VIII as well as their root entry zones. The data acquisition and post-processing protocol was then applied in 14 patients with a suspected neural compression syndrome according to the clinical findings as well as cross-sectional images and evaluated with respect to image quality and diagnostic value by two neuroradiologists, using a five-point scale. Results:
Virtual cisternoscopy allowed a comprehensive intracisternal 3D visualization of the affected cranial nerves in 12/14 patients. The mean post-processing time amounted to 13.1/5.6/13.7 min for the cranial nerves V/VI/VII and VIII. The mean score for image quality was 4.2, that for diagnostic value 4.1. 2D and/or 3D reference images were indispensable for appreciating the spatial information provided by virtual cisternoscopy. Conclusion:
The data acquisition and post-processing protocol presented here allows comprehensive and standardized intracisternal 3D visualization of the cranial nerves V-VIII in a routine setting as a complementary imaging procedure.     

MRI pyschophysics: An experimental framework relating image quality to diagnostic performance metrics

Purpose:

To determine the minimal image quality needed to preserve diagnostic performance relative to arthroscopy in the knee.

Materials and Methods:

Synthetic noise was added to images from clinical MRI scans (three‐dimensional SPACE pulse sequence; Siemens) from five patients who had undergone knee MRI with arthroscopic follow‐up, resulting in 25 simulated sets of images with standardized signal‐to‐noise ratios (SNRs) of 1, 2, 5, 10, or 20. All cases were scored by four musculoskeletal radiologists progressing from low to high SNR and grading all cartilage surfaces, major ligaments and menisci on a 5‐point scale. Receiver operator characteristic (ROC) curves were constructed for the detection of meniscal tears and cartilage abnormalities. The area under the ROC curve (AUC) was determined for each structure at each SNR level. In addition, reader confidence was measured and pairwise comparisons across SNR levels were performed. Results were compared with arthroscopy as the reference standard.

Results:

ROC AUC was maximized for meniscal tears at SNR = 5 (structure specific CNR = 3.2) and for cartilage abnormalities at SNR = 10 (CNR = 4.2). Observer confidence was maximized for menisci at SNR = 5 (CNR = 8.0), for ligaments at SNR = 10 (CNR = 13.6) and cartilage at SNR = 10 (CNR = 8.2).

Conclusion:

For 3D isotropic imaging in the knee, images with SNR < 10 or CNR < 10 should be rejected as nondiagnostic. J. Magn. Reson. Imaging 2013;37:1402–1408. © 2012 Wiley Periodicals, Inc.