Muskuloskeletal MR imaging at 3.0 T: current status and future perspectives

Quantitative and Comparative Analysis of Effectivity and Robustness for Enhanced and Optimized Non-Local Mean Filter Combining Pixel and Patch Information on MR Images of Musculoskeletal System

In the area of musculoskeletal MR images analysis, the image denoising plays an important role in enhancing the spatial image area for further processing. Recent studies have shown that non-local means (NLM) methods appear to be more effective and robust when compared with conventional local statistical filters, including median or average filters, when Rician noise is presented. A significant limitation of NLM is the fact that thy have the tendency to suppress tiny objects, which may represent clinically important information. For this reason, we provide an extensive quantitative and objective analysis of a novel NLM algorithm, taking advantage of pixel and patch similarity information with the optimization procedure for optimal filter parameters selection to demonstrate a higher robustness and effectivity, when comparing with NLM and conventional local means methods, including average and median filters. We provide extensive testing on variable noise generators with dynamical noise intensity to objectively demonstrate the robustness of the method in a noisy environment, which simulates relevant, variable and real conditions. This work also objectively evaluates the potential and benefits of the application of NLM filters in contrast to conventional local-mean filters. The final part of the analysis is focused on the segmentation performance when an NLM filter is applied. This analysis demonstrates a better performance of tissue identification with the application of smoothing procedure under worsening image conditions.

Validation of Peripheral Quantitative Computed Tomography-Derived Thigh Adipose Tissue Subcompartments in Young Girls Using a 3 T MRI Scanner

The ability to assess skeletal muscle adipose tissue is important given the negative clinical implications associated with greater fat infiltration of the muscle. Computed tomography and magnetic resonance imaging (MRI) are highly accurate for measuring appendicular soft tissue and muscle composition, but have limitations. Peripheral quantitative computed tomography (pQCT) is an alternative that investigators find valuable because of its low radiation, fast scan time, and comparatively lower costs. The present investigation sought to assess the accuracy of pQCT-derived estimates of total, subcutaneous, skeletal muscle, intermuscular, and calculated intramuscular adipose tissue areas, and muscle density in the midthigh of young girls using the gold standard, 3 T MRI, as the criterion. Cross-sectional data were analyzed for 26 healthy girls aged 9-12 years. Midthigh soft tissue composition was assessed by both pQCT and 3 T MRI. Mean tissue area for corresponding adipose compartments by pQCT and MRI was compared using t tests, regression analysis, and Bland-Altman plots. Muscle density was regressed on MRI skeletal muscle adipose tissue, intermuscular adipose tissue, and intramuscular adipose tissue, each expressed as a percentage of total muscle area. Correlations were high between MRI and pQCT for total adipose tissue (r² = 0.98), subcutaneous adipose tissue (r² = 0.95), skeletal muscle adipose tissue (r² = 0.83), and intermuscular adipose tissue (r² = 0.82), and pQCT muscle density correlated well with both MRI skeletal muscle adipose tissue (r² = 0.70) and MRI intermuscular adipose tissue (r² = 0.70). There was a slight, but statistically significant underestimation by pQCT for total and subcutaneous adipose tissue, whereas no significant difference was observed for skeletal muscle adipose tissue. Both pQCT-estimated intramuscular adipose tissue and muscle density were weakly correlated with MRI-intramuscular adipose tissue. We conclude that pQCT is a valid measurement technique for estimating all adipose subcompartments, except for intramuscular adipose tissue, for the midthigh region in young/adolescent girls.

Magnetic resonance imaging of the knee: An overview and update of conventional and state of the art imaging

Magnetic resonance imaging (MRI) has become the preferred modality for imaging the knee to show pathology and guide patient management and treatment. The knee is one of the most frequently injured joints, and knee pain is a pervasive difficulty that can affect all age groups. Due to the diverse pathology, complex anatomy, and a myriad of injury mechanisms of the knee, the MRI knee protocol and sequences should ensure detection of both soft tissue and osseous structures in detail and with accuracy. The knowledge of knee anatomy and the normal or injured MRI appearance of these key structures are critical for precise diagnosis. Advances in MRI technology provide the imaging necessary to obtain high-resolution images to evaluate menisci, ligaments, and tendons. Furthermore, recent advances in MRI techniques allow for improved imaging in the postoperative knee and metal artifact reduction, tumor imaging, cartilage evaluation, and visualization of nerves. As treatment and operative management techniques evolve, understanding the correct application of these advancements in MRI of the knee will prove to be valuable to clinical practice.

LEVEL OF EVIDENCE

5 J. MAGN. RESON. IMAGING 2017;45:1257-1275.

Standardized quantitative measurements of wrist cartilage in healthy humans using 3T magnetic resonance imaging

AIM: To quantify the wrist cartilage cross-sectional area in humans from a 3D magnetic resonance imaging (MRI) dataset and to assess the corresponding reproducibility.

METHODS: The study was conducted in 14 healthy volunteers (6 females and 8 males) between 30 and 58 years old and devoid of articular pain. Subjects were asked to lie down in the supine position with the right hand positioned above the pelvic region on top of a home-built rigid platform attached to the scanner bed. The wrist was wrapped with a flexible surface coil. MRI investigations were performed at 3T (Verio-Siemens) using volume interpolated breath hold examination (VIBE) and dual echo steady state (DESS) MRI sequences. Cartilage cross sectional area (CSA) was measured on a slice of interest selected from a 3D dataset of the entire carpus and metacarpal-phalangeal areas on the basis of anatomical criteria using conventional image processing radiology software. Cartilage cross-sectional areas between opposite bones in the carpal region were manually selected and quantified using a thresholding method.

RESULTS: Cartilage CSA measurements performed on a selected predefined slice were 292.4 ± 39 mm² using the VIBE sequence and slightly lower, 270.4 ± 50.6 mm², with the DESS sequence. The inter (14.1%) and intra (2.4%) subject variability was similar for both MRI methods. The coefficients of variation computed for the repeated measurements were also comparable for the VIBE (2.4%) and the DESS (4.8%) sequences. The carpus length averaged over the group was 37.5 ± 2.8 mm with a 7.45% between-subjects coefficient of variation. Of note, wrist cartilage CSA measured with either the VIBE or the DESS sequences was linearly related to the carpal bone length. The variability between subjects was significantly reduced to 8.4% when the CSA was normalized with respect to the carpal bone length.

CONCLUSION: The ratio between wrist cartilage CSA and carpal bone length is a highly reproducible standardized measurement which normalizes the natural diversity between individuals.

[Weightings and sequences in magnetic resonance imaging in orthopedic surgery]

Magnetic resonance imaging (MRI) plays a very important role in the diagnosis of musculoskeletal conditions; its importance in orthopedic trauma continues to grow. To ensure optimal imaging and to be able to answer all clinically relevant questions, some prerequisites must be taken into account. Of uttermost importance is a functioning communication between surgeons and radiologists. To adapt the best sequences, the radiologist needs to know all suspected injuries and the mechanism of trauma. Second, the surgeon must have basic knowledge regarding this technology to optimally use all its possibilities. The aim of this article is to familiarize the reader with basic MRI in traumatology focusing on weightings and sequences.

Early metacarpal bone mineral density loss using digital x-ray radiogrammetry and 3-tesla wrist MRI in established rheumatoid arthritis: a longitudinal one-year observational study

Objectives. Early change in rheumatoid arthritis (RA) is characterised by periarticular osteopenia. We investigated the relationship of early metacarpal digital X-ray radiogrammetry bone mineral density (DXR-BMD) change rate (RC-BMD, mg/cm²/month) to longitudinal changes in hand and feet radiographic and wrist MRI scores over 1 year. Materials and Methods. 10 RA patients completed the study and had wrist 3T-MRI and hand and feet X-rays at various time points over 1 year. MRI was scored by RAMRIS, X-ray was done by van der Heijde modified Sharp scoring, and RC-BMD was analysed using dxr-online. Results. There was good correlation amongst the two scorers for MRI measures and ICC for erosions: 0.984, BME: 0.943, and synovitis: 0.657. Strong relationships were observed between RC-BMD at 12-week and 1-year change in wrist marrow oedema (BME) (r = 0.78, P = 0.035) but not with erosion, synovitis, or radiographic scores. Conclusion. Early RC-BMD correlates with 1-year wrist BME change, which is a known predictor of future erosion and joint damage. However, in our pilot study, early RC-BMD did not show relationships to MRI erosion or radiographic changes over 1 year. This may reflect a slower kinetic in the appearance of MRI/radiographic erosions, generating the hypothesis that RC-BMD may be a more sensitive and early structural prognostic marker in RA follow-up.

Three-Tesla MR imaging of the elbow in non-symptomatic professional baseball pitchers

OBJECTIVES

To retrospectively evaluate the qualitative and quantitative 3-T MR imaging features of the elbow in non-symptomatic professional baseball pitchers presenting as major league draft picks or trades.

MATERIALS AND METHODS

The Institutional Review Board (IRB) approved the HIPPA-compliant study. Informed consent was waived. Twenty-one professional non-symptomatic baseball pitchers (mean age 23, range 18 to 34 years old) underwent 3-T MR imaging of the pitching elbow. Two experienced readers independently performed qualitative (collateral ligaments, tendons, cartilage, bones, ulnar nerve, olecranon fossa, and joint fluid) and quantitative (collateral ligaments and posteromedial plica) evaluation. Descriptive statistics were calculated.

RESULTS

Collateral ligament thickening was seen in a high proportion, nearly half, however, without features of full thickness tearing. Tendinosis without tearing was seen in 19 % (4/21) of common extensors. Cartilage abnormalities were infrequent. Bone abnormalities manifested as edema in 24 % (5/21) and humeroulnar osteophytosis. Ulnar nerve signal and/or morphologic abnormalities were seen in a very high proportion, up to 81 % (17/21). The olceranon fat pad showed scarring features in about one third. The median ligament thicknesses in mm measured: 4.6 UCL anterior bundle, 1.8 UCL posterior bundle, 1.9 RCL, 2.5 LUCL, and 0.7 mm anular. The median plica dimensions were 5.3 by 2.2 by 2.7 mm.

CONCLUSION

High-resolution 3-T MR imaging frequently shows abnormalities involving the ligaments, tendons, nerves, olecranon fat pad, and bones in non-symptomatic baseball pitchers.

Hip imaging of avascular necrosis at 7 Tesla compared with 3 Tesla

OBJECTIVES

To compare ultra-high field, high-resolution bilateral magnetic resonance imaging (MRI) of the hips at 7 Tesla (T) with 3 T MRI in patients with avascular necrosis (AVN) of the femoral head by subjective image evaluations, contrast measurements, and evaluation of the appearance of imaging abnormalities.

MATERIALS AND METHODS

Thirteen subjects with avascular necrosis treated using advanced core decompression underwent MRI at both 7 T and 3 T. Sequence parameters as well as resolution were kept identical for both field strengths. All MR images (MEDIC, DESS, PD/T2w TSE, T1w TSE, and STIR) were evaluated by two radiologists with regard to subjective image quality, soft tissue contrasts, B1 homogeneity (four-point scale, higher values indicating better image quality) and depiction of imaging abnormalities of the femoral heads (three-point scale, higher values indicating the superiority of 7 T). Contrast ratios of soft tissues were calculated and compared with subjective data.

RESULTS

7-T imaging of the femoral joints, as well as 3-T imaging, achieved "good" to "very good" quality in all sequences. 7 T showed significantly higher soft tissue contrasts for T2w and MEDIC compared with 3 T (cartilage/fluid: 2.9 vs 2.2 and 3.6 vs 2.6), better detailed resolution for cartilage defects (PDw, T2w, T1w, MEDIC, DESS > 2.5) and better visibility of joint effusions (MEDIC 2.6; PDw/T2w 2.4; DESS 2.2). Image homogeneity compared with 3 T (3.9-4.0 for all sequences) was degraded, especially in TSE sequences at 7 T through signal variations (7 T: 2.1-2.9); to a lesser extent also GRE sequences (7 T: 2.9-3.5). Imaging findings related to untreated or treated AVN were better delineated at 3 T (≤1.8), while joint effusions (2.2-2.6) and cartilage defects (2.5-3.0) were better visualized at 7 T. STIR performed much more poorly at 7 T, generating large contrast variations (1.5).

CONCLUSIONS

7-T hip MRI showed comparable results in hip joint imaging compared with 3 T with slight advantages in contrast detail (cartilage defects) and fluid detection at 7 T when accepting image degradation medially.

Evaluation of the WARP-turbo spin echo sequence for 3 Tesla magnetic resonance imaging of stifle joints in dogs with stainless steel tibial plateau leveling osteotomy implants

Susceptibility artifacts caused by ferromagnetic implants compromise magnetic resonance imaging (MRI) of the canine stifle after tibial plateau leveling osteotomy (TPLO) procedures. The WARP-turbo spin echo sequence is being developed to mitigate artifacts and utilizes slice encoding for metal artifact reduction. The aim of the current study was to evaluate the WARP-turbo spin echo sequence for imaging post TPLO canine stifle joints. Proton density weighted images of 19 canine cadaver limbs were made post TPLO using a 3 Tesla MRI scanner. Susceptibility artifact sizes were recorded and compared for WARP vs. conventional turbo spin echo sequences. Three evaluators graded depiction quality for the tibial tuberosity, medial and lateral menisci, tibial osteotomy, and caudal cruciate ligament as sufficient or insufficient to make a diagnosis. Artifacts were subjectively smaller and local structures were better depicted in WARP-turbo spin echo images. Signal void area was also reduced by 75% (sagittal) and 49% (dorsal) in WARP vs. conventional turbo spin echo images. Evaluators were significantly more likely to grade local anatomy depiction as adequate for making a diagnosis in WARP-turbo spin echo images in the sagittal but not dorsal plane. The proportion of image sets with anatomic structure depiction graded adequate to make a diagnosis ranged from 28 to 68% in sagittal WARP-turbo spin echo images compared to 0-19% in turbo spin echo images. Findings indicated that the WARP-turbo spin echo sequence reduces the severity of susceptibility artifacts in canine stifle joints post TPLO. However, variable depiction of local anatomy warrants further refinement of the technique.

Bilateral hip imaging at 7 Tesla using a multi-channel transmit technology: initial results presenting anatomical detail in healthy volunteers and pathological changes in patients with avascular necrosis of the femoral head

OBJECTIVE

To evaluate 7-T MRI of both hips using a multi-channel transmit technology to compensate for inherent B1 inhomogeneities in volunteers and patients with avascular necrosis of the femoral head.

MATERIALS AND METHODS

A self-built, eight-channel transmit-receive coil was utilized for B1 modification at 7 T. Two shim modes (individual shim vs. CP2+ mode) were initially compared and the best shim result was used for all further imaging. Robustness of sequences against B1 inhomogeneities, appearance of anatomic and pathologic changes of the femoral heads of MEDIC, DESS, PD/T2w TSE, T1w TSE, and STIR sequences at 7 T were evaluated in 12 subjects on a four-point scale (1-4): four male volunteers and eight patients (seven males, one female) suffering from avascular necrosis treated by advanced core decompression.

RESULTS

Successful MRI of both femoral heads was achieved in all 12 subjects. CP2+ mode proved superior in ten of 12 cases. DESS proved most robust against B1 inhomogeneity. Anatomical details (labrum, articular cartilage) were best depicted in PDw, MEDIC, and DESS, while for depiction of pathological changes PDw, DESS (0.76 mm(3)) and T1w were superior.

CONCLUSIONS

Our initial results of ultra-high-field hip joint imaging demonstrate high-resolution, high-contrast images with a good depiction of anatomic and pathologic changes. However, shifting areas of signal dropout from the femoral heads to the center of the pelvis makes these areas not assessable. For clinical workflow CP2+ mode is most practical. Seven-Tesla MRI of the hip joints may become a valuable complement to clinical field strengths.

Evaluating automated dynamic contrast enhanced wrist 3T MRI in healthy volunteers: one-year longitudinal observational study

RATIONAL AND OBJECTIVE

Dynamic contrast enhanced (DCE)-MRI has great potential to provide quantitative measure of inflammatory activity in rheumatoid arthritis. There is no current benchmark to establish the stability of signal in the joints of healthy subjects when imaged with DCE-MRI longitudinally, which is crucial so as to differentiate changes induced by treatment from the inherent variability of perfusion measures. The objective of this study was to test a pixel-by-pixel parametric map based approach for analysis of DCE-MRI (Dynamika) and to investigate the variability in signal characteristics over time in healthy controls using longitudinally acquired images.

MATERIALS AND METHODS

10 healthy volunteers enrolled, dominant wrists were imaged with contrast enhanced 3T MRI at baseline, week 12, 24 and 52 and scored with RAMRIS, DCE-MRI was analysed using a novel quantification parametric map based approach. Radiographs were obtained at baseline and week 52 and scored using modified Sharp van der Heidje method. RAMRIS scores and dynamic MRI measures were correlated.

RESULTS

No erosions were seen on radiographs, whereas MRI showed erosion-like changes, low grade bone marrow oedema and low-moderate synovial enhancement. The DCE-MRI parameters were stable (baseline scores, variability) (mean±st.dev); in whole wrist analysis, MEmean (1.3±0.07, -0.08±0.1 at week 24) and IREmean (0.008±0.004, -0.002±0.005 at week 12 and 24). In the rough wrist ROI, MEmean (1.2±0.07, 0.04±0.02 at week 52) and IREmean (0.001±0.0008, 0.0006±0.0009 at week 52) and precise wrist ROI, MEmean (1.2±0.09, 0.04±0.04 at week 52) and IREmean (0.001±0.0008, 0.0008±0.001 at week 24 and 52). The Dynamic parameters obtained using fully automated analysis demonstrated strong, statistically significant correlations with RAMRIS synovitis scores.

CONCLUSION

The study demonstrated that contrast enhancement does occur in healthy volunteers but the inherent variability of perfusion measures obtained with quantitative DCE-MRI method is low and stable, suggesting its suitability for longitudinal studies of inflammatory arthritis. These results also provide important information regarding potential cut-off levels for imaging remission goals in patients with RA using both RAMRIS and DCE-MRI extracted parametric parameters.

Knee derangements: comparison of isotropic 3D fast spin-echo, isotropic 3D balanced fast field-echo, and conventional 2D fast spin-echo MR imaging

PURPOSE

To compare diagnostic performance, subjective image quality, and artifacts of isotropic three-dimensional (3D) intermediate-weighted (IW) fast spin-echo (SE), isotropic 3D balanced fast field-echo (FFE), and conventional two-dimensional (2D) fast SE 3.0-T MR sequences in evaluation of cartilage, ligaments, menisci, and osseous knee structures in symptomatic patients.

MATERIALS AND METHODS

Institutional review board approval and waiver of informed consent were obtained for this HIPAA-compliant study. One hundred MR studies, each with three data sets (3D IW fast SE, 3D balanced FFE, 2D fast SE), were reviewed retrospectively. Two radiologists independently evaluated images for cartilaginous defects, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial meniscus (MM), lateral meniscus (LM) tears, subchondral bone marrow signal abnormalities, subjective image quality, and image artifacts. Arthroscopic results were the reference standard. Statistical analysis was performed to calculate interobserver agreement and compare diagnostic performance of sequences.

RESULTS

Sensitivity and specificity were greater than 85% for all lesions. For cartilaginous defects, sensitivity of 3D IW fast SE was significantly greater than that of 3D balanced FFE (95.5% vs 89.7%). Sensitivity of 3D IW fast SE and 2D fast SE for MM, LM, and ACL tears tended to be greater than that of 3D balanced FFE. IW fast SE had a higher detection rate for subchondral bone marrow signal abnormality than did 3D balanced FFE (34% vs 21%); it also had the best image quality and fewest artifacts, followed by 2D fast SE and 3D balanced FFE. Interobserver agreement was excellent for evaluation of all intraarticular structures (κ = 0.85-1) and good to excellent for detection of subchondral bone marrow signal abnormality (κ = 0.76-0.91).

CONCLUSION

The performance of IW fast SE is superior to that of balanced FFE in evaluation of cartilaginous defects, with no significant difference in performance between 2D fast SE, 3D IW fast SE, and 3D balanced FFE in evaluation of meniscal and ligament tears. Subchondral bone marrow signal abnormality is more easily seen on 3D IW fast SE images, with better subjective image quality and fewer artifacts, than on images obtained with other techniques.

In vivo visualization of the levator ani muscle subdivisions using MR fiber tractography with diffusion tensor imaging

Understanding the levator ani complex architecture is of major clinical relevance. The aim of this study was to determine the feasibility of magnetic resonance (MR) fiber tractography with diffusion tensor imaging (DTI) as a tool for the three-dimensional (3D) representation of normal subdivisions of the levator ani. Ten young nulliparous female volunteers underwent DTI at 1.5 T MR imaging. Diffusion-weighted axial sequence of the pelvic floor was performed with additional T2-weighted multiplanar sequences for anatomical reference. Fiber tractography for visualization of each Terminologia Anatomica-listed major levator ani subdivision was performed. Numeric muscular fibers extracted after tractography were judged as accurate when localized within the boundaries of the muscle, and inaccurate when projecting out of the boundaries of the muscle. From the fiber tracking of each subdivision the number of numeric fibers (inaccurate and accurate) and a score (from 3 to 0) of the adequacy of the 3D representation were calculated. All but two volunteers completed the protocol. The mean number of accurate fibers was 17 ± 2 for the pubovisceralis, 14 ± 6 for the puborectalis and 1 ± 1 for the iliococcygeus. The quality of the 3D representation was judged as good (score = 2) for the pubovisceralis and puborectalis, and inaccurate (score = 0) for the iliococcygeus. Our study is the first step to a 3D visualization of the three major levator ani subdivisions, which could help to better understand their in vivo functional anatomy.

Advances in pediatric body MRI

MRI offers an alternative to CT, and thus is central to an ALARA strategy. However, long exam times, limited magnet availability, and motion artifacts are barriers to expanded use of MRI. This article reviews developments in pediatric body MRI that might reduce these barriers: high field systems, acceleration, navigation and newer contrast agents.

Advanced morphological 3D magnetic resonance observation of cartilage repair tissue (MOCART) scoring using a new isotropic 3D proton-density, turbo spin echo sequence with variable flip angle distribution (PD-SPACE) compared to an isotropic 3D steady-state free precession sequence (True-FISP) and standard 2D sequences

PURPOSE

To evaluate a new isotropic 3D proton-density, turbo-spin-echo sequence with variable flip-angle distribution (PD-SPACE) sequence compared to an isotropic 3D true-fast-imaging with steady-state-precession (True-FISP) sequence and 2D standard MR sequences with regard to the new 3D magnetic resonance observation of cartilage repair tissue (MOCART) score.

MATERIALS AND METHODS

Sixty consecutive MR scans on 37 patients (age: 32.8 ± 7.9 years) after matrix-associated autologous chondrocyte transplantation (MACT) of the knee were prospectively included. The 3D MOCART score was assessed using the standard 2D sequences and the multiplanar-reconstruction (MPR) of both isotropic sequences. Statistical, Bonferroni-corrected correlation as well as subjective quality analysis were performed.

RESULTS

The correlation of the different sequences was significant for the variables defect fill, cartilage interface, bone interface, surface, subchondral lamina, chondral osteophytes, and effusion (Pearson coefficients 0.514-0.865). Especially between the standard sequences and the 3D True-FISP sequence, the variables structure, signal intensity, subchondral bone, and bone marrow edema revealed lower, not significant, correlation values (0.242-0.383). Subjective quality was good for all sequences (P ≥ 0.05). Artifacts were most often visible on the 3D True-FISP sequence (P < 0.05).

CONCLUSION

Different isotropic sequences can be used for the 3D evaluation of cartilage repair with the benefits of isotropic 3D MRI, MPR, and a significantly reduced scan time, where the 3D PD-SPACE sequence reveals the best results.

An eight-channel transmit/receive multipurpose coil for musculoskeletal MR imaging at 7 T

PURPOSE

MRI plays a leading diagnostic role in assessing the musculoskeletal (MSK) system and is well established for most questions at clinically used field strengths (up to 3 T). However, there are still limitations in imaging early stages of cartilage degeneration, very fine tendons and ligaments, or in locating nerve lesions, for example. 7 T MRI of the knee has already received increasing attention in the current published literature, but there is a strong need to develop new radiofrequency (RF) coils to assess more regions of the MSK system. In this work, an eight-channel transmit/receive RF array was built as a multipurpose coil for imaging some of the thus far neglected regions. An extensive coil characterization protocol and first in vivo results of the human wrist, shoulder, elbow, knee, and ankle imaged at 7 T will be presented.

METHODS

Eight surface loop coils with a dimension of 6 x 7 cm2 were machined from FR4 circuit board material. To facilitate easy positioning, two coil clusters, each with four loop elements, were combined to one RF transmit/receive array. An overlapped and shifted arrangement of the coil elements was chosen to reduce the mutual inductance between neighboring coils. A phantom made of body-simulating liquid was used for tuning and matching on the bench. Afterward, the S-parameters were verified on a human wrist, elbow, and shoulder. For safety validation, a detailed compliance test was performed including full wave simulations of the RF field distribution and the corresponding specific absorption rate (SAR) for all joints. In vivo images of four volunteers were assessed with gradient echo and spin echo sequences modified to obtain optimal image contrast, full anatomic coverage, and the highest spatial resolution within a reasonable acquisition time. The performance of the RF coil was additionally evaluated by in vivo B1 mapping.

RESULTS

A comparison of B1 per unit power, flip angle distribution, and anatomic images showed a fairly homogeneous excitation for the smaller joints (elbow, wrist, and ankle), while for the larger joints, the shoulder and especially the knee, B1 inhomogeneities and limited penetration depth were more pronounced. However, the greater part of the shoulder joint could be imaged. In vivo images rendered very fine anatomic details such as fascicles of the median nerve and the branching of the nerve bundles. High-resolution images of cartilage, labrum, and tendons could be acquired. Additionally, turbo spin echo (TSE) and inversion recovery sequences performed very well.

CONCLUSIONS

This study demonstrates that the concept of two four-channel transmit/receive RF arrays can be used as a multipurpose coil for high-resolution in vivo MR imaging of the musculoskeletal system at 7 T. Not only gradient echo but also typical clinical and SAR-intensive sequences such as STIR and TSE performed well. Imaging of small structures and peripheral nerves could in particular benefit from this technique.

State-of-the-art in pediatric body and musculoskeletal magnetic resonance imaging

Pediatric body and musculoskeletal MRI has seen tremendous advances over the past few years. These advances have enabled high-quality imaging in even the smallest children and expanded the range of clinical problems amenable to MRI. In this review, we highlight some advances: transition to 3 Tesla, parallel imaging, motion compensation, and new contrast agents. Given the increasing saliency of concerns regarding ionizing radiation from computed tomography, these advances could not be more welcome.

Imaging of soft tissues adjacent to orthopedic hardware: comparison of 3-T and 1.5-T MRI

OBJECTIVE

The purpose of this study was to compare metal artifact reduction techniques at 1.5-T and 3-T MRI.

MATERIALS AND METHODS

A titanium plate with steel screws was placed in a freshly harvested pig leg. The leg was imaged with 1.5-T and 3-T MRI. A T2-weighted turbo spin-echo sequence was used with echo-train lengths of 8, 16, 32, and 64 and a constant readout bandwidth of 31.2 kHz. The images were compared qualitatively, and the optimal echo-train length was selected. Images were acquired at the optimal echo-train length with four different readout bandwidths. Artifact was measured quantitatively, and image quality was ranked qualitatively. The qualitatively best image acquired at 1.5 T was compared with the qualitatively highest-ranked image acquired at 3 T.

RESULTS

At both 1.5 T and 3 T, optimal images of equal quality were produced at echo-train lengths of 8 and 16. At higher readout bandwidths, there was quantitatively less artifact. The qualitatively best images were acquired at a readout bandwidth of 31.2 kHz at 1.5 T and 62.5 kHz at 3 T (Cronbach's alpha=1.00). The optimal image at 3 T was qualitatively superior to that at 1.5 T.

CONCLUSION

Optimizing image acquisition parameters in this phantom model resulted in similar quantitative susceptibility artifact at 3 T and 1.5 T and better qualitative images at 3 T than at 1.5 T.

Three-dimensional magnetic resonance observation of cartilage repair tissue (MOCART) score assessed with an isotropic three-dimensional true fast imaging with steady-state precession sequence at 3.0 Tesla

INTRODUCTION

Cartilage defects are common pathologies and surgical cartilage repair shows promising results. In its postoperative evaluation, the magnetic resonance observation of cartilage repair tissue (MOCART) score, using different variables to describe the constitution of the cartilage repair tissue and the surrounding structures, is widely used. High-field magnetic resonance imaging (MRI) and 3-dimensional (3D) isotropic sequences may combine ideal preconditions to enhance the diagnostic performance of cartilage imaging.Aim of this study was to introduce an improved 3D MOCART score using the possibilities of an isotropic 3D true fast imaging with steady-state precession (True-FISP) sequence in the postoperative evaluation of patients after matrix-associated autologous chondrocyte transplantation (MACT) as well as to compare the results to the conventional 2D MOCART score using standard MR sequences.

MATERIAL AND METHODS

The study had approval by the local ethics commission. One hundred consecutive MR scans in 60 patients at standard follow-up intervals of 1, 3, 6, 12, 24, and 60 months after MACT of the knee joint were prospectively included. The mean follow-up interval of this cross-sectional evaluation was 21.4 +/- 20.6 months; the mean age of the patients was 35.8 +/- 9.4 years. MRI was performed at a 3.0 Tesla unit. All variables of the standard 2D MOCART score where part of the new 3D MOCART score. Furthermore, additional variables and options were included with the aims to use the capabilities of isotropic MRI, to include the results of recent studies, and to adapt to the needs of patients and physician in a clinical routine examination. A proton-density turbo spin-echo sequence, a T2-weighted dual fast spin-echo (dual-FSE) sequence, and a T1-weighted turbo inversion recovery magnitude (TIRM) sequence were used to assess the standard 2D MOCART score; an isotropic 3D-TrueFISP sequence was prepared to evaluate the new 3D MOCART score. All 9 variables of the 2D MOCART score were compared with the corresponding variables obtained by the 3D MOCART score using the Pearson correlation coefficient; additionally the subjective quality and possible artifacts of the MR sequences were analyzed.

RESULTS

The correlation between the standard 2D MOCART score and the new 3D MOCART showed for the 8 variables "defect fill," "cartilage interface," "surface," "adhesions," "structure," "signal intensity," "subchondral lamina," and "effusion"-a highly significant (P < 0.001) correlation with a Pearson coefficient between 0.566 and 0.932. The variable "bone marrow edema" correlated significantly (P < 0.05; Pearson coefficient: 0.257). The subjective quality of the 3 standard MR sequences was comparable to the isotropic 3D-TrueFISP sequence. Artifacts were more frequently visible within the 3D-TrueFISP sequence.

CONCLUSION

In the clinical routine follow-up after cartilage repair, the 3D MOCART score, assessed by only 1 high-resolution isotropic MR sequence, provides comparable information than the standard 2D MOCART score. Hence, the new 3D MOCART score has the potential to combine the information of the standard 2D MOCART score with the possible advantages of isotropic 3D MRI at high-field. A clear limitation of the 3D-TrueFISP sequence was the high number of artifacts. Future studies have to prove the clinical benefits of a 3D MOCART score.

Initial results of in vivo high-resolution morphological and biochemical cartilage imaging of patients after matrix-associated autologous chondrocyte transplantation (MACT) of the ankle

OBJECTIVE

The aim of this study was to use morphological as well as biochemical (T2 and T2* relaxation times and diffusion-weighted imaging (DWI)) magnetic resonance imaging (MRI) for the evaluation of healthy cartilage and cartilage repair tissue after matrix-associated autologous chondrocyte transplantation (MACT) of the ankle joint.

MATERIALS AND METHODS

Ten healthy volunteers (mean age, 32.4 years) and 12 patients who underwent MACT of the ankle joint (mean age, 32.8 years) were included. In order to evaluate possible maturation effects, patients were separated into short-term (6-13 months) and long-term (20-54 months) follow-up cohorts. MRI was performed on a 3.0-T magnetic resonance (MR) scanner using a new dedicated eight-channel foot-and-ankle coil. Using high-resolution morphological MRI, the magnetic resonance observation of cartilage repair tissue (MOCART) score was assessed. For biochemical MRI, T2 mapping, T2* mapping, and DWI were obtained. Region-of-interest analysis was performed within native cartilage of the volunteers and control cartilage as well as cartilage repair tissue in the patients subsequent to MACT.

RESULTS

The overall MOCART score in patients after MACT was 73.8. T2 relaxation times (approximately 50 ms), T2* relaxation times (approximately 16 ms), and the diffusion constant for DWI (approximately 1.3) were comparable for the healthy volunteers and the control cartilage in the patients after MACT. The cartilage repair tissue showed no significant difference in T2 and T2* relaxation times (p > or = 0.05) compared to the control cartilage; however, a significantly higher diffusivity (approximately 1.5; p < 0.05) was noted in the cartilage repair tissue.

CONCLUSION

The obtained results suggest that besides morphological MRI and biochemical MR techniques, such as T2 and T2* mapping, DWI may also deliver additional information about the ultrastructure of cartilage and cartilage repair tissue in the ankle joint using high-field MRI, a dedicated multichannel coil, and sophisticated sequences.

In vivo biochemical 7.0 Tesla magnetic resonance: preliminary results of dGEMRIC, zonal T2, and T2* mapping of articular cartilage

INTRODUCTION

Ultra-high-field whole-body systems (7.0 T) have a high potential for future human in vivo magnetic resonance imaging (MRI). In musculoskeletal MRI, biochemical imaging of articular cartilage may benefit, in particular. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) and T2 mapping have shown potential at 3.0 T. Although dGEMRIC, allows the determination of the glycosaminoglycan content of articular cartilage, T2 mapping is a promising tool for the evaluation of water and collagen content. In addition, the evaluation of zonal variation, based on tissue anisotropy, provides an indicator of the nature of cartilage ie, hyaline or hyaline-like articular cartilage.Thus, the aim of our study was to show the feasibility of in vivo dGEMRIC, and T2 and T2* relaxation measurements, at 7.0 T MRI; and to evaluate the potential of T2 and T2* measurements in an initial patient study after matrix-associated autologous chondrocyte transplantation (MACT) in the knee.

MATERIALS AND METHODS

MRI was performed on a whole-body 7.0 T MR scanner using a dedicated circular polarization knee coil. The protocol consisted of an inversion recovery sequence for dGEMRIC, a multiecho spin-echo sequence for standard T2 mapping, a gradient-echo sequence for T2* mapping and a morphologic PD SPACE sequence. Twelve healthy volunteers (mean age, 26.7 +/- 3.4 years) and 4 patients (mean age, 38.0 +/- 14.0 years) were enrolled 29.5 +/- 15.1 months after MACT. For dGEMRIC, 5 healthy volunteers (mean age, 32.4 +/- 11.2 years) were included. T1 maps were calculated using a nonlinear, 2-parameter, least squares fit analysis. Using a region-of-interest analysis, mean cartilage relaxation rate was determined as T1 (0) for precontrast measurements and T1 (Gd) for postcontrast gadopentate dimeglumine [Gd-DTPA(2-)] measurements. T2 and T2* maps were obtained using a pixelwise, monoexponential, non-negative least squares fit analysis; region-of-interest analysis was carried out for deep and superficial cartilage aspects. Statistical evaluation was performed by analyses of variance.

RESULTS

Mean T1 (dGEMRIC) values for healthy volunteers showed slightly different results for femoral [T1 (0): 1259 +/- 277 ms; T1 (Gd): 683 +/- 141 ms] compared with tibial cartilage [T1 (0): 1093 +/- 281 ms; T1 (Gd): 769 +/- 150 ms]. Global mean T2 relaxation for healthy volunteers showed comparable results for femoral (T2: 56.3 +/- 15.2 ms; T2*: 19.7 +/- 6.4 ms) and patellar (T2: 54.6 +/- 13.0 ms; T2*: 19.6 +/- 5.2 ms) cartilage, but lower values for tibial cartilage (T2: 43.6 +/- 8.5 ms; T2*: 16.6 +/- 5.6 ms). All healthy cartilage sites showed a significant increase from deep to superficial cartilage (P < 0.001). Within healthy cartilage sites in MACT patients, adequate values could be found for T2 (56.6 +/- 13.2 ms) and T2* (18.6 +/- 5.3 ms), which also showed a significant stratification. Within cartilage repair tissue, global mean values showed no difference, with 55.9 +/- 4.9 ms for T2 and 16.2 +/- 6.3 ms for T2*. However, zonal assessment showed only a slight and not significant increase from deep to superficial cartilage (T2: P = 0.174; T2*: P = 0.150).

CONCLUSION

In vivo T1 dGEMRIC assessment in healthy cartilage, and T2 and T2* mapping in healthy and reparative articular cartilage, seems to be possible at 7.0 T MRI. For T2 and T2*, zonal variation of articular cartilage could also be evaluated at 7.0 T. This zonal assessment of deep and superficial cartilage aspects shows promising results for the differentiation of healthy and affected articular cartilage. In future studies, optimized protocol selection, and sophisticated coil technology, together with increased signal at ultra-high-field MRI, may lead to advanced biochemical cartilage imaging.

Musculoskeletal MR imaging at 3 T

MR imaging plays a major role in the assessment of pediatric musculoskeletal disease. Compared with 1.5 T MR imaging, 3 T magnets provide images with an increased signal-to-noise ratio, which is particularly helpful when assessing small body parts and structures in children. This article discusses the advantages and challenges associated with musculoskeletal MR imaging at 3 T, basic scanning protocols, image optimization techniques, and specific clinical applications in a pediatric population.

Advances in pediatric MR imaging

This article describes the considerable technical achievements that have been made in MR imaging in the evaluation of pediatric patients. The latest techniques in improving signal intensity, resolution, and speed are discussed. The multitude of new options for pediatric MR imaging are illustrated, including higher field strength imaging, multi-channel coil technology coupled with parallel imaging, and new pulse sequence designs. Several future directions in the field of pediatric body and musculoskeletal imaging also are highlighted.

Three Tesla MRI for the diagnosis of meniscal and anterior cruciate ligament pathology: a comparison to arthroscopic findings

AIM

To assess the accuracy of 3T magnetic resonance imaging (MRI) in the evaluation of meniscal and anterior cruciate ligament (ACL) injury.

MATERIALS AND METHODS

Sixty-one consecutive patients were identified who were referred for evaluation of suspected intra-articular pathology with a 3T MRI and who, subsequently, underwent an arthroscopic procedure of the knee were included for the study. Two musculoskeletal radiologists interpreted the images. The sensitivity, specificity, positive predictive value, and negative predictive value were then calculated for the MRI versus the arthroscopic findings as a reference standard.

RESULTS

The sensitivity and specificity for the overall detection of meniscal tears in this study was 84 and 93%, respectively. The results for the medial meniscus separately were 91 and 93% and for the lateral 77 and 93%. The evaluation of ACL integrity was 100% sensitive and specific. The meniscal tear type was correctly identified in 75% of cases and its location in 94%.

CONCLUSION

This study demonstrates good results of 3T MRI in the evaluation of the injured knee. Caution should still be given to the interpretation on MRI of a lateral meniscus tear, and it is suggested that the standard diagnostic criteria of high signal reaching the articular surface on two consecutive image sections be adhered to even at these higher field strengths.

High-resolution morphological and biochemical imaging of articular cartilage of the ankle joint at 3.0 T using a new dedicated phased array coil: in vivo reproducibility study

OBJECTIVE

The objective of this study was to evaluate the feasibility and reproducibility of high-resolution magnetic resonance imaging (MRI) and quantitative T2 mapping of the talocrural cartilage within a clinically applicable scan time using a new dedicated ankle coil and high-field MRI.

MATERIALS AND METHODS

Ten healthy volunteers (mean age 32.4 years) underwent MRI of the ankle. As morphological sequences, proton density fat-suppressed turbo spin echo (PD-FS-TSE), as a reference, was compared with 3D true fast imaging with steady-state precession (TrueFISP). Furthermore, biochemical quantitative T2 imaging was prepared using a multi-echo spin-echo T2 approach. Data analysis was performed three times each by three different observers on sagittal slices, planned on the isotropic 3D-TrueFISP; as a morphological parameter, cartilage thickness was assessed and for T2 relaxation times, region-of-interest (ROI) evaluation was done. Reproducibility was determined as a coefficient of variation (CV) for each volunteer; averaged as root mean square (RMSA) given as a percentage; statistical evaluation was done using analysis of variance.

RESULTS

Cartilage thickness of the talocrural joint showed significantly higher values for the 3D-TrueFISP (ranging from 1.07 to 1.14 mm) compared with the PD-FS-TSE (ranging from 0.74 to 0.99 mm); however, both morphological sequences showed comparable good results with RMSA of 7.1 to 8.5%. Regarding quantitative T2 mapping, measurements showed T2 relaxation times of about 54 ms with an excellent reproducibility (RMSA) ranging from 3.2 to 4.7%.

CONCLUSION

In our study the assessment of cartilage thickness and T2 relaxation times could be performed with high reproducibility in a clinically realizable scan time, demonstrating new possibilities for further investigations into patient groups.

A review of MR physics: 3T versus 1.5T

This article illustrates changes in the underlying physics concepts related to increasing the main magnetic field from 1.5T to 3T. The effects of these changes on tissue constants and practical hardware limitations is discussed as they affect scan time, quality, and contrast. Changes in susceptibility artifacts, chemical shift artifacts, and dielectric effects as a result of the increased field strength are also illustrated. Based on these fundamental considerations, an overall understanding of the benefits and constraints of signal-to-noise ratio and contrast-to-noise ratio changes between 1.5T and 3T MR systems is developed.

Cardiac cine MRI: comparison of 1.5 T, non-enhanced 3.0 T and blood pool enhanced 3.0 T imaging

INTRODUCTION

Cardiac cine imaging using balanced steady state free precession sequences (bSSFP) suffers from artefacts at 3.0 T. We compared bSSFP cardiac cine imaging at 1.5 T with gradient echo imaging at 3.0 T with and without a blood pool contrast agent.

MATERIALS AND METHODS

Eleven patients referred for cardiac cine imaging underwent imaging at 1.5 T and 3.0 T. At 3.0 T images were acquired before and after administration of 0.03 mmol/kg gadofosveset. Blood pool signal-to-noise ratio (SNR), temporal variations in SNR, ejection fraction and myocardial mass were compared. Subjective image quality was scored on a four-point scale.

RESULTS

Blood pool SNR increased with more than 75% at 3.0 T compared to 1.5 T (p<0.001); after contrast administration at 3.0 T SNR increased with 139% (p<0.001). However, variations in blood pool SNR at 3.0 T were nearly three times as high versus those at 1.5 T in the absence of contrast medium (p<0.001); after contrast administration this was reduced to approximately a factor 1.4 (p=0.21). Saturation artefacts led to significant overestimation of ejection fraction in the absence of contrast administration (1.5 T: 44.7+/-3.1 vs. 3.0 T: 50.7+/-4.2 [p=0.04] vs. 3.0 T post contrast: 43.4+/-2.9 [p=0.55]). Subjective image quality was highest for 1.5 T (2.8+/-0.3), and lowest for non-enhanced 3.0 T (1.7+/-0.6; p=0.006).

CONCLUSIONS

GRE cardiac cine imaging at 3.0 T after injection of the blood pool agent gadofosveset leads to improved objective and subjective cardiac cine image quality at 3.0 T and to the same conclusions regarding cardiac ejection fraction compared to bSSFP imaging at 1.5 T.

MR imaging of the posterolateral corner of the knee

The posterolateral corner (PLC) is a complex functional unit, consisting of several structures, which is responsible for posterolateral stabilization. The PLC is not consistently defined in the literature. However, most descriptions include the popliteal tendon (PT), the lateral collateral ligament (LCL), the popliteofibular ligament (PFL) and the posterolateral capsule, which is reinforced by the arcuate ligament (AL) and the fabellofibular ligament (FFL). Knowledge of PLC anatomy, including its variations, and understanding of the biomechanics is important for correct diagnosis of PLC injuries. An overlooked PLC injury can result in chronic instability, chronic pain, and, eventually, in secondary osteoarthritis. Damage to the PLC also has an adverse effect on the outcome of cruciate ligament repair. Isolated lesions of the PLC are rare. PLC lesions are typically associated with injuries of the cruciate ligaments, the menisci, bone and soft tissue. In the acute phase, clinical findings can be difficult to interpret due to pain and swelling. Magnetic resonance (MR) imaging potentially demonstrates the entire spectrum of PLC injuries and associated lesions of the knee, including those that may be overlooked during clinical examination or arthroscopy.