Cartilage morphology at 3.0T: assessment of three-dimensional magnetic resonance imaging techniques

Radial Planes in Hip Magnetic Resonance Imaging: Techniques, Applications, and Perspectives

The hip cartilage and labrum, as the main targets of femoroacetabular impingement, sports-related or traumatic damage, as well as congenital and developmental abnormalities, have attracted increasing attention with the development of magnetic resonance imaging (MRI) and hip arthroscopy. MRI is a commonly used imaging modality to noninvasively visualize the hip cartilage and labral lesions. However, conventional orthogonal MRI planes encounter unique challenges given the ball-and-socket configuration of the hip joint, its anatomically abducted and anteverted orientation, and the thin, closely apposed cartilage enveloping the femoral head and acetabulum. Advancements in hip MRI's radial plane, which is acquired through the center of the hip joint, offer a solution. This technology provides true cross-sectional images of the cartilage and labrum perpendicular to the curvature of the joint, thereby mitigating the partial-volume-averaging effects. The integration of 3.0-Tesla high field strength and three-dimensional (3D) acquisition techniques further enhances the capabilities of the radial plane. This combination yields a high signal-to-noise ratio, high spatial resolution, high contrast between intraarticular structures, while minimizing partial-volume-averaging effects. Such improvements potentially facilitate the comprehensive detection of even minor chondral and labral lesions. The capability for multiplanar reconstruction from a single 3D volumetric acquisition further strengthens the usefulness of the radial plane by aiding in precise localization of hip cartilage and labral lesions, in line with hip arthroscopy findings. These advancements have the potential to standardize MRI evaluations and radiographic reporting systems for hip cartilage and labrum, offering precise guidance for hip arthroscopy. This article presents a comprehensive review of radial plane technology applied to the hip MRI, and discusses the morphological assessment and localization of hip cartilage and labral lesions utilizing this advanced imaging technique. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 2.

Preoperative and Postoperative Imaging and Outcome Scores for Osteochondral Lesion Repair of the Ankle

Cartilage lesions to the ankle joint are common and can result in pain and functional limitations. Surgical treatment aims to restore the damaged cartilage's integrity and quality. However, the current evidence for establishing best practices in ankle cartilage repair is characterized by limited quality and a low level of evidence. One of the contributing factors is the lack of standardized preoperative and postoperative assessment methods to evaluate treatment effectiveness and visualize repaired cartilage. This review article seeks to examine the importance of preoperative imaging, classification systems, patient-reported outcome measures, and radiological evaluation techniques for cartilage repair surgeries.

Multi-echo in steady-state acquisition improves MRI image quality and lumbosacral radiculopathy diagnosis efficacy compared with T2 fast spin-echo sequence

PURPOSE

This study compares the performance of a 4-min multi-echo in steady-state acquisition (MENSA) with a 6-min fast spin echo with variable flip angle (CUBE) protocol for the assessment of lumbosacral plexus nerve root lesions.

METHODS

Seventy-two subjects underwent MENSA and CUBE sequences on a 3.0-T MRI scanner. Two musculoskeletal radiologists independently assessed the images for quality and diagnostic capability. A qualitative assessment scoring system for image quality and quantitative nerve signal-to-noise ratio (SNR) and iliac vein and muscle contrast-to-noise ratios (CNR) was applied. Using surgical reports as the reference, sensitivity, specificity, accuracy, and area under the receiver operating characteristic curves (AUC) were evaluated. Intraclass correlation coefficients (ICC) and weighted kappa were used to calculate reliability.

RESULTS

MENSA image quality rating (3.679 ± 0.47) was higher than for CUBE images (3.038 ± 0.68), and MENSA showed higher mean nerve root SNR (36.935 ± 8.33 vs. 27.777 ± 7.41), iliac vein CNR (24.678 ± 6.63 vs. 5.210 ± 3.93), and muscle CNR (19.414 ± 6.07 vs. 13.531 ± 0.65) than CUBE (P < 0.05). Weighted kappa and ICC values indicated good reliability. Sensitivity, specificity, and accuracy of diagnosis based on MENSA images were 96.23%, 89.47%, and 94.44%, respectively, and AUC was 0.929, compared with 92.45%, 84.21%, 90.28%, and 0.883 for CUBE images. The two correlated ROC curves were not significantly different. Weighted kappa values for intraobserver (0.758) and interobserver (0.768-0.818) reliability were substantial to perfect.

CONCLUSION

A time-efficient 4-min MENSA protocol exhibits superior image quality and high vascular contrast with the potential to produce high-resolution lumbosacral nerve root images.

The QIBA Profile for MRI-based Compositional Imaging of Knee Cartilage

MRI-based cartilage compositional analysis shows biochemical and microstructural changes at early stages of osteoarthritis before changes become visible with structural MRI sequences and arthroscopy. This could help with early diagnosis, risk assessment, and treatment monitoring of osteoarthritis. Spin-lattice relaxation time constant in rotating frame (T1ρ) and T2 mapping are the MRI techniques best established for assessing cartilage composition. Only T2 mapping is currently commercially available, which is sensitive to water, collagen content, and orientation of collagen fibers, whereas T1ρ is more sensitive to proteoglycan content. Clinical application of cartilage compositional imaging is limited by high variability and suboptimal reproducibility of the biomarkers, which was the motivation for creating the Quantitative Imaging Biomarkers Alliance (QIBA) Profile for cartilage compositional imaging by the Musculoskeletal Biomarkers Committee of the QIBA. The profile aims at providing recommendations to improve reproducibility and to standardize cartilage compositional imaging. The QIBA Profile provides two complementary claims (summary statements of the technical performance of the quantitative imaging biomarkers that are being profiled) regarding the reproducibility of biomarkers. First, cartilage T1ρ and T2 values are measurable at 3.0-T MRI with a within-subject coefficient of variation of 4%-5%. Second, a measured increase or decrease in T1ρ and T2 of 14% or more indicates a minimum detectable change with 95% confidence. If only an increase in T1ρ and T2 values is expected (progressive cartilage degeneration), then an increase of 12% represents a minimum detectable change over time. The QIBA Profile provides recommendations for clinical researchers, clinicians, and industry scientists pertaining to image data acquisition, analysis, and interpretation and assessment procedures for T1ρ and T2 cartilage imaging and test-retest conformance. This special report aims to provide the rationale for the proposed claims, explain the content of the QIBA Profile, and highlight the future needs and developments for MRI-based cartilage compositional imaging for risk prediction, early diagnosis, and treatment monitoring of osteoarthritis.

3D MRI of Articular Cartilage

Osteoarthritis, characterized by the breakdown of articular cartilage and other joint structures, is one of the most prevalent and disabling chronic diseases in the United States. Magnetic resonance imaging is a commonly used imaging modality to evaluate patients with joint pain. Both two-dimensional fast spin-echo sequences (2D-FSE) and three-dimensional (3D) sequences are used in clinical practice to evaluate articular cartilage. The 3D sequences have many advantages compared with 2D-FSE sequences, such as their high in-plane spatial resolution, thin continuous slices that reduce the effects of partial volume averaging, and ability to create multiplanar reformat images following a single acquisition. This article reviews the different 3D imaging techniques available for evaluating cartilage morphology, illustrates the strengths and weaknesses of 3D approaches compared with 2D-FSE approaches for cartilage imaging, and summarizes the diagnostic performance of 2D-FSE and 3D sequences for detecting cartilage lesions within the knee and hip joints.

Knee Cartilage Imaging

Articular cartilage injury and degeneration represent common causes of knee pain, which can be evaluated accurately and noninvasively using MRI. This review describes the structure of cartilage focusing on its histologic appearance to emphasize that structure will dictate patterns of tissue failure as well as MR appearance. In addition to identifying cartilage loss, MRI can demonstrate signal changes that correspond to intrinsic structural abnormalities which place the cartilage at risk for subsequent more serious injury or premature degeneration, allowing for earlier intervention and treatment of important causes of pain and morbidity.

Morphological MRI of knee cartilage: repeatability and reproducibility of damage evaluation and correlation with gross pathology examination

OBJECTIVE

To assess the performance of a morphological evaluation, based on a clinically relevant magnetic resonance imaging (MRI) protocol, in scoring the severity of knee cartilage damage. Specifically, to evaluate the reproducibility, repeatability, and agreement of MRI evaluation with the gross pathology examination (GPE) of the tissue.

METHODS

MRI of the knee was performed the day before surgery in 23 patients undergoing total knee arthroplasty. Osteochondral tissue resections were collected and chondral defects were scored by GPE according to a semi-quantitative scale. MR images were independently scored by four radiologists, who assessed the severity of chondral damage according to equivalent criteria. Inter- and intra-rater agreements of MRI evaluations were assessed. Correlation, precision, and accuracy metrics between MRI and GPE scores were calculated.

RESULTS

Moderate to substantial inter-rater agreement in scoring cartilage damage by MRI was found among radiologists. Intra-rater agreement was higher than 96%. A significant positive monotonic correlation between GPE and MRI scores was observed for all radiologists, although higher correlation values were obtained by radiologists with expertise in musculoskeletal radiology and/or longer experience. The accuracy of MRI scores displayed a spatial pattern, characterized by lesion overestimation in the lateral condyle and underestimation in the medial condyle with respect to GPE.

CONCLUSIONS

Evaluation of knee cartilage morphology by MRI is a reproducible and repeatable technique, which positively correlates with GPE. Clinical expertise in musculoskeletal radiology positively impacts the evaluation reliability. These findings may help to address limitations in MRI evaluation of knee chondral lesions, thus improving MRI assessment of knee cartilage.

KEY POINTS

• MRI evaluation of knee cartilage shows moderate to strong correlation with gross pathology examination. • MRI evaluation overestimates cartilage damage in the lateral condyle and underestimates it in the medial condyle. • Education and experience of the radiologist play a role in MRI evaluation of knee chondral lesions.

Routine clinical knee MR reports: comparison of diagnostic performance at 1.5 T and 3.0 T for assessment of the articular cartilage

OBJECTIVE

Accurate assessment of knee articular cartilage is clinically important. Although 3.0 Tesla (T) MRI is reported to offer improved diagnostic performance, literature regarding the clinical impact of MRI field strength is lacking. The purpose of this study is to compare the diagnostic performance of clinical MRI reports for assessment of cartilage at 1.5 and 3.0 T in comparison to arthroscopy.

MATERIALS AND METHODS

This IRB-approved retrospective study consisted of 300 consecutive knees in 297 patients who had routine clinical MRI and arthroscopy. Descriptions of cartilage from MRI reports of 165 knees at 1.5 T and 135 at 3.0 T were compared with arthroscopy. The sensitivity, specificity, percent of articular surfaces graded concordantly, and percent of articular surfaces graded within one grade of the arthroscopic grading were calculated for each articular surface at 1.5 and 3.0 T. Agreement between MRI and arthroscopy was calculated with the weighted-kappa statistic. Significance testing was performed utilizing the z-test after bootstrapping to obtain the standard error.

RESULTS AND CONCLUSIONS

The sensitivity, specificity, percent of articular surfaces graded concordantly, and percent of articular surfaces graded within one grade were 61.4%, 82.7%, 62.2%, and 77.5% at 1.5 T and 61.8%, 80.6%, 59.5%, and 75.6% at 3.0 T, respectively. The weighted kappa statistic was 0.56 at 1.5 T and 0.55 at 3.0 T. There was no statistically significant difference in any of these parameters between 1.5 and 3.0 T. Factors potentially contributing to the lack of diagnostic advantage of 3.0 T MRI are discussed.

Comparing an accelerated 3D fast spin-echo sequence (CS-SPACE) for knee 3-T magnetic resonance imaging with traditional 3D fast spin-echo (SPACE) and routine 2D sequences

PURPOSE

To compare a faster, new, high-resolution accelerated 3D-fast-spin-echo (3D-FSE) acquisition sequence (CS-SPACE) to traditional 2D and high-resolution 3D sequences for knee 3-T magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Twenty patients received knee MRIs that included routine 2D (T1, PD ± FS, T2-FS; 0.5 × 0.5 × 3 mm³; ∼10 min), traditional 3D FSE (SPACE-PD-FS; 0.5 × 0.5 × 0.5 mm³; ∼7.5 min), and accelerated 3D-FSE prototype (CS-SPACE-PD-FS; 0.5 × 0.5 × 0.5 mm³; ∼5 min) acquisitions on a 3-T MRI system (Siemens MAGNETOM Skyra). Three musculoskeletal radiologists (MSKRs) prospectively and independently reviewed the studies with graded surveys comparing image and diagnostic quality. Tissue-specific signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were also compared.

RESULTS

MSKR-perceived diagnostic quality of cartilage was significantly higher for CS-SPACE than for SPACE and 2D sequences (p < 0.001). Assessment of diagnostic quality of menisci and synovial fluid was higher for CS-SPACE than for SPACE (p < 0.001). CS-SPACE was not significantly different from SPACE but had lower assessments than 2D sequences for evaluation of bones, ligaments, muscles, and fat (p ≤ 0.004). 3D sequences had higher spatial resolution, but lower overall assessed contrast (p < 0.001). Overall image quality from CS-SPACE was assessed as higher than SPACE (p = 0.007), but lower than 2D sequences (p < 0.001). Compared to SPACE, CS-SPACE had higher fluid SNR and CNR against all other tissues (all p < 0.001).

CONCLUSIONS

The CS-SPACE prototype allows for faster isotropic acquisitions of knee MRIs over currently used protocols. High fluid-to-cartilage CNR and higher spatial resolution over routine 2D sequences may present a valuable role for CS-SPACE in the evaluation of cartilage and menisci.

A narrative overview of the current status of MRI of the hip and its relevance for osteoarthritis research - what we know, what has changed and where are we going?

OBJECTIVE

To review and discuss the role of magnetic resonance imaging (MRI) in the context of hip osteoarthritis (OA) research.

DESIGN

The content of this narrative review, based on an extensive PubMed database research including English literature only, describes the advances in MRI of the hip joint and its potential usefulness in hip OA research, reviews the relevance of different MRI features in regard to symptomatic and structural progression in hip OA, and gives an outlook regarding future use of MRI in hip OA research endeavors.

RESULTS

Recent technical advances have helped to overcome many of the past difficulties related to MRI assessment of hip OA. MRI-based morphologic scoring systems allow for detailed assessment of several hip joint tissues and, in combination with the recent advances in MRI, may increase reproducibility and sensitivity to change. Compositional MRI techniques may add to our understanding of disease onset and progression. Knowledge about imaging pitfalls and anatomical variants is crucial to avoid misinterpretation. In comparison to research on knee OA, the associations between MRI features and the incidence and progression of disease as well as with clinical symptoms have been little explored. Anatomic alterations of the hip joint as seen in femoro-acetabular impingement (FAI) seem to play a role in the onset and progression of structural damage.

CONCLUSIONS

With the technical advances occurring in recent years, MRI may play a major role in investigating the natural history of hip OA and provide an improved method for assessment of the efficacy of new therapeutic approaches.

Water Selective Imaging and bSSFP Banding Artifact Correction in Humans and Small Animals at 3T and 7T, Respectively

INTRODUCTION

The purpose of this paper is to develop an easy method to generate both fat signal and banding artifact free 3D balanced Steady State Free Precession (bSSFP) images at high magnetic field.

METHODS

In order to suppress fat signal and bSSFP banding artifacts, two or four images were acquired with the excitation frequency of the water-selective binomial radiofrequency pulse set On Resonance or shifted by a maximum of 3/4TR. Mice and human volunteers were imaged at 7 T and 3 T, respectively to perform whole-body and musculoskeletal imaging. "Sum-Of-Square" reconstruction was performed and combined or not with parallel imaging.

RESULTS

The frequency selectivity of 1-2-3-2-1 or 1-3-3-1 binomial pulses was preserved after (3/4TR) frequency shifting. Consequently, whole body small animal 3D imaging was performed at 7 T and enabled visualization of small structures within adipose tissue like lymph nodes. In parallel, this method allowed 3D musculoskeletal imaging in humans with high spatial resolution at 3 T. The combination with parallel imaging allowed the acquisition of knee images with ~500 μm resolution images in less than 2 min. In addition, ankles, full head coverage and legs of volunteers were imaged, demonstrating the possible application of the method also for large FOV.

CONCLUSION

In conclusion, this robust method can be applied in small animals and humans at high magnetic fields. The high SNR and tissue contrast obtained in short acquisition times allows to prescribe bSSFP sequence for several preclinical and clinical applications.

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.

OARSI Clinical Trials Recommendations: Knee imaging in clinical trials in osteoarthritis

Significant advances have occurred in our understanding of the pathogenesis of knee osteoarthritis (OA) and some recent trials have demonstrated the potential for modification of the disease course. The purpose of this expert opinion, consensus driven exercise is to provide detail on how one might use and apply knee imaging in knee OA trials. It includes information on acquisition methods/techniques (including guidance on positioning for radiography, sequence/protocol recommendations/hardware for magnetic resonance imaging (MRI)); commonly encountered problems (including positioning, hardware and coil failures, sequences artifacts); quality assurance (QA)/control procedures; measurement methods; measurement performance (reliability, responsiveness, validity); recommendations for trials; and research recommendations.

OARSI Clinical Trials Recommendations: Hip imaging in clinical trials in osteoarthritis

Imaging of hip in osteoarthritis (OA) has seen considerable progress in the past decade, with the introduction of new techniques that may be more sensitive to structural disease changes. The purpose of this expert opinion, consensus driven recommendation is to provide detail on how to apply hip imaging in disease modifying clinical trials. It includes information on acquisition methods/techniques (including guidance on positioning for radiography, sequence/protocol recommendations/hardware for magnetic resonance imaging (MRI)); commonly encountered problems (including positioning, hardware and coil failures, artifacts associated with various MRI sequences); quality assurance/control procedures; measurement methods; measurement performance (reliability, responsiveness, and validity); recommendations for trials; and research recommendations.

Morphological MR imaging of the articular cartilage of the knee at 3 T-comparison of standard and novel 3D sequences

Objectives

This study sought to compare various 3D cartilage sequences and to evaluate the usefulness of ultrashort TE (UTE) imaging, a new technique to isolate signal from the osteochondral junction.

Methods

Twenty knees were examined at 3 T with 3D spoiled GRE (FLASH), double-echo steady-state (DESS), balanced SSFP, 3D turbo spin-echo (TSE), and a prototype UTE sequence. Two radiologists independently evaluated all images. Consensus readings of all sequences were the reference standard. Statistical analysis included Friedman and pairwise Wilcoxon tests. Retrospective analysis of UTE morphology of osteochondral tissue in normal and abnormal cartilage seen at conventional MR was also performed.

Results

Three-dimensional TSE was superior to other sequences for detecting cartilage lesions. FLASH and DESS performed best in the subjective quality analysis. On UTE images, normal cartilage exhibited a high-intensity linear signal near the osteochondral junction. Retrospective analysis revealed abnormal UTE morphology of the osteochondral junction in 50 % of cartilage lesions diagnosed at conventional MR.

Conclusions

Cartilage imaging of the knee at 3 T can be reliably performed using 3D TSE, showing high accuracy when compared to standard sequences. Although UTE depicts signal from the deep cartilage layer, further studies are needed to establish its role for assessment of cartilage.

Main Messages

• MRI is the best available imaging method for assessment of knee cartilage.

• Cartilage imaging can be reliably performed using 3D TSE.

• UTE cannot be used as a single sequence to assess cartilage.

Optimizing isotropic three-dimensional fast spin-echo methods for imaging the knee

PURPOSE

To optimize acquisition parameters for three dimensional fast spin-echo (3D FSE) imaging of the knee.

MATERIALS AND METHODS

The knees of eight healthy volunteers were imaged in a 3 Tesla MRI scanner using an eight-channel knee coil. A total of 146 intermediate weighted isotropic resolution 3D FSE (3D-FSE-Cube)images with varied acquisition parameter settings were acquired with an additional reference scan performed for subjective image quality assessment. Images were graded for overall quality, parallel imaging artifact severity and blurring. Cartilage, muscle, and fluid signal-to-noise ratios and fluid-cartilage contrast-to-noise ratios were quantified by acquiring scans without radio frequency excitation and custom-reconstructing the k-space data.Mixed effects regression modeling was used to determine statistically significant effects of different parameters on image quality.

RESULTS

Changes in receiver bandwidth, repetition time and echo train length significantly affected all measurements of image quality (P < 0.05). Reducing band width improved all metrics of image quality with the exception of blurring. Reader agreement was slight to fair for subjective metrics, but overall trends in quality ratings were apparent.

CONCLUSION

We used a systematic approach to optimize 3D-FSE-Cube parameters for knee imaging. Image quality was overall improved using a receiver bandwidth of 631.25 kHz, and blurring increased with lower band width and longer echo trains.

Rapid isotropic resolution cartilage assessment using radial alternating repetition time balanced steady-state free-precession imaging

PURPOSE

To compare a balanced steady-state free-precession sequence with a radial k-space trajectory and alternating repetition time fat suppression (Radial-ATR) with other currently used fat-suppressed 3D sequences for evaluating the articular cartilage of the knee joint at 3.0T.

MATERIALS AND METHODS

Radial-ATR, fast spin-echo (FSE-Cube), gradient recall-echo acquired in the steady-state (GRASS), and spoiled gradient recall-echo (SPGR) sequences with similar voxel volumes and identical scan times were performed at 3.0T on both knee joints of five volunteers. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements were performed for all sequences using a double acquisition method and compared using Mann-Whitney Wilcoxon tests. Radial-ATR sequences with 0.3 mm and 0.4 mm isotropic resolution were also performed on the knee joints of seven volunteers and three patients with osteoarthritis.

RESULTS

Average SNR values for cartilage, synovial fluid, and bone marrow were 54.7, 153.3, and 12.9, respectively, for Radial ATR, 30.8, 44.1, and 1.9, respectively, for FSE-Cube, 13.3, 46.9, and 3.3, respectively, for GRASS, and 19.1, 8.1, and 2.1, respectively, for SPGR. Average CNR values between cartilage and synovial fluid and between cartilage and bone marrow were 98.6 and 41.8, respectively, for VIPR-ATR, 13.4 and 28.8, respectively, for FSE-Cube, 33.6 and 10.0, respectively, for GRASS, and 11.0 and 16.9, respectively, for SPGR. Radial-ATR had significantly higher (P < 0.001) cartilage, synovial fluid, and bone marrow SNR and significantly higher (P < 0.01) CNR between cartilage and synovial fluid and between cartilage and bone marrow than FSE-Cube, GRASS, and SPGR. Radial-ATR provided excellent visualization of articular cartilage at high isotropic resolution with no image degradation due to off-resonance banding artifacts.

CONCLUSION

Radial-ATR had superior SNR efficiency to other fat-suppressed 3D cartilage imaging sequences and produced high isotropic resolution images of the knee joint which could be used for evaluating articular cartilage at 3.0T.

A historical overview of magnetic resonance imaging, focusing on technological innovations

Magnetic resonance imaging (MRI) has now been used clinically for more than 30 years. Today, MRI serves as the primary diagnostic modality for many clinical problems. In this article, historical developments in the field of MRI will be discussed with a focus on technological innovations. Topics include the initial discoveries in nuclear magnetic resonance that allowed for the advent of MRI as well as the development of whole-body, high field strength, and open MRI systems. Dedicated imaging coils, basic pulse sequences, contrast-enhanced, and functional imaging techniques will also be discussed in a historical context. This article describes important technological innovations in the field of MRI, together with their clinical applicability today, providing critical insights into future developments.

Diagnostic performance of CUBE MRI sequences of the knee compared with conventional MRI

AIM

To evaluate the efficacy and efficiency of three-dimensional (3D) fast spin-echo (FSE) with variable flip angle ("CUBE") magnetic resonance imaging (MRI) in knee imaging as compared with conventional MRI.

MATERIALS AND METHODS

Twenty-nine patients (single knee) with joint injuries of varying degrees were enrolled in this study between January, 2011 and December, 2011. All patients underwent conventional MRI and a fat-suppressed CUBE MRI sequence. All patients subsequently underwent knee arthroscopic surgery performed by an experienced orthopaedic surgeon within 2 weeks after the MRI examinations. With standard reference provided by arthroscopic results, the sensitivity, specificity, and accuracy of both the CUBE and conventional MRI techniques were calculated for detecting cartilage lesions, meniscus tears, and anterior cruciate ligament injuries, respectively. A chi-square test was used for statistical analysis with a level of significance of p < 0.05.

RESULTS

For the evaluation of articular cartilage lesions, the CUBE sequence had higher sensitivity (70.9% versus 50.6%, p < 0.01), higher specificity (72.6% versus 58.9%, p < 0.05), and higher accuracy (71.8% versus 55.2%, p = 0.001) than conventional MRI. For the evaluation of meniscus tears, CUBE and conventional MRI had similar sensitivity, specificity, and accuracy (p = 0.20-0.55). Similarly, there was no significant difference in sensitivity, specificity, or accuracy between CUBE imaging and conventional imaging in the detection of anterior cruciate ligament injuries (p = 0.13-0.65).

CONCLUSION

CUBE MRI has similar or superior sensitivity, specificity, and accuracy to a conventional imaging protocol in the comprehensive evaluation of knee joint injuries.

Spin-lattice relaxation rates and water content of freeze-dried articular cartilage

OBJECTIVE

Nuclear magnetic resonance (NMR) spin-lattice relaxation rates were measured in bovine and porcine articular cartilage as a function of water content.

METHODS

Water content was varied by freeze-drying samples for short periods of time (up to 15 min). The samples were weighed at all stages of drying so that water content could be quantified. Spin-lattice relaxation rates were measured using magnetic resonance imaging (MRI).

RESULTS

Linear correlations were observed between relaxation rate and two measures of inverse water content: (1) solid-to-water ratio (ρ), expressed as a ratio of the mass of the solid component of the cartilage (m(s)) and the mass of water at each freeze-drying time point (m(w)), and (2) a ratio of the total mass of the fully-hydrated cartilage and m(w) (1/w). These correlations did not appear significantly different for the bovine and porcine data. However, fitting the data to a piecewise-linear model revealed differences between these two species. We interpret the first two segments of the piecewise model as the depletion of different water phases but conjecture that the third segment is partially caused by changes in relaxation rates as a result of a reduction in macromolecular mobilities.

CONCLUSIONS

Whilst we can produce linear correlations which broadly describe the dependence of the measured spin-lattice relaxation rate on (inverse) water content, the linear model seems to obscure a more complicated relationship which potentially provides us with more information about the structure of articular cartilage and its extracellular water.

Comparison of three-dimensional isotropic T1-weighted fast spin-echo MR arthrography with two-dimensional MR arthrography of the shoulder

PURPOSE

To determine the accuracy of a three-dimensional (3D) isotropic T1-weighted fast spin-echo (FSE) magnetic resonance (MR) sequence as compared with a conventional two-dimensional (2D) sequence in the diagnosis of rotator cuff tears and labral lesions.

MATERIALS AND METHODS

Institutional review board approval was obtained, and the informed consent requirement was waived. Forty-nine patients who had undergone direct or indirect shoulder MR arthrography with the 2D T1-weighted FSE sequence and the 3D isotropic T1-weighted FSE sequence and subsequent arthroscopy were included. Each MR imaging sequence was independently scored by two readers retrospectively for the presence of full- or partial-thickness tears of the supraspinatus (SST) and infraspinatus (IST) tendons and the subscapularis tendon (SCT) and labral lesions. Diagnostic performance based on each sequence type was compared by using the area under the receiver operating characteristic curve (AUC).

RESULTS

Arthroscopic findings enabled confirmation of the presence of 17 full-thickness SST-IST tears, 18 partial-thickness SST-IST tears, four full-thickness SCT tears, 17 partial-thickness SCT tears, and 17 labral lesions. The AUCs for the readers using the 3D T1-weighted FSE sequence versus those obtained with the 2D sequence were 0.771-0.989 versus 0.837-0.998 for reader A and 0.771-0.989 versus 0.797-0.989 for reader B in the detection of rotator cuff tears and 0.885 versus 0.897 for reader A and 0.895 versus 0.895 for reader B in the detection of labral lesions. The mean AUCs between the 2D and 3D sequences were not significantly different, with the exception of partial-thickness SCT tears for one reader.

CONCLUSION

The accuracy of 3D isotropic FSE MR arthrography may be comparable with that of conventional 2D MR arthrography in the diagnosis of rotator cuff tears and labral lesions with a shorter imaging time.

Three-dimensional magnetic resonance imaging of joints

Magnetic resonance (MR) imaging is one of the most commonly used imaging modality for evaluating patients with joint pain. Musculoskeletal MR protocols at most institutions consist of 2-dimensional fast spin echo (FSE) sequences repeated in multiple planes. Three-dimensional sequences have also been used to evaluate the musculoskeletal system and have many potential advantages over 2-dimensional FSE sequences. Three-dimensional sequences acquire thin continuous slices through joints with high in-plane spatial resolution, which minimize the effects of partial volume averaging. Newly developed 3-dimensional isotropic resolution sequences can also be used to create high-quality multiplanar reformat images that allow joints to be evaluated in any orientation after a single acquisition. Preliminary results on the use of 3-dimensional isotropic resolution sequences for evaluating the musculoskeletal system are encouraging. However, additional studies are needed to document the advantages of 3-dimensional sequences before they can replace currently used 2-dimensional FSE sequences for evaluating the musculoskeletal system in clinical practice.