Articular cartilage of the knee: rapid three-dimensional MR imaging at 3.0 T with IDEAL balanced steady-state free precession--initial experience

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.

Protective therapeutic effects of peptide nanofiber and hyaluronic acid hybrid membrane in in vivo osteoarthritis model

Osteoarthritis (OA) is a condition where tissue function is lost through a combination of secondary inflammation and deterioration in articular cartilage. One of the most common causes of OA is age-related tissue impairment because of wear and tear due to mechanical erosion. Hyaluronic acid-based viscoelastic supplements have been widely used for the treatment of knee injuries. However, the current formulations of hyaluronic acid are unable to provide efficient healing and recovery. Here, a nanofiber-hyaluronic acid membrane system that was prepared by using a quarter of the concentration of commercially available hyaluronic acid supplement, Hyalgan®, was used for the treatment of an osteoarthritis model, and Synvisc®, which is another commercially available hyaluronic acid containing viscoelastic supplement, was used as a control. The results show that this system provides efficient protection of arthritic cartilage tissue through the preservation of cartilage morphology with reduced osteophyte formation, protection of the subchondral region from deterioration, and maintenance of cartilage specific matrix proteins in vivo. In addition, the hybrid nanofiber membrane enabled chondrocyte encapsulation and provided a suitable culturing environment for stem cell growth in vitro. Overall, our results suggest that this hybrid nanofibrous scaffold provides a potential platform the treatment of OA.

STATEMENT OF SIGNIFICANCE

Osteoarthritis is a debilitating joint disease affecting millions of people worldwide. It occurs especially in knees due to aging, sport injuries or obesity. Although hyaluronic acid-based viscoelastic supplements are widely used, there is still no effective treatment method for osteoarthritis, which necessitates surgical operation as an only choice for severe cases. Therefore, there is an urgent need for efficient therapeutics. In this study, a nanofiber-HA membrane system was developed for the efficient protection of arthritic cartilage tissue from degeneration. This hybrid nanofiber system provided superior therapeutic activity at a relatively lower concentration of hyaluronic acid than Hyalgan® and Synvisc® gels, which are currently used in clinics. This work demonstrates for the first time that this hybrid nanofiber membrane scaffold can be utilized as a potential candidate for osteoarthritis treatment.

Fabrication of Custom-Shaped Grafts for Cartilage Regeneration

Purpose

to create a custom-shaped graft through 3D tissue shape reconstruction and rapid-prototype molding methods using MRI data, and to test the accuracy of the custom-shaped graft against the original anatomical defect.

Methods

An iatrogenic defect on the distal femur was identified with a 1.5 Tesla MRI and its shape was reconstructed into a three-dimensional (3D) computer model by processing the 3D MRI data. First, the accuracy of the MRI-derived 3D model was tested against a laser-scan based 3D model of the defect. A custom-shaped polyurethane graft was fabricated from the laser-scan based 3D model by creating custom molds through computer aided design and rapid-prototyping methods. The polyurethane tissue was laser-scanned again to calculate the accuracy of this process compared to the original defect.

Results

The volumes of the defect models from MRI and laser-scan were 537 mm3 and 405 mm3, respectively, implying that the MRI model was 33% larger than the laser-scan model. The average (±SD) distance deviation of the exterior surface of the MRI model from the laser-scan model was 0.4±0.4 mm. The custom-shaped tissue created from the molds was qualitatively very similar to the original shape of the defect. The volume of the custom-shaped cartilage tissue was 463 mm3 which was 15% larger than the laser-scan model. The average (±SD) distance deviation between the two models was 0.04±0.19 mm.

Conclusions

This investigation proves the concept that custom-shaped engineered grafts can be fabricated from standard sequence 3-D MRI data with the use of CAD and rapid-prototyping technology. The accuracy of this technology may help solve the interfacial problem between native cartilage and graft, if the grafts are custom made for the specific defect. The major source of error in fabricating a 3D custom-shaped cartilage graft appears to be the accuracy of a MRI data itself; however, the precision of the model is expected to increase by the utilization of advanced MR sequences with higher magnet strengths.

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.

Approach to MR Imaging of the Elbow and Wrist: Technical Aspects and Innovation

Wrist and elbow MR imaging technology is advancing at a dramatic rate. Wrist and elbow MR imaging is performed at medium and higher field strengths with more specialized surface coils and more variable pulse sequences and postprocessing techniques. High field imaging and improved coils lead to an increased signal-to-noise ratio and increased variety of soft tissue contrast options. Three-dimensional imaging is improving in terms of usability and artifacts. Some of these advances have challenges in wrist and elbow imaging, such as postoperative patient imaging, cartilage mapping, and molecular imaging. This review considers technical advances in hardware and software and their clinical applications.

Fat-suppression techniques for 3-T MR imaging of the musculoskeletal system

Fat suppression is an important technique in musculoskeletal imaging to improve the visibility of bone-marrow lesions; evaluate fat in soft-tissue masses; optimize the contrast-to-noise ratio in magnetic resonance (MR) arthrography; better define lesions after administration of contrast material; and avoid chemical shift artifacts, primarily at 3-T MR imaging. High-field-strength (eg, 3-T) MR imaging has specific technical characteristics compared with lower-field-strength MR imaging that influence the use and outcome of various fat-suppression techniques. The most commonly used fat-suppression techniques for musculoskeletal 3-T MR imaging include chemical shift (spectral) selective (CHESS) fat saturation, inversion recovery pulse sequences (eg, short inversion time inversion recovery [STIR]), hybrid pulse sequences with spectral and inversion-recovery (eg, spectral adiabatic inversion recovery and spectral attenuated inversion recovery [SPAIR]), spatial-spectral pulse sequences (ie, water excitation), and the Dixon techniques. Understanding the different fat-suppression options allows radiologists to adopt the most appropriate technique for their clinical practice.

The role of radiology in the evolution of the understanding of articular disease

Both the clinical practice of radiology and the journal Radiology have had an enormous effect on our understanding of articular disease. Early descriptions of osteoarthritis (OA) appeared in Radiology. More recently, advanced physiologic magnetic resonance (MR) techniques have furthered our understanding of the early prestructural changes in patients with OA. Sodium imaging, delayed gadolinium-enhanced MR imaging of cartilage, and spin-lattice relaxation in the rotating frame (or T1ρ) sequences have advanced understanding of the pathophysiology and pathoanatomy of OA. Many pioneering articles on rheumatoid arthritis (RA) also have been published in Radiology. In the intervening decades, our understanding of the natural history of RA has been altered by these articles. Many of the first descriptions of crystalline arthropathies, including gout, calcium pyrophosphate deposition, and hydroxyapatite deposition disease, appeared in Radiology.

MR imaging of articular cartilage at 1.5T and 3.0T: comparison of IDEAL 2D FSE and 3D SPGR with fat-saturated 2D FSE and 3D SPGR in a porcine model

BACKGROUND

IDEAL technique is a robust fat-water separation method which is potentially useful in cartilage imaging with significant improvement in the cartilage signal-to-noise ratio (SNR).

PURPOSE

To identify whether iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) improved diagnostic performance for IDEAL 2D fast spin echo (FSE) and 3D spoiled gradient-recalled echo (SPGR) versus fat-saturated (FS) protocols at 1.5 and 3.0 T in the evaluation of patella-femoral cartilage lesions.

MATERIAL AND METHODS

Forty-six artificial cartilage lesions were created in femoro-patellar articular cartilages of 11 porcine knees. All knees underwent MR examination at 1.5 and 3.0 T with MR protocol consisting of sagittal FS 2D FSE and 3D SPGR and IDEAL 2D FSE and IDEAL 3D SPGR, respectively. Qualitative assessment was performed to compare the diagnostic performance between 1.5- and 3.0-T protocols and between IDEAL and FS protocols.

RESULTS

IDEAL 3D SPGR had a significantly higher accuracy for detecting partial thickness cartilage lesions (P < 0.01) than FS SPGR protocols, whereas there was no significant difference in diagnostic performance between IDEAL and FS 2D FSE except for one cartilage lesion. For all imaging sequences, no significant difference was observed in the diagnostic performance between 1.5- and 3.0-T imaging protocols (P = 0.42-0.91).

CONCLUSION

Compared with conventional FS SPGR imaging, IDEAL 3D SPGR provided a better diagnostic performance for evaluation of porcine knee articular cartilage lesions in the knee joints at 1.5 and 3.0 T. IDEAL 3D SPGR may therefore be useful for detecting partial-thickness cartilage lesions in patients with degenerative osteoarthritis.

MR-guided sclerotherapy of low-flow vascular malformations using T2 -weighted interrupted bSSFP (T2 W-iSSFP): comparison of pulse sequences for visualization and needle guidance

PURPOSE

Image-guided treatment of low-flow vascular (venous or lymphatic) malformations presents a challenging visualization problem, regardless of the imaging modality being used for guidance. The purpose of this study was to employ a new magnetic resonance imaging (MRI) sequence, T2 -weighted interrupted balanced steady-state free precession (T2 W-iSSFP), for real-time image guidance of needle insertion.

MATERIALS AND METHODS

T2 W-iSSFP uses variable flip angle balanced steady-state free precession (bSSFP, a.k.a. SSFP) to establish T2 -weighting and fat suppression. Swine (n = 3) and patients (n = 4, three female, all with venous malformations) were enrolled in the assessment. T2 -weighted turbo spin echo (T2 -TSE) with spectral adiabatic inversion recovery (SPAIR), SPAIR-T2 -TSE or T2 -TSE for short, was used as the reference. T2 -weighted half Fourier acquired single shot turbo spin echo (T2 -HASTE) with SPAIR (SPAIR-T2 -HASTE, T2 -HASTE for short), fat saturated bSSFP (FS-SSFP), and T2 W-iSSFP were imaged. Numeric metrics, namely, contrast-to-noise ratio (CNR) efficiency (CNR divided by the square root of acquisition time) and local sharpness (the reciprocal of edge width), were used to assess image quality. MR-guided sclerotherapy was performed on the same patients using real-time T2 W-iSSFP to guide needle insertion.

RESULTS

Comparing the visualization of needles in the images of swine, the local sharpness (mm(-1) ) was: 0.21 ± 0.06 (T2 -HASTE), 0.48 ± 0.02 (FS-SSFP), and 0.49 ± 0.03 (T2 W-iSSFP). T2 W-iSSFP is higher than T2 -HASTE (P < 0.001). For the patient images, their CNR efficiencies were: 797 ± 66 (T2 -HASTE), 281 ± 44 (FS-SSFP), and 860 ± 29 (T2 W-iSSFP). T2 W-iSSFP is higher than FS-SSFP (P < 0.02). The frame rate of T2 W-iSSFP was 2.5-3.5 frames per second. All MR-guided sclerotherapy procedures were successful, with all needles (six punctures) placed in the targets.

CONCLUSION

T2 W-iSSFP provides effective lesion identification and needle visualization. This new pulse sequence can be used for MR-guided sclerotherapy of low-flow vascular malformations. It may have potential use in other MR-guided procedures where heavily T2 -weighted real-time images are needed.

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.

Magnetic resonance imaging of pediatric muscular disorders: recent advances and clinical applications

This review describes various quantitative magnetic resonance imaging techniques that can be used to objectively analyze the composition (T2 relaxation time mapping, Dixon imaging, and diffusion-weighted imaging), architecture (diffusion tensor imaging), mechanical properties (magnetic resonance elastography), and function (magnetic resonance spectroscopy) of normal and pathologic skeletal muscle in the pediatric population.

3D T2-weighted spin echo imaging in the breast

PURPOSE

To evaluate the performance of 2D versus 3D T2-weighted spin echo imaging in the breast.

MATERIALS AND METHODS

2D and 3D T2-weighted images were acquired in 25 patients as part of a clinically indicated breast magnetic resonance imaging (MRI) exam. Lesion-to-fibroglandular tissue signal ratio was measured in 16 identified lesions. Clarity of lesion morphology was assessed through a blinded review by three radiologists. Instances demonstrating the potential diagnostic contribution of 3D versus 2D T2-weighted imaging in the breast were noted through unblinded review by a fourth radiologist.

RESULTS

The lesion-to-fibroglandular tissue signal ratio was well correlated between 2D and 3D T2-weighted images (R(2)  = 0.93). Clarity of lesion morphology was significantly better with 3D T2-weighted imaging for all observers based on a McNemar test (P ≤ 0.02, P ≤ 0.01, P ≤ 0.03). Instances indicating the potential diagnostic contribution of 3D T2-weighted imaging included improved depiction of signal intensity and improved alignment between DCE and T2-weighted findings.

CONCLUSION

In this pilot study, 3D T2-weighted imaging provided comparable contrast and improved depiction of lesion morphology in the breast in comparison to 2D T2-weighted imaging. Based on these results further investigation to determine the diagnostic impact of 3D T2-weighted imaging in breast MRI is warranted.

High-resolution 3D radial bSSFP with IDEAL

Radial trajectories facilitate high-resolution balanced steady state free precession (bSSFP) because the efficient gradients provide more time to extend the trajectory in k-space. A number of radial bSSFP methods that support fat-water separation have been developed; however, most of these methods require an environment with limited B0 inhomogeneity. In this work, high-resolution bSSFP with fat-water separation is achieved in more challenging B0 environments by combining a 3D radial trajectory with the IDEAL chemical species separation method. A method to maintain very high resolution within the timing constraints of bSSFP and IDEAL is described using a dual-pass pulse sequence. The sampling of a unique set of radial lines at each echo time is investigated as a means to circumvent the longer scan time that IDEAL incurs as a multiecho acquisition. The manifestation of undersampling artifacts in this trajectory and their effect on chemical species separation are investigated in comparison to the case in which each echo samples the same set of radial lines. This new bSSFP method achieves 0.63 mm isotropic resolution in a 5-min scan and is demonstrated in difficult in vivo imaging environments, including the breast and a knee with ACL reconstruction hardware at 1.5 T.

Advances in musculoskeletal MRI: technical considerations

The technology of musculoskeletal magnetic resonance imaging (MRI) is advancing at a dramatic rate. MRI is now done at medium and higher field strengths with more specialized surface coils and with more variable pulse sequences and postprocessing techniques than ever before. These innumerable technical advances are advantageous as they lead to an increased signal-to-noise ratio and increased variety of soft-tissue contrast options. However, at the same time they potentially produce more imaging artifacts when compared with past techniques. Substantial technical advances have considerable clinical challenges in musculoskeletal radiology such as postoperative patient imaging, cartilage mapping, and molecular imaging. In this review we consider technical advances in hardware and software of musculoskeletal MRI along with their clinical applications.

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.

MR imaging of the spine at 3.0T with T2-weighted IDEAL fast recovery fast spin-echo technique

Objective

To compare the iterative decomposition of water and fat with echo asymmetry and the least-squares estimation (IDEAL) method with a fat-saturated T2-weighted (T2W) fast recovery fast spin-echo (FRFSE) imaging of the spine.

Materials and Methods

Images acquired at 3.0 Tesla (T) in 35 patients with different spine lesions using fat-saturated T2W FRFSE imaging were compared with T2W IDEAL FRFSE images. Signal-to-noise ratio (SNR)-efficiencies measurements were made in the vertebral bodies and spinal cord in the mid-sagittal plane or nearest to the mid-sagittal plane. Images were scored with the consensus of two experienced radiologists on a four-point grading scale for fat suppression and overall image quality. Statistical analysis of SNR-efficiency, fat suppression and image quality scores was performed with a paired Student's t test and Wilcoxon's signed rank test.

Results

Signal-to-noise ratio-efficiency for both vertebral body and spinal cord was higher with T2W IDEAL FRFSE imaging (p < 0.05) than with T2W FRFSE imaging. T2W IDEAL FRFSE demonstrated superior fat suppression (p < 0.01) and image quality (p < 0.01) compared to fat-saturated T2W FRFSE.

Conclusion

As compared with fat-saturated T2W FRFSE, IDEAL can provide a higher image quality, higher SNR-efficiency, and consistent, robust and uniform fat suppression. T2W IDEAL FRFSE is a promising technique for MR imaging of the spine at 3.0T.

Value of sagittal fat-suppressed proton-density fast-spin-echo of the knee joint as a limited protocol in evaluating internal knee derangements

PURPOSE

The aim of the study was to determine the accuracy and observer agreement in the assessment of internal knee derangement using sagittal fat-suppressed proton-density fast-spin-echo (FS PD-FSE) compared with combined sagittal T1-weighted spin-echo, dual-proton-density, and T2-weighted spin-echo sequences and with arthroscopy.

METHODS

One hundred eighteen patients undergoing routine knee magnetic resonance (MR) imaging had additional imaging with sagittal FS PD-FSE sequences. Menisci, cruciate ligaments, extensor tendons (ETs), bone marrow, osteoarthritic changes, soft tissue edema, joint effusion, and incidental tumors were analyzed. Magnetic resonance images were independently reviewed by 2 radiologists. Fifty patients underwent knee arthroscopy. Statistical analysis compared both imaging protocols with each other and with arthroscopy. Intrareader and interreader agreements were evaluated using κ analysis. Both protocols were compared with arthroscopy.

RESULTS

Intrareader agreement was very high except for readings of the posterior cruciate ligament, ETs, and cartilage. Intrareader agreement did not differ significantly between the 2 readers except for ETs, bone marrow, and cartilage. Interreader percent agreements were high using both protocols and were not significantly different between the 2 readers except for posterior cruciate ligament. Compared with arthroscopy, both methods showed almost identical results regarding sensitivity, specificity, positive predictive value, and negative predictive value, except for cartilage where FS PD-FSE had increased sensitivity, whereas the combined protocol had increased specificity.

CONCLUSIONS

Sagittal FS PD-FSE is comparable to our regular MR protocol in assessing internal knee derangement with an overall agreement of at least 93% on all sites except cartilage. It was also comparable to arthroscopy in assessing the cruciate ligaments and menisci, but had a low specificity for cartilaginous derangements. It can replace our 3 sagittal series comprising T1- and T2-weighted and proton-density-spin-echo sequences, hence saving time and cost.

Advanced MRI of articular cartilage

Musculoskeletal MRI is advancing rapidly, with innovative technology and significant potential for immediate clinical impact. In particular, cartilage imaging has become a topic of increasing interest as our aging population develops diseases such as osteoarthritis. Advances in MRI hardware and software have led to increased image quality and tissue contrast. Additional developments have allowed the assessment of cartilage macromolecular content, which may be crucial to the early detection of musculoskeletal diseases. This comprehensive article considers current morphological and physiological cartilage imaging techniques, their clinical applications, and their potential to contribute to future improvements in the imaging of cartilage.

Routine 3D magnetic resonance imaging of joints

Due to its high spatial resolution and excellent tissue contrast, magnetic resonance imaging (MRI) has become the most commonly used imaging method to evaluate joints. Most musculoskeletal MRI is performed using 2D fast spin-echo sequences. However, 3D sequences have also been used for joint imaging and have the advantage of acquiring thin continuous slices through joints, which reduces the effects of partial volume averaging. With recent advances in MR technology, 3D sequences with isotropic resolution have been developed. These sequences allow high-quality multiplanar reformat images to be obtained following a single acquisition, thereby eliminating the need to repeat sequences with identical tissue contrast in different planes. Preliminary results on the diagnostic performance of 3D isotropic resolution sequences are encouraging. However, additional studies are needed to determine whether these sequences can replace currently used 2D fast spin-echo sequences for providing comprehensive joint assessment in clinical practice.

The current state of imaging the articular cartilage of the upper extremity

MR imaging has increasingly been used to image joints since its inception. Historically, there has been more emphasis on the evaluation of internal derangement rather than cartilaginous disease. This article reviews cartilaginous diseases of the upper extremity emphasizing those that can be assessed using current clinical MR imaging protocols and addresses the limitations of current imaging techniques in evaluating the articular cartilage of smaller joints. It also provides a brief overview of novel techniques that may be instituted in the future to improve the diagnostic performance of MR imaging in the evaluation of the articular cartilage of the upper extremity.

Articular cartilage in the knee: current MR imaging techniques and applications in clinical practice and research

Magnetic resonance (MR) imaging is the most important imaging modality for the evaluation of traumatic or degenerative cartilaginous lesions in the knee. It is a powerful noninvasive tool for detecting such lesions and monitoring the effects of pharmacologic and surgical therapy. The specific MR imaging techniques used for these purposes can be divided into two broad categories according to their usefulness for morphologic or compositional evaluation. To assess the structure of knee cartilage, standard spin-echo (SE) and gradient-recalled echo (GRE) sequences, fast SE sequences, and three-dimensional SE and GRE sequences are available. These techniques allow the detection of morphologic defects in the articular cartilage of the knee and are commonly used in research for semiquantitative and quantitative assessments of cartilage. To evaluate the collagen network and proteoglycan content in the knee cartilage matrix, compositional assessment techniques such as T2 mapping, delayed gadolinium-enhanced MR imaging of cartilage (or dGEMRIC), T1ρ imaging, sodium imaging, and diffusion-weighted imaging are available. These techniques may be used in various combinations and at various magnetic field strengths in clinical and research settings to improve the characterization of changes in cartilage.

Clinical cartilage imaging of the knee and hip joints

OBJECTIVE

MRI is commonly used to evaluate the articular cartilage of the knee and hip joints in clinical practice. This article will discuss the advantages and limitations of currently available MRI techniques for evaluating articular cartilage.

CONCLUSION

Because of its high spatial resolution, multiplanar capability, and excellent tissue contrast, MRI is the imaging technique of choice for evaluating the articular cartilage of the knee and hip joints.

Magnetic resonance separation imaging using a divided inversion recovery technique (DIRT)

The divided inversion recovery technique is an MRI separation method based on tissue T(1) relaxation differences. When tissue T(1) relaxation times are longer than the time between inversion pulses in a segmented inversion recovery pulse sequence, longitudinal magnetization does not pass through the null point. Prior to additional inversion pulses, longitudinal magnetization may have an opposite polarity. Spatial displacement of tissues in inversion recovery balanced steady-state free-precession imaging has been shown to be due to this magnetization phase change resulting from incomplete magnetization recovery. In this paper, it is shown how this phase change can be used to provide image separation. A pulse sequence parameter, the time between inversion pulses (T180), can be adjusted to provide water-fat or fluid separation. Example water-fat and fluid separation images of the head, heart, and abdomen are presented. The water-fat separation performance was investigated by comparing image intensities in short-axis divided inversion recovery technique images of the heart. Fat, blood, and fluid signal was suppressed to the background noise level. Additionally, the separation performance was not affected by main magnetic field inhomogeneities.

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.

Fast volumetric spatial-spectral MR imaging of hyperpolarized 13C-labeled compounds using multiple echo 3D bSSFP

PURPOSE

The goal of this work was to develop a fast 3D chemical shift imaging technique for the noninvasive measurement of hyperpolarized (13)C-labeled substrates and metabolic products at low concentration.

MATERIALS AND METHODS

Multiple echo 3D balanced steady state magnetic resonance imaging (ME-3DbSSFP) was performed in vitro on a syringe containing hyperpolarized [1,3,3-2H3; 1-(13)C]2-hydroxyethylpropionate (HEP) adjacent to a (13)C-enriched acetate phantom, and in vivo on a rat before and after intravenous injection of hyperpolarized HEP at 1.5 T. Chemical shift images of the hyperpolarized HEP were derived from the multiple echo data by Fourier transformation along the echoes on a voxel by voxel basis for each slice of the 3D data set.

RESULTS

ME-3DbSSFP imaging was able to provide chemical shift images of hyperpolarized HEP in vitro, and in a rat with isotropic 7-mm spatial resolution, 93 Hz spectral resolution and 16-s temporal resolution for a period greater than 45 s.

CONCLUSION

Multiple echo 3D bSSFP imaging can provide chemical shift images of hyperpolarized (13)C-labeled compounds in vivo with relatively high spatial resolution and moderate spectral resolution. The increased signal-to-noise ratio of this 3D technique will enable the detection of hyperpolarized (13)C-labeled metabolites at lower concentrations as compared to a 2D technique.

Recent advances in MRI of articular cartilage

OBJECTIVE

MRI is the most accurate noninvasive method available to diagnose disorders of articular cartilage. Conventional 2D and 3D approaches show changes in cartilage morphology. Faster 3D imaging methods with isotropic resolution can be reformatted into arbitrary planes for improved detection and visualization of pathology. Unique contrast mechanisms allow us to probe cartilage physiology and detect changes in cartilage macromolecules.

CONCLUSION

MRI has great promise as a noninvasive comprehensive tool for cartilage evaluation.

Multiecho IDEAL gradient-echo water-fat separation for rapid assessment of cartilage volume at 1.5 T: initial experience

Institutional review board approval and informed consent were obtained for this HIPAA-compliant study. The purpose was to prospectively compare multiecho iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) gradient-echo (GRE) magnetic resonance (MR) imaging with three-dimensional fat-suppressed (FS) spoiled GRE (SPGR) MR imaging to evaluate the articular cartilage of the knee. Six healthy volunteer and 10 cadaver knees were imaged at 1.5 T. Signal-to-noise ratio (SNR), SNR efficiency, and cartilage volume were measured. SNR and SNR efficiency were significantly higher with multiecho IDEAL GRE than with FS SPGR imaging (P < .031). Both methods produced equivalent cartilage volumes (overall concordance correlation coefficient, 0.998) with high precision and accuracy. The use of a cartilage phantom confirmed high accuracy in volume measurements and high reproducibility for both methods. Multiecho IDEAL GRE provides high signal intensity in cartilage and synovial fluid and is a promising technique for imaging articular cartilage of the knee.

[3-Tesla MRI vs. arthroscopy for diagnostics of degenerative knee cartilage diseases: preliminary clinical results]

BACKGROUND

The literature contains only a few studies investigating the magnetic resonance imaging (MRI) diagnostics of degenerative cartilage diseases. Studies on MRI diagnostics of the cartilage using field strengths of 3-Tesla demonstrate promising results. To assess the value of 3-Tesla MRI for decision making regarding conservative or operative treatment possibilities, this study focused on patients with degenerative cartilage diseases.

METHODS

Thirty-two patients with chronic knee pain, a minimum age of 40 years, a negative history of trauma, and at least grade II degenerative cartilage disease were included. Cartilage abnormalities detected at preoperative 3-Tesla MRI (axial/koronar/sagittal PD-TSE-SPAIR, axial/sagittal 3D-T1-FFE, axial T2-FFE; Intera 3.0T, Philips Medical Systems) were classified (grades I-IV) and compared with arthroscopic findings.

RESULTS

Thirty-six percent (70/192) of the examined cartilage surfaces demonstrated no agreement between MRI and arthroscopic grading. In most of these cases, grades II and III cartilage lesions were confounded with each other. Regarding the positive predictive values, the probability that a positive finding in MRI would be exactly confirmed by arthroscopy was 39-72%. In contrast, specificities and negative predictive values of different grades of cartilage diseases were 85-95%.

CONCLUSIONS

Regarding the high specificities and negative predictive values, 3-Tesla MRI is a reliable method for excluding even slight cartilage degeneration. In summary, in degenerative cartilage diseases, 3-Tesla MRI is a supportive, noninvasive method for clinical decision making regarding conservative or operative treatment possibilities. However, the value of diagnostic arthroscopy for a definitive assessment of the articular surfaces and for therapeutic planning currently cannot be replaced by 3-Tesla MRI. This applies especially to treatment options in which a differentiation between grade II and III cartilage lesions is of interest.

Cartilage imaging at 3.0T with gradient refocused acquisition in the steady-state (GRASS) and IDEAL fat-water separation

PURPOSE

To demonstrate the feasibility of evaluating the articular cartilage of the knee joint at 3.0T using gradient refocused acquisition in the steady-state (GRASS) and iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) fat-water separation.

MATERIALS AND METHODS

Bloch equation simulations and a clinical pilot study (n = 10 knees) were performed to determine the influence of flip angle of the IDEAL-GRASS sequence on the signal-to-noise ratio (SNR) of cartilage and synovial fluid and the contrast-to-noise ratio (CNR) between cartilage and synovial fluid at 3.0T. The optimized IDEAL-GRASS sequence was then performed on 30 symptomatic patients as part of the routine 3.0T knee MRI examination at our institution.

RESULTS

The optimal flip angle was 50 degrees for IDEAL-GRASS cartilage imaging, which maximized contrast between cartilage and synovial fluid. The IDEAL-GRASS sequence consistently produced high-quality fat- and water-separated images of the knee with bright synovial fluid and 0.39 x 0.67 x 1.0 mm resolution in 5 minutes. IDEAL-GRASS images had high cartilage SNR and high contrast between cartilage and adjacent joint structures. The IDEAL-GRASS sequence provided excellent visualization of cartilage lesions in all patients.

CONCLUSION

The IDEAL-GRASS sequence shows promise for use as a morphologic cartilage imaging sequence at 3.0T.

Pelvic imaging using a T1W fat-suppressed three-dimensional dual echo Dixon technique at 3T

PURPOSE

To compare two T1-weighted (T1W) fat-suppressed sequences for 3D breath-hold pre- and postcontrast fat-suppressed T1W imaging of the female pelvis at 3T.

MATERIALS AND METHODS

Pelvic MRI scans of 16 female patients were retrospectively identified who were scanned with two 3D breath-hold sequences: 1) a fast spoiled gradient echo sequence with spectral inversion at lipids (SPECIAL) (called 3D FSPGR), and 2) a dual-echo two-point Dixon (DE Dixon) sequence. Contrast between soft tissue and fat, soft tissue and fluid, and fat and fluid was measured on pre- and postcontrast images. Additionally, two readers subjectively scored the images for degree and homogeneity of fat suppression plus presence and severity of artifacts.

RESULTS

Contrast between muscle and myometrium to fat was improved with the Dixon technique (0.61 vs. 0.09 and 0.7 vs. 0.3, respectively, P < 0.001). Both readers agreed that fat suppression was stronger with the Dixon sequence (P < 0.001 and P = 0.06). Artifacts were equivalent (P = 0.53 and 0.65).

CONCLUSION

The 3D DE Dixon sequence achieved stronger fat suppression in the female pelvis when compared to a 3D FSPGR sequence with SPECIAL.

Novel contrast mechanisms at 3 Tesla and 7 Tesla

Osteoarthritis (OA) is the most common musculoskeletal degenerative disease, affecting millions of people. Although OA has been considered primarily a cartilage disorder associated with focal cartilage degeneration, it is accompanied by well-known changes in subchondral and trabecular bone, including sclerosis and osteophyte formation. The exact cause of OA initiation and progression remains under debate, but OA typically first affects weightbearing joints such as the knee. Magnetic resonance imaging (MRI) has been recognized as a potential tool for quantitative assessment of cartilage abnormalities due to its excellent soft tissue contrast. Over the last two decades, several new MR biochemical imaging methods have been developed to characterize the disease process and possibly predict the progression of knee OA. These new MR biochemical methods play an important role not only for diagnosis of disease at an early stage, but also for their potential use in monitoring outcome of various drug therapies (success or failure). Recent advances in multicoil radiofrequency technology and high field systems (3 T and above) significantly improve the sensitivity and specificity of imaging studies for the diagnosis of musculoskeletal disorders. The current state-of-the-art MR imaging methods are briefly reviewed for the quantitative biochemical and functional imaging assessment of musculoskeletal systems.

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.

Reduction of truncation artifacts in rapid 3D articular cartilage imaging

PURPOSE

To reduce Gibbs ringing artifact in three-dimensional (3D) articular knee cartilage imaging with linear prediction (LP).

MATERIALS AND METHODS

A reconstruction method using LP in 3D was applied to truncated data sets of six healthy knees. The technique first linearizes the data before applying the prediction algorithm. Three radiologists blindly reviewed and ranked images of the full, truncated, and predicted data sets. Statistical analysis of the radiologists' reviews was performed for image quality, clinical acceptability of the images, and equivalence with the gold standard.

RESULTS

LP applied to 3D knee cartilage imaging allows for 40% decreased scan time while providing image quality with statistical equivalence to a full data set.

CONCLUSION

3D spoiled gradient echo imaging (SPGR) knee cartilage imaging requires significant scan time. This 40% reduction in scan time will allow such scans to be more feasible without sacrificing clinical acceptability.

Comparison of image quality in magnetic resonance imaging of the knee at 1.5 and 3.0 Tesla using 32-channel receiver coils

We examined to what degree the visualization of anatomic structures in the human knee is improved using 3.0-T magnetic resonance imaging (MRI) and many element RF receive coils as compared to 1.5 T. We imaged 20 knees at 1.5 and 3.0 T using T2-weighted STIR, T2-weighted gradient echo, T1-weighted spin-echo, true-FISP and T2-weighted fast spin echo techniques in conjunction with 32-element RF coil arrays. The 3.0-T examination was considerably faster than its 1.5-T counterpart. A superior subjective visibility at 3.0 T vs 1.5 T was found in 27 of 50 evaluated structures (meniscus, ligaments) with the exception of true-FISP techniques. The 3.0-T examination provided a better visibility (evaluated by blinded consensus-reading by two radiologists) of small structures such as the ligamentum transversum genu. Also, cartilage was better delineated at 3.0 T. A 23% increased average signal-to-noise ratio as assessed using a temporal filter was observed at 3.0 T as compared to 1.5 T. At 3.0 T, imaging of the human knee is faster and results in a subjective visibility of anatomic structures that is superior to and competitive with 1.5 T.

Internal knee derangement assessed with 3-minute three-dimensional isovoxel true FISP MR sequence: preliminary study

PURPOSE

To prospectively evaluate the accuracy of magnetic resonance (MR) imaging of the knee performed by using a three-dimensional (3D) isovoxel sequence involving an acquisition time of approximately 3 minutes, with surgery as the reference standard.

MATERIALS AND METHODS

The study was institutional review board approved. Written informed consent was obtained from all patients. Thirty knees of 29 patients (14 women, 15 men; mean age, 41 years) were prospectively examined by using a 3D isovoxel true fast imaging with steady-state precession (FISP) sequence with water excitation and secondary multiplanar reformations. All patients underwent arthroscopy within 12 days after true FISP MR imaging. Two blinded readers evaluated the MR images. Accuracy for detection of cartilage defects and anterior cruciate ligament (ACL) and meniscal tears, interobserver agreement, and intermethod agreement were calculated.

RESULTS

Overall sensitivity, specificity, and accuracy of isovoxel true FISP imaging for the diagnosis of cartilage defects were 45%, 83%, and 76%, respectively, for reader 1 and 63%, 82%, and 83%, respectively, for reader 2. Averaged (for readers 1 and 2) sensitivity, specificity, and accuracy of isovoxel true FISP imaging were, respectively, 80%, 95%, and 90% for diagnosis of ACL tear; 100%, 82%, and 90% for diagnosis of medial meniscal tear; and 83%, 83%, and 83% for diagnosis of lateral meniscal tear. The standard MR sequences used at the authors' institution had overall sensitivities, specificities, and accuracies of 39%, 83%, and 71%, respectively, for reader 1 and 37%, 85%, and 76%, respectively, for reader 2. Averaged sensitivity, specificity, and accuracy of the standard MR sequences were, respectively, 70%, 100%, and 90% for diagnosis of ACL tear; 96%, 77%, and 85% for diagnosis of medial meniscal tear; and 83%, 77%, and 78% for diagnosis of lateral meniscal tear.

CONCLUSION

The diagnostic performance of knee MR imaging performed by using a 3D water excitation isovoxel true FISP sequence and an imaging time of approximately 3 minutes is comparable to the diagnostic performance of the MR sequences used as standards at the authors' institution.

Cartilage thickness: factors influencing multidetector CT measurements in a phantom study

PURPOSE

To prospectively assess in a phantom the reconstruction errors and detection limits of cartilage thickness measurements obtained with multidetector computed tomographic (CT) arthrography, as a function of contrast agent concentration, scanning direction, spatial resolution, joint spacing, and tube current, with known measurements as the reference standard.

MATERIALS AND METHODS

A phantom with nine chambers was constructed. Each chamber had a nylon cylinder encased by sleeves of aluminum and polycarbonate to simulate trabecular bone, cortical bone, and cartilage. Varying simulated cartilage thicknesses and 10 joint space widths were assessed. On 3 days, the phantom was scanned with and without contrast agent administration and with the chamber axes both perpendicular and parallel to the scanner axis. Images were reconstructed at 1.0- and 0.5-mm intervals. Contrast agent concentration and tube current were varied. The simulated cartilage thickness was determined by using image segmentation. Root mean squared errors and mean residual errors were used to characterize the measurements. The reproducibility of the CT scanner and image segmentation results was determined.

RESULTS

Simulated cartilage greater than 1.0 mm in thickness was reconstructed with less than 10% error when either no contrast agent or a low concentration (25%) of contrast agent was used. Error increased as contrast agent concentration increased. Decreasing the simulated joint space width to 0.5 mm caused slight increases in error; however, error increased substantially at joint spaces narrower than 0.5 mm. Errors in measurements derived from anisotropic CT data were greater than errors in measurements derived from isotropic data. Altering the tube current did not substantially affect reconstruction errors.

CONCLUSION

The study revealed lower boundaries and the repeatability of simulated cartilage thickness measurements obtained by using multidetector CT arthrography and yielded data pertinent to choosing the contrast agent concentration, joint space width, scanning direction, and spatial resolution to reduce reconstruction errors.

Imaging of knee osteoarthritis: data beyond the beauty

PURPOSE OF REVIEW

MRI has revolutionized osteoarthritis research by providing semi-quantitative and quantitative imaging endpoints on most articular tissues. With the first image data of the Osteoarthritis Initiative now becoming publicly available, this article reviews recent developments in quantitative imaging of osteoarthritis.

RECENT FINDINGS

Although radiography remains the standard for regulatory studies on disease modifying osteoarthritis drugs, there is no consensus on the optimal positioning and acquisition protocol. With MRI, semi-quantitative scoring systems for evaluation of multiple articular tissue changes have been developed and are currently investigated in the context of correlation with symptoms and of predicting structural progression of osteoarthritis. Most efforts on quantitative measurement of imaging endpoints have focused on cartilage morphology and composition, with higher field strength (3T), newer sequences, and new measurement endpoints being a driver of current innovation.

SUMMARY

The semi-quantitative and quantitative tools for analysis of articular structure are now available and permit comprehensive analysis of morphological and compositional tissue changes in osteoarthritis. These changes will need to be related to clinical outcomes (e.g. how a patient feels or functions) with current epidemiological studies, such as the Osteoarthritis Initiatives, providing the opportunity for clinical validation of these imaging biomarkers.