Magnetic resonance imaging of knee cartilage using a water selective balanced steady-state free precession sequence

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.

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.

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.

Spectrally selective imaging with wideband balanced steady-state free precession MRI

PURPOSE

Unwanted, bright fat signals in balanced steady-state free precession sequences are commonly suppressed using spectral shaping. Here, a new spectral-shaping method is proposed to significantly improve the uniformity of stopband suppression without compromising the level of passband signals.

METHODS

The proposed method combines binomial-pattern excitation pulses with a wideband balanced steady-state free precession sequence kernel. It thereby increases the frequency separation between the centers of pass and stopbands by π radians, enabling improved water-fat contrast. Simulations were performed to find the optimal flip angles and subpulse spacing for the binomial pulses that maximize contrast and signal efficiency.

RESULTS

Comparisons with a conventional binomial balanced steady-state free precession sequence were performed in simulations as well as phantom and in vivo experiments at 1.5 T and 3 T. Enhanced fat suppression is demonstrated in vivo with an average improvement of 58% in blood-fat and 68% in muscle-fat contrast (P < 0.001, Wilcoxon signed-rank test).

CONCLUSION

The proposed binomial wideband balanced steady-state free precession method is a promising candidate for spectrally selective imaging with enhanced reliability against field inhomogeneities.

Sequence design and evaluation of the reproducibility of water-selective diffusion-weighted imaging of the breast at 3 T

Diffusion measurements derived from breast MRI can be adversely affected by unwanted signals from abundant fatty tissues if they are not suppressed adequately. To minimize this undesired contribution, we designed and optimized a water-selective diffusion-weighted imaging (DWI) sequence, which relies on spectrally selective excitation on the water resonance, obviating the need for fat suppression. As this method is more complex than standard DWI methods, we also report a test-retest study to evaluate its reproducibility. In this study, a spectrally selective Gaussian pulse on water resonance was combined with a pair of slice-selective adiabatic refocusing pulses for water-only DWI. Field map-based shimming and manual determination of the center frequency were used for water selection. The selectivity of the excitation pulse was optimized by a spectrally selective spectroscopy sequence based on the same principles. A test-retest study of 10 volunteers in two separate visits was used to evaluate its reproducibility. Our results from all subjects showed high-quality diffusion-weighted images of the breast without fat contamination. Mean apparent diffusion coefficients for b = 0, 600 s/mm(2) and b = 50, 600 s/mm(2) all showed good reproducibility, as 95% confidence intervals of the apparent diffusion coefficients were 4 × 10(-5)  mm(2) /s and 5 × 10(-5)  mm(2) /s and repeatability values were 1.09 × 10(-4) and 1.31 × 10(-4) , respectively. In conclusion, water-selective DWI is a feasible alternative to standard methods of DWI based on fat suppression. The added complexity of the method does not compromise the reproducibility of diffusion measurements in the breast.

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.

Qualitative and quantitative assessment of wrist MRI at 3.0T: comparison between isotropic 3D turbo spin echo and isotropic 3D fast field echo and 2D turbo spin echo

BACKGROUND

Isotropic three-dimensional (3D) magnetic resonance imaging (MRI) has been applied to various joints. However, comparison for image quality between isotropic 3D MRI and two-dimensional (2D) turbo spin echo (TSE) sequence of the wrist at a 3T MR system has not been investigated.

PURPOSE

To compare the image quality of isotropic 3D MRI including TSE intermediate-weighted (VISTA) sequence and fast field echo (FFE) sequence with 2D TSE intermediate-weighted sequence of the wrist joint at 3.0 T.

MATERIAL AND METHODS

MRI was performed in 10 wrists of 10 healthy volunteers with isotropic 3D sequences (VISTA and FFE) and 2D TSE intermediate-weighted sequences at 3.0 T. The signal-to-noise ratio (SNR) was obtained by imaging phantom and noise-only image. Contrast ratios (CRs) were calculated between fluid and cartilage, triangular fibrocartilage complex (TFCC), and the scapholunate ligament. Two radiologists independently assessed the visibility of TFCC, carpal ligaments, cartilage, tendons and nerves with a four-point grading scale. Statistical analysis to compare CRs (one way ANOVA with a Tukey test) and grades of visibility (Kruskal-Wallis test) between three sequences and those for inter-observer agreement (kappa analysis) were performed.

RESULTS

The SNR of 2D TSE (46.26) was higher than those of VISTA (23.34) and 3D FFE (19.41). CRs were superior in 2D TSE than VISTA (P = 0.02) for fluid-cartilage and in 2D TSE than 3D FFE (P < 0.01) for fluid-TFCC. The visibility was best in 2D TSE (P < 0.01) for TFCC and in VISTA (P = 0.01) for scapholunate ligament. The visibility was better in 2D TSE and 3D FFE (P = 0.04) for cartilage and in VISTA than 3D FFE (P < 0.01) for TFCC. The inter-observer agreement for the visibility of anatomic structures was moderate or substantial.

CONCLUSION

Image quality of 2D TSE was superior to isotropic 3D MR imaging for cartilage, and TFCC. 3D FFE has better visibility for cartilage than VISTA and VISTA has superior visibility for TFCC to 3D FFE and the visibility for scapholunate ligament was best on VISTA.

ISMRM workshop on fat-water separation: insights, applications and progress in MRI

Approximately 130 attendees convened on February 19-22, 2012 for the first ISMRM-sponsored workshop on water-fat imaging. The motivation to host this meeting was driven by the increasing number of research publications on this topic over the past decade. The scientific program included an historical perspective and a discussion of the clinical relevance of water-fat MRI, a technical description of multiecho pulse sequences, a review of data acquisition and reconstruction algorithms, a summary of the confounding factors that influence quantitative fat measurements and the importance of MRI-based biomarkers, a description of applications in the heart, liver, pancreas, abdomen, spine, pelvis, and muscles, an overview of the implications of fat in diabetes and obesity, a discussion on MR spectroscopy, a review of childhood obesity, the efficacy of lifestyle interventional studies, and the role of brown adipose tissue, and an outlook on federal funding opportunities from the National Institutes of Health.

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.

Evaluation of the chondromalacia patella using a microscopy coil: comparison of the two-dimensional fast spin echo techniques and the three-dimensional fast field echo techniques

OBJECTIVE

We wanted to compare the two-dimensional (2D) fast spin echo (FSE) techniques and the three-dimensional (3D) fast field echo techniques for the evaluation of the chondromalacia patella using a microscopy coil.

MATERIALS AND METHODS

Twenty five patients who underwent total knee arthroplasty were included in this study. Preoperative MRI evaluation of the patella was performed using a microscopy coil (47 mm). The proton density-weighted fast spin echo images (PD), the fat-suppressed PD images (FS-PD), the intermediate weighted-fat suppressed fast spin echo images (iw-FS-FSE), the 3D balanced-fast field echo images (B-FFE), the 3D water selective cartilage scan (WATS-c) and the 3D water selective fluid scan (WATS-f) were obtained on a 1.5T MRI scanner. The patellar cartilage was evaluated in nine areas: the superior, middle and the inferior portions that were subdivided into the medial, central and lateral facets in a total of 215 areas. Employing the Noyes grading system, the MRI grade 0-I, II and III lesions were compared using the gross and microscopic findings. The sensitivity, specificity and accuracy were evaluated for each sequence. The significance of the differences for the individual sequences was calculated using the McNemar test.

RESULTS

The gross and microscopic findings demonstrated 167 grade 0-I lesions, 40 grade II lesions and eight grade III lesions. Iw-FS-FSE had the highest accuracy (sensitivity/specificity/accuracy = 88%/98%/96%), followed by FS-PD (78%/98%/93%, respectively), PD (76%/98%/93%, respectively), B-FFE (71%/100%/93%, respectively), WATS-c (67%/100%/92%, respectively) and WATS-f (58%/99%/89%, respectively). There were statistically significant differences for the iw-FS-FSE and WATS-f and for the PD-FS and WATS-f (p < 0.01).

CONCLUSION

The iw-FS-FSE images obtained with a microscopy coil show best diagnostic performance among the 2D and 3D GRE images for evaluating the chondromalacia patella.

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.

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.

Dual half-echo phase correction for implementation of 3D radial SSFP at 3.0 T

Fat/water separation methods such as fluctuating equilibrium magnetic resonance and linear combination steady-state free precession have not yet been successfully implemented at 3.0 T due to extreme limitations on the time available for spatial encoding with the increase in magnetic field strength. We present a method to utilize a three-dimensional radial sequence combined with linear combination steady-state free precession at 3.0 T to take advantage of the increased signal levels over 1.5 T and demonstrate high spatial resolution compared to Cartesian techniques. We exploit information from the two half-echoes within each pulse repetition time to correct the accumulated phase on a point-by-point basis, thereby fully aligning the phase of both half-echoes. The correction provides reduced sensitivity to static field (B(0)) inhomogeneity and robust fat/water separation. Resultant images in the knee joint demonstrate the necessity of such a correction, as well as the increased isotropic spatial resolution attainable at 3.0 T. Results of a clinical study comparing this sequence to conventional joint imaging sequences are included.

Overuse injuries of the knee

Overuse injuries are a common cause of morbidity in athletes. They occur after repetitive microtrauma, abnormal joint alignment, and poor training technique without appropriate time to heal. Overuse injuries are frequent in the knee joint because of the numerous attachment sites for lower limb musculature and tendons surrounding the joint. MR imaging is regarded as the noninvasive technique of choice for detection of internal derangements of the knee. This article describes the characteristic findings on MR of the common overuse injuries in the knee, including patellar tendinopathy, iliotibial band syndrome, cartilage disorders, medial plica syndrome, and bursitis.

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.

Prospective comparison of 3D FIESTA versus fat-suppressed 3D SPGR MRI in evaluating knee cartilage lesions

AIM

To prospectively compare the accuracy of three-dimensional fast imaging employing steady-state acquisition (3D FIESTA) sequences with that of fat-suppressed three-dimensional spoiled gradient-recalled (3D SPGR) in the diagnosis of knee articular cartilage lesions, using arthroscopy as the reference standard.

MATERIALS AND METHODS

Fifty-eight knees in 54 patients (age range 21-82 years; mean 36 years) were prospectively evaluated by using sagittal 3D FIESTA and sagittal fat-suppressed 3D SPGR sequences. Articular cartilage lesions were graded on MRI and during arthroscopy with a modified Noyes scoring system. Sensitivity, specificity, and accuracy were assessed. Interobserver agreement was determined with kappa statistics.

RESULTS

The performance of 3D FIESTA sequences (sensitivity, specificity, and accuracy were 80, 94, and 92%, respectively, for reader 1 and 76, 94, and 90%, respectively, for reader 2) was similar to that of fat-suppressed 3D SPGR sequences (sensitivity, specificity, and accuracy were 82, 92, and 90%, respectively, for reader 1 and 82, 90, and 88%, respectively, for reader 2) in the detection of knee articular cartilage lesions. The interobserver agreement varied from fair to good to excellent (kappa values from 0.43-0.83).

CONCLUSION

3D FIESTA has good diagnostic performance, comparable with fat-suppressed 3D SPGR in evaluating knee cartilage lesions, and it can be incorporated into routine knee MRI protocols due to the short acquisition time.

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.

Articular Cartilage Defects Detected with 3D Water-Excitation True FISP: Prospective Comparison with Sequences Commonly Used for Knee Imaging

PURPOSE

To prospectively compare the accuracy of three-dimensional (3D) water-excitation (WE) true fast imaging with steady-state precession (FISP) in the diagnosis of articular cartilage defects with that of sequences commonly used to image the knee, with arthroscopy or surgery as the reference standard.

MATERIALS AND METHODS

This study protocol was institutional review board approved. Written informed consent was obtained from all patients. Thirty knees in 29 patients (mean age, 56 years; range, 18-86 years) were prospectively evaluated by using sagittal 3D WE true FISP with two section thicknesses (1.7 mm [true FISPthin] and 3.0 mm [true FISPthick]), two-dimensional (2D) intermediate-weighted spin-echo with fat saturation, 2D fast short inversion time inversion-recovery, 3D WE double-echo steady-state, and 3D fat-saturated fast low-angle shot sequences. Cartilage defects were graded on magnetic resonance images and during surgery with a modified Noyes scoring system. Contrast-to-noise ratio (CNR) and CNR efficiency were calculated. Sensitivity, specificity, and accuracy were assessed. Interobserver agreement was determined with kappa statistics, and quantitative results were evaluated with the Wilcoxon signed rank test.

RESULTS

The performance of 3D WE true FISPthick (sensitivity, specificity, and accuracy, respectively, were 52%, 93%, and 71% for reader 1 and 65%, 88%, and 76% for reader 2) and 3D WE true FISPthin (sensitivity, specificity, and accuracy, respectively, were 58%, 94%, and 75% for reader 1 and 63%, 80%, and 71% for reader 2) sequences was no different than that of other sequences in the detection of circumscribed defects. Three-dimensional WE true FISP sequences had a significantly (P<.0033) higher CNR and CNR efficiency between cartilage and fluid than the corresponding sequences with the same section thickness.

CONCLUSION

Three-dimensional WE true FISP enables high contrast between joint fluid and articular cartilage and a diagnostic performance that is comparable with that of standard sequences.

Isotropic MRI of the knee with 3D fast spin-echo extended echo-train acquisition (XETA): initial experience

OBJECTIVE

The purpose of our study was to prospectively compare a recently developed method of isotropic 3D fast spin-echo (FSE) with extended echo-train acquisition (XETA) with 2D FSE and 2D fast recovery FSE (FRFSE) for MRI of the knee.

SUBJECTS AND METHODS

Institutional review board approval, Health Insurance Portability and Accounting Act (HIPAA) compliance, and informed consent were obtained. We studied 10 healthy volunteers and one volunteer with knee pain using 3D FSE XETA, 2D FSE, and 2D FRFSE. Images were obtained both with and without fat suppression. Cartilage and muscle signal-to-noise ratio (SNR) and cartilage-fluid contrast-to-noise ratio (CNR) were compared using a Student's t test. We also compared reformations of 3D FSE XETA with 2D FSE images directly acquired in the axial plane.

RESULTS

Cartilage SNR was higher with 3D FSE XETA (56.8 +/- 9 [SD]) compared with the 2D FSE (45.8 +/- 8, p < 0.01) and 2D FRFSE (32.5 +/- 5.3, p < 0.01). Muscle SNR was significantly higher with 3D FSE XETA (52.1 +/- 4.3) than 2D FSE (45.2 +/- 9, p < 0.01) and 2D FRFSE (23.6 +/- 6.2, p < 0.01). Fluid SNR was significantly higher for 2D FSE (144.9 +/- 33) than 3D FSE XETA (104.7 +/- 18, p < 0.01). Compared with 2D FSE and 2D FRFSE, 3D FSE XETA had lower cartilage-fluid CNR due to higher cartilage SNR (p < 0.01). Three-dimensional FSE XETA acquired volumetric data sets with isotropic resolution. Reformatted images in the axial plane were similar to axial 2D FSE acquisitions but with thinner slices.

CONCLUSION

Three-dimensional FSE XETA acquires high-resolution (approximately 0.7 mm) isotropic data with intermediate and T2-weighting that may be reformatted in arbitrary planes. Three-dimensional FSE XETA is a promising technique for MRI of the knee.

Balanced SSFP imaging of the musculoskeletal system

Magnetic resonance imaging (MRI), with its unique ability to image and characterize soft tissue noninvasively, has emerged as one of the most accurate imaging methods available to diagnose bone and joint pathology. Currently, most evaluation of musculoskeletal pathology is done with two-dimensional acquisition techniques such as fast spin echo (FSE) imaging. The development of three-dimensional fast imaging methods based on balanced steady-state free precession (SSFP) shows great promise to improve MRI of the musculoskeletal system. These methods may allow acquisition of fluid sensitive isotropic data that can be reformatted into arbitrary planes for improved detection and visualization of pathology. Sensitivity to fluid and fat suppression are important issues in these techniques to improve delineation of cartilage contours, for detection of marrow edema and derangement of other joint structures.

Evaluation of ganglion cysts using vastly undersampled isotropic projection reconstruction (VIPR)

For some atypical para-articular ganglia, the presence of a joint connection is highly controversial. The proper preoperative diagnosis and identification of this joint connection for ganglion cysts is important for patient treatment and outcome. MRI is the imaging modality of choice when evaluating such lesions, but the detection of subtle joint connections remains difficult with conventional MR protocols. We investigated the utility of a steady-state free-precession acquisition with isotropic high resolution using the vastly undersampled isotropic projection reconstruction (VIPR) pulse sequence to determine if joint connections for ganglion cysts could be seen more effectively, using the knee region as a model. We evaluated four patients: two with peroneal intraneural ganglion cysts, one with adventitial cystic disease of the popliteal artery, and one patient with a more typical extraneural (intramuscular) cyst. Both conventional MR and VIPR techniques were used. In our clinical experience, we found VIPR to be superior to conventional MR techniques in detecting and depicting joint connections in typical and atypical ganglion cysts around the knee.

Volumetric cartilage measurements of porcine knee at 1.5-T and 3.0-T MR imaging: evaluation of precision and accuracy

PURPOSE

To compare the precision and accuracy of 3.0-T and 1.5-T magnetic resonance (MR) imaging in the quantification of cartilage volume by using direct volumetric measurements as a reference standard.

MATERIALS AND METHODS

The local animal experimentation committee did not require its approval for this study. Porcine knees were obtained from an abattoir. These specimens were used to optimize imaging parameters regarding effective signal-to-noise ratio (SNRE) and contrast-to-noise ratio (CNRE) for a fat-saturated spoiled gradient-recalled acquisition in the steady state (SPGR) sequence, a water excitation SPGR sequence, and a fast spin-echo sequence at 3.0 T and a fat-saturated SPGR sequence at 1.5 T. By using the optimized sequences, 18 specimens were imaged in less than 6 minutes per sequence. A fivefold repetition of measurements of four specimens was performed for precision analysis. Cartilage was segmented by using semiautomatic software to calculate the volume. After imaging, the cartilage was scraped off and the volume was measured directly by using a saline-displacement method to calculate accuracy. Precision and accuracy errors were calculated as the root-mean-squares of the single errors per specimen.

RESULTS

SNRE and CNRE values, respectively, were highest for the water excitation sequence at 3.0 T (1.81 sec(-1/2) and 1.27 sec(-1/2)), followed by the fat-saturated SPGR sequence (1.52 sec(-1/2) and 1.07 sec(-1/2)). The fast spin-echo sequence and the fat-saturated SPGR sequence at 1.5 T had lower SNR(E) (1.27 sec(-1/2) and 0.59 sec(-1/2), respectively). Accuracy error for MR-based volume calculation at the femur was 5.0%, 3.0%, 21%, and 16% for the water excitation, fat-saturated SPGR, and fast spin-echo sequences at 3.0 T and the fat-saturated SPGR sequence at 1.5 T, respectively.

CONCLUSION

MR imaging at 3.0 T was shown in our study to better quantify cartilage volume. SNRE and CNRE were substantially improved, resulting in significantly higher accuracy in determining cartilage volume.

Advanced magnetic resonance imaging of articular cartilage

MRI is one of the most accurate imaging methods available to diagnose disorders of articular cartilage. Conventional two-dimensional and three-dimensional approaches show changes in cartilage morphology. Newer and substantially faster three-dimensional imaging methods show great promise to improve MRI of cartilage. These methods may allow acquisition of fluid-sensitive isotropic data that can be reformatted into arbitrary planes for improved detection and visualization of pathology. Unique MRI contrast mechanisms also allow clinicians to probe cartilage physiology and detect early changes in cartilage macromolecules.

Osteoarthritis of the knee: association between clinical features and MR imaging findings

PURPOSE

To prospectively evaluate the association between clinical features and structural abnormalities found at magnetic resonance (MR) imaging in patients with osteoarthritis (OA) of the knee.

MATERIALS AND METHODS

The study was approved by the institutional medical ethics review board. Written informed consent was obtained from each patient. MR images of the knee were obtained from 205 (42 [20%] men, 163 [80%] women; median age, 60 years; range, 43-77 years) patients in whom symptomatic OA at multiple joint sites was diagnosed. MR images were analyzed for various abnormalities of OA. All patients were interviewed concerning pain and stiffness in the knee that was imaged. Odds ratios (ORs) with 99% confidence intervals (CIs) were used to determine the association between the imaging findings and clinical features of OA.

RESULTS

A large joint effusion was associated with pain (OR, 9.99; 99% CI: 1.28, 149) and stiffness (OR, 4.67; 99% CI: 1.26, 26.1). The presence of an osteophyte in the patellofemoral compartment (OR, 2.25; 99% CI: 1.06, 4.77) was associated with pain. All other imaging findings, including focal or diffuse cartilaginous abnormalities, subchondral cysts, bone marrow edema, subluxation of the meniscus, meniscal tears, or Baker cysts, were not associated with symptoms.

CONCLUSION

Findings of this study indicate that only two associations exist between clinical symptoms and structural findings found on MR images in patients with OA of the knee.

MRI of articular cartilage in OA: novel pulse sequences and compositional/functional markers

Osteoarthritis (OA) is a leading cause of disability worldwide. Magnetic resonance imaging (MRI), with its unique ability to image and characterize soft tissue non-invasively, has proven valuable in assessing cartilage in OA. The development of new, fast imaging methods with high contrast show promise to improve the magnetic resonance (MR) evaluation of this disease. In addition to morphologic MRI methods, MRI contrast mechanisms under development may reveal detailed information about the physiology of cartilage. It is anticipated that these and other MRI techniques will play an increasingly important role in assessing the success or failure of therapies for OA. On December 5 and 6, 2002, OMERACT (Outcome Measures in Rheumatology Clinical Trials) and OARSI (Osteoarthritis Research Society International) held a workshop in Bethesda, MD aiming at providing a state-of-the-art review of imaging outcome measures for OA of the knee to help guide scientists and pharmaceutical companies in the use of MRI in multi-site studies of OA. Applications of MRI were initially reviewed by a multidisciplinary, international panel of expert scientists and physicians from academia, the pharmaceutical industry and regulatory agencies. The findings of the panel were then presented to a wider group of participants for open discussion. The following report summarizes the results of these discussions with respect to novel MRI pulse sequences for evaluating articular cartilage of the knee in OA and notes any additional advances that have been made since.

Magnetic resonance imaging of articular cartilage: trauma, degeneration, and repair

The assessment of articular cartilage using magnetic resonance imaging has seen considerable advances in recent years. Cartilage morphologic characteristics can now be evaluated with a high degree of accuracy and reproducibility using dedicated pulse sequences, which are becoming standard at many institutions. These techniques detect clinically unsuspected traumatic cartilage lesions, allowing the physician to study their natural history with longitudinal evaluation and also to assess disease status in degenerative osteoarthritis. Magnetic resonance imaging also provides a more objective assessment of cartilage repair to augment the information obtained from more subjective clinical outcome instruments. Newly developed methods that provide detail at an ultrastructural level offer an important addition to cartilage evaluation, particularly in the detection of early alterations in the extracellular matrix. These methods have created an undeniably important role for magnetic resonance imaging in the reproducible, noninvasive, and objective evaluation and monitoring of cartilage. An overview of the advances, current techniques, and impact of magnetic resonance imaging in the setting of trauma, degenerative arthritides, and surgical treatment for cartilage injury is presented.

Quantitative Assessment of Patellar Cartilage Volume and Thickness at 3.0 Tesla Comparing a 3D-Fast Low Angle Shot Versus a 3D-True Fast Imaging With Steady-State Precession Sequence for Reproducibility

OBJECTIVES

We sought to compare patellar cartilage volume and thickness measurement between 3D-FLASH and 3D-True fast imaging with steady-state precession (FISP) image data at 3.0 T.

MATERIALS AND METHODS

One knee each of 6 healthy adults was examined by axial magnetic resonance imaging (MRI) performed with a 3D-fast flow angle shot (FLASH) water-excitation sequence and a 3D-TrueFISP water-excitation sequence (spatial resolution 0.31 x 0.31 x 1.5 mm3). Patellar cartilage volume and mean/maximum thickness were calculated. Intraindividual/average reproducibility and interindividual variability were determined from 3 consecutive data sets acquired for each volunteer and sequence.

RESULTS

Patellar cartilage volume and thickness as well as reproducibility was slightly but not significantly lower for the 3D-TrueFISP data than for the 3D-FLASH data (volume: 3.4-6.3 mL (3D-FLASH)/3.1-6.0 mL (3D-TrueFISP), average reproducibility 1.8% (3D-FLASH)/4.4% (3D-TrueFISP); mean thickness: 2.1-2.8 mm (3D-FLASH)/1.9-2.6 mm (3D-TrueFISP), average reproducibility 2.8% (3D-FLASH)/3.8% (3D-TrueFISP); maximum thickness: 4.7-6.6 mm (3D-FLASH)/4.5-6.2 mm (3D-TrueFISP), average reproducibility 2.6% (3D-FLASH)/4.1% (3D-TrueFISP)). Interindividual variability was comparable for both sequence techniques.

CONCLUSION

At 3.0 T, the 3D-FLASH sequence showed tendency to be slightly superior to the 3D-TrueFISP sequence considering robust and valid assessment of quantitative cartilage parameters in young healthy adults, although there was found no significant statistical difference between both imaging techniques. However, in patients suffering from osteoarthritis (OA), the 3D-TrueFISP sequence might prove advantageous for monitoring of disease progression and evaluation of therapy success, particularly because the substantially higher signal to noise ratio/contrast to noise ratio values might allow for higher spatial resolution and hence for improvement of the accuracy of segmentation process especially at the articular surface.

Evaluation of the articular cartilage of the knee joint with vastly undersampled isotropic projection reconstruction steady-state free precession imaging

PURPOSE

To determine the feasibility of the vastly undersampled isotropic projection reconstruction steady-state free precession (VIPR-SSFP) sequence for evaluating the articular cartilage of the knee joint.

MATERIALS AND METHODS

A magnetic resonance (MR) examination of the knee was performed on 33 subjects using a GE 1.5T scanner and a phased-array extremity coil. VIPR-SSFP, proton density-weighted fast spin-echo (PD-FSE), fat-suppressed T2-weighted fast spin-echo (T2-FSE), and three-dimensional fat-suppressed spoiled gradient recall-echo (SPGR) sequences were performed on three asymptomatic volunteers and 10 patients with osteoarthritis of the knee joint. Signal-to-noise efficiency, and contrast-to-noise ratio (CNR) measurements were calculated for all sequences and compared with the use of paired t-tests. The VIPR-SSFP sequence was then performed on 20 consecutive patients who were undergoing a routine MR examination of the knee.

RESULTS

The cartilage signal-to-noise efficiency of the VIPR-SSFP sequence was not significantly different from that of the PD-FSE and SPGR sequences. The cartilage signal-to-noise efficiency of the VIPR-SSFP sequence was significantly higher (P < 0.05) than that of the T2-FSE sequence. The VIPR-SSFP sequence produced images with significantly higher (P < 0.05) CNR between cartilage and synovial fluid than the PD-FSE and SPGR sequences, and significantly higher (P < 0.05) CNR between cartilage and subchondral bone than the T2-FSE sequence. The VIPR-SSFP sequence allowed excellent visualization of the articular cartilage of the knee joint in all subjects. All articular cartilage defects identified on the PD-FSE, T2-FSE, and SPGR images were well visualized on the VIPR-SSFP images.

CONCLUSION

VIPR-SSFP images had high cartilage signal-to-noise efficiency and high CNR between cartilage and adjacent synovial fluid and subchondral bone; therefore, the sequence is well suited for evaluating the articular cartilage of the knee joint.

MR imaging of articular cartilage at 1.5T and 3.0T: comparison of SPGR and SSFP sequences

OBJECTIVE

To compare articular cartilage signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and thickness measurements on a 1.5 T and a 3.0 T magnetic resonance (MR) scanner using three-dimensional spoiled gradient recalled echo (3D-SPGR) and two 3D steady-state free precession (SSFP) sequences.

METHODS

Both knees of five volunteers were scanned at 1.5 T and at 3.0 T using a transmit-receive quadrature extremity coil. Each examination consisted of a sagittal 3D-SPGR sequence, a sagittal fat suppressed 3D-SSFP (FS-SSFP) sequence, and a sagittal Dixon 3D-SSFP sequence. For quantitative analysis, we compared cartilage SNR and CNR efficiencies, as well as average cartilage thickness measurements.

RESULTS

For 3D-SPGR, cartilage SNR efficiencies at 3.0 T increased compared to those at 1.5 T by a factor of 1.83 (range: 1.40-2.09). In comparison to 3D-SPGR, the SNR efficiency of FS-SSFP increased by a factor of 2.13 (range: 1.81-2.39) and for Dixon SSFP by a factor of 2.39 (range: 1.95-2.99). For 3D-SPGR, CNR efficiencies between cartilage and its surrounding tissue increased compared to those at 1.5 T by a factor of 2.12 (range: 1.75-2.47), for FS-SSFP by a factor 2.11 (range: 1.58-2.80) and for Dixon SSFP by a factor 2.39 (range 2.09-2.83). Average cartilage thicknesses of load bearing regions were not different at both field strengths or between sequences (P>0.05). Mean average cartilage thickness measured in all knees was 2.28 mm.

CONCLUSION

Articular cartilage imaging of the knee on a 3.0 T MR scanner shows increased SNR and CNR efficiencies compared to a 1.5 T scanner, where SSFP-based techniques show the highest increase in SNR and CNR efficiency. There was no difference between average cartilage thickness measurements performed at the 1.5 T and 3.0 T scanners or between the three different sequences.

The relationship between the MRI features of mild osteoarthritis in the patellofemoral and tibiofemoral compartments of the knee

The aim of this work was to demonstrate the relationship between osteoarthritic changes seen on magnetic resonance (MR) images of the patellofemoral (PF) or tibiofemoral (TF) compartments in patients with mild osteoarthritis (OA) of the knee. MR images of the knee were obtained in 105 sib pairs (210 patients) who had been diagnosed with OA at multiple joints. Entry criteria included that the degree of OA in the knee examined should be between a Kellgren and Lawrence score of 2 or 3. MR images were analyzed for the presence of cartilaginous lesions, bone marrow edema (BME) and meniscal tears. The relationship between findings in the medial and lateral aspects of the PF and TF compartments was examined. The number of cartilaginous defects on either side of the PF compartment correlated positively with number of cartilaginous defects in the ipsilateral TF compartment (odds ratio, OR, 55, confidence interval, CI, 7.8-382). The number of cartilaginous defects in the PF compartment correlated positively with ipsilateral meniscal tears (OR 3.7, CI 1.0-14) and ipsilateral PF BME (OR 17, CI 3.8-72). Cartilaginous defects in the TF compartment correlated positively with ipsilateral meniscal tears (OR 9.8, CI 2.5-38) and ipsilateral TF BME (OR 120, CI 6.5-2,221). Osteoarthritic defects lateralize or medialize in the PF and TF compartments of the knee in patients with mild OA.