Faculty Bibliography

PURPOSE/OBJECTIVE: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/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/CONCLUSIONS:The IDEAL-GRASS sequence shows promise for use as a morphologic cartilage imaging sequence at 3.0T.

Recent advances have reduced scan time in three-dimensional fast spin echo (3D-FSE) imaging, including very long echo trains through refocusing flip angle (FA) modulation and 2D-accelerated parallel imaging. This work describes a method to modulate refocusing FAs that produces sharp point spread functions (PSFs) from very long echo trains while exercising direct control over minimum, center-k-space, and maximum FAs in order to accommodate the presence of flow and motion, SNR requirements, and RF power limits. Additionally, a new method for ordering views to map signal modulation from the echo train into k(y)-k(z) space that enables nonrectangular k-space grids and autocalibrating 2D-accelerated parallel imaging is presented. With long echo trains and fewer echoes required to encode large matrices, large volumes with high in- and through-plane resolution matrices may be acquired with scan times of 3-6 min, as demonstrated for volumetric brain, knee, and kidney imaging.

OBJECTIVE:The objective was to evaluate magnetic resonance imaging (MRI) findings in patients with fibular stress injuries. MATERIALS AND METHODS/METHODS:The study group consisted of 20 patients with clinically diagnosed fibular stress injuries who were evaluated with MRI. Radiographs were performed in 14 of the 20 patients. The MRI examinations and radiographs were retrospectively reviewed in consensus by two musculoskeletal radiologists. RESULTS:All 20 patients with clinically diagnosed fibular stress injuries had periosteal edema and bone marrow edema within the fibula on MRI. The periosteal reaction and bone marrow edema were present within the distal fibula in 14 patients, the middle fibula in 1 patient, and the proximal fibula in 5 patients. The periosteal reaction was located on the anterior cortex in 1 patient, the posterior cortex in 4 patients, the lateral cortex in 11 patients, and circumferentially distributed throughout the cortex in 4 patients. Nine patients had abnormal T1 and T2 signal intensity within the fibular cortex. Initial and follow-up radiographs showed periosteal reaction in 15% and 50% of patients with fibular stress injuries respectively. CONCLUSIONS:The majority of fibular stress injuries involve the lateral cortex of the distal fibula.

PURPOSE/OBJECTIVE:To retrospectively compare the sensitivity and specificity of previously described magnetic resonance (MR) imaging criteria for the detection of instability in patients with juvenile or adult osteochondritis dissecans (OCD) of the knee, with arthroscopic findings as the reference standard. MATERIALS AND METHODS/METHODS:Informed consent was waived by the Institutional Review Board for this HIPAA-compliant study. The study group consisted of 32 skeletally immature patients (25 boys, seven girls; mean age, 14.4 years) with 36 juvenile OCD lesions of the knee and 33 skeletally mature patients (25 men, eight women; mean age, 26.2 years) with 34 adult OCD lesions of the knee. All patients had been evaluated with MR imaging and arthroscopy. MR studies were retrospectively reviewed by two radiologists in consensus to determine the presence of previously described MR imaging criteria for OCD instability (ie, high T2 signal intensity rim, surrounding cysts, high T2 signal intensity cartilage fracture line, and fluid-filled osteochondral defect). Sensitivity and specificity of the criteria were calculated separately for juvenile and adult OCD lesions. RESULTS:Separately, previously described MR imaging criteria for detection of OCD instability were 0%-88% sensitive and 21%-100% specific for juvenile OCD lesions and 27%-54% sensitive and 100% specific for adult OCD lesions. When used together, the criteria were 100% sensitive and 11% specific for instability in juvenile OCD lesions and 100% sensitive and 100% specific for instability in adult OCD lesions. CONCLUSION/CONCLUSIONS:Previously described MR imaging criteria for OCD instability have high specificity for adult but not juvenile lesions of the knee.

OBJECTIVE:To compare the magnetic resonance (MR) imaging findings of a group of patients with clinically diagnosed peroneal tendonopathy and peroneal tenosynovitis with the MR imaging findings of a control group of patients with no clinical evidence of peroneal tendon disorder. SUBJECTS AND METHODS/METHODS:The MR examinations of 24 patients with symptomatic peroneal tendinopathy or peroneal tenosynovitis and 70 patients with no clinical evidence of peroneal tendon disorder were retrospectively reviewed to determine the presence or absence of four MR imaging findings: 1) predominantly or uniform intermediate signal intensity within the peroneal tendons on one or more axial proton density-weighted images, 2) predominantly or uniform intermediate signal intensity within the peroneal tendons on three consecutive axial proton density-weighted images, 3) intermediate T2 signal intensity within the peroneal tendons, and 4) circumferential fluid within the common peroneal tendon sheath greater than 3 mm in maximal width. The sensitivity and specificity of these MR imaging findings for determining the presence or absence or symptomatic peroneal tendinopathy or peroneal tenosynovitis were calculated. RESULTS:The sensitivity of MR imaging findings 1, 2, 3, and 4 for determining the presence of peroneal tendinopathy or peroneal tenosynovitis were 92%, 92%, 50%, and 17% respectively. The specificity of MR imaging findings 1, 2, 3, and 4 for determining the absence of peroneal tendinopathy or peroneal tenosynovitis were 57%, 79%, 93%, and 100% respectively. CONCLUSION/CONCLUSIONS:The presence of predominantly or uniform intermediate signal intensity within the peroneal tendons on three consecutive axial proton density-weighted images is a highly sensitive and moderately specific indicator of symptomatic peroneal tendinopathy. The presence of intermediate T2 signal within the peroneal tendons, and the presence of circumferential fluid within the peroneal tendon sheath greater than 3 mm in maximal width, are highly specific indicators of peroneal tendinopathy and peroneal tenosynovitis respectively.

OBJECTIVE:The objective was to correlate radiographic findings with magnetic resonance imaging (MRI) findings in patients with suspected tibial stress injuries in order to determine the significance of radiographic signs of stress injury in these individuals. PATIENTS AND METHODS/METHODS:The study group consisted of 80 patients with suspected tibial stress injuries who underwent a radiographic and MR examination of the tibia. Nineteen patients had bilateral involvement. Thus, a total of 99 tibias were evaluated. All radiographs and MR examinations were retrospectively reviewed, 1 month apart, in consensus by two musculoskeletal radiologists. The radiographs were reviewed without knowledge of the site of the clinical symptoms. Fisher's exact tests were used to determine the association between a positive radiograph and the presence of various MRI signs of a high-grade stress injury. RESULTS:There was a strong association between the presence of periosteal reaction on radiographs at the site of the clinical symptoms and a Fredericson grade 4 stress injury on MRI. CONCLUSIONS:The presence of periosteal reaction on radiographs at the site of clinical symptoms is predictive of a high-grade stress injury by MRI criteria.

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.

The consistency of off-axis MRI with non-Cartesian sequences across a large number of scanners is highly variable. Improper timing alignment of the gradient fields, data acquisition system, and real-time frequency demodulation reference signal, which are necessary for off-axis imaging, is an important source of this variability. In addition, eddy currents and anisotropic gradient delays cause deviations in k-space trajectories that in turn make the demodulation reference signals inaccurate. A method is presented to quickly measure the timing error in the frequency demodulation reference signal and separate it from anisotropic gradient delays. k-Space deviations, as measured with a previous gradient calibration technique, are shown to be a second source of demodulation phase errors that degrade image quality. Using the timing delay and k-space deviations, a retrospective phase correction is applied to each k-space sample before the data are regridded during reconstruction. The timing delays of four MR scanners were measured to be 4.2-7.5 micros below the manufacturer's suggested delay. Significant degradation in 3D radial (3D projection reconstruction (PR)) knee and breast images are retrospectively corrected while a partial prospective correction is applied for spiral imaging. The method allows for more consistent performance of non-Cartesian sequences across multiple scanners without operator intervention.

OBJECTIVE:The objective of this article is to discuss the acquisition of high-quality MR images of the musculoskeletal system with uniform fat suppression using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). IDEAL is a three-point water-fat separation method that provides robust fat suppression even in the complex magnetic environments commonly encountered during clinical musculoskeletal imaging. CONCLUSION/CONCLUSIONS:The IDEAL technique provides uniform fat saturation even in complex magnetic environments and simultaneously produces in-phase and opposed-phase images that may be useful for characterization of osseous lesions. The IDEAL water-fat separation method is highly versatile and has been successfully combined with T1-weighted, T2-weighted, steady-state free precession, and spoiled gradient-recalled echo techniques to produce high-quality MR images in clinically acceptable scanning times.

PURPOSE/OBJECTIVE:To retrospectively determine at magnetic resonance (MR) imaging the prevalence of subchondral bone marrow edema beneath arthroscopically proved articular cartilage defects. MATERIALS AND METHODS/METHODS:The study was performed in compliance with HIPAA regulations, and a waiver of informed consent was obtained from the institutional review board before the study was performed. The study consisted of 132 patients (70 men, 62 women; average age, 53 years) with articular cartilage defects of the knee joint who underwent MR imaging of the knee and subsequent arthroscopic knee surgery. At the time of arthroscopy, each articular cartilage lesion was graded by using the Noyes classification system. MR examinations were retrospectively reviewed to determine the size, depth, and location of subchondral bone marrow edema without knowledge of the arthroscopic findings. Pairwise Fisher exact tests and two-sample t tests were used to correlate MR imaging findings of subchondral bone marrow edema with the arthroscopic grade of articular cartilage degeneration. RESULTS:Subchondral bone marrow edema was seen beneath 105 (19%) of 554 articular cartilage defects identified at arthroscopy. It was not observed beneath any of the six grade 1 cartilage defects but was observed beneath eight (4.9%) of 163 grade 2A defects, 40 (14.4%) of 278 grade 2B defects, 54 (55.1%) of 98 grade 3A defects, and three (33.3%) of nine grade 3B defects. Subchondral bone marrow edema was also seen beneath four (1.4%) of 238 articular surfaces that appeared normal at arthroscopy. The mean depth and cross-sectional area of subchondral bone marrow edema increased with increasing grade of the articular cartilage lesion. CONCLUSION/CONCLUSIONS:Higher grades of articular cartilage defects are associated with higher prevalence and greater depth and cross-sectional area of subchondral bone marrow edema.