Faculty Bibliography

During the previous 2 decades, numerous surgical procedures have become available to treat osteochondral lesions of the talus. The objective of the present study was to use 7 Tesla (7T) magnetic resonance imaging (MRI) to quantify and compare T2 values (a marker of collagen architecture) of native tibiotalar cartilage and cartilage repair tissue in patients treated with a juvenile particulate allograft for osteochondral lesions of the talus. The institutional review board approved the present study, and all subjects provided written informed consent. We scanned the ankles of 7 cartilage repair patients using a 7T MRI scanner with a multi-echo spin-echo sequence to measure the cartilage T2 values. We assessed the cartilage T2 values in the talar repair tissue, adjacent native talar cartilage, and overlying tibial cartilage. We compared the differences between groups using the paired t test. The talar cartilage repair tissue demonstrated greater mean T2 relaxation times compared with the native adjacent talar cartilage (64.88 +/- 12.23 ms versus 49.56 +/- 7.82 ms; p = .043). The tibial cartilage regions overlying these talar cartilage regions demonstrated a trend toward greater T2 relaxation times (77.00 +/- 31.29 ms versus 59.52 +/- 7.89 ms; p = .067). 7T MRI can detect differences in T2 values in cartilage repair tissue compared with native cartilage and could be useful for monitoring the status of cartilage health after surgical intervention.

Purpose To describe a nonlinear finite element analysis method by using magnetic resonance (MR) images for the assessment of the mechanical competence of the hip and to demonstrate the reproducibility of the tool. Materials and Methods This prospective study received institutional review board approval and fully complied with HIPAA regulations for patient data. Written informed consent was obtained from all subjects. A nonlinear finite element analysis method was developed to estimate mechanical parameters that relate to hip fracture resistance by using MR images. Twenty-three women (mean age +/- standard deviation, 61.7 years +/- 13.8) were recruited from a single osteoporosis center. To thoroughly assess the reproducibility of the finite element method, three separate analyses were performed: a test-retest reproducibility analysis, where each of the first 13 subjects underwent MR imaging on three separate occasions to determine longitudinal variability, and an intra- and interoperator reproducibility analysis, where a single examination was performed in each of the next 10 subjects and four operators independently performed the analysis two times in each of the subjects. Reproducibility of parameters that reflect fracture resistance was assessed by using the intraclass correlation coefficient and the coefficient of variation. Results For test-retest reproducibility analysis and inter- and intraoperator analyses for proximal femur stiffness, yield strain, yield load, ultimate strain, ultimate load, resilience, and toughness in both stance and sideways-fall loading configurations each had an individual median coefficient of variation of less than 10%. Additionally, all measures had an intraclass correlation coefficient higher than 0.99. Conclusion This experiment demonstrates that the finite element analysis model can consistently and reliably provide fracture risk information on correctly segmented bone images. (c) RSNA, 2016 Online supplemental material is available for this article.

Transient osteoporosis (TO) is a clinical syndrome characterized by joint pain and the presence of bone marrow edema on magnetic resonance imaging (MRI), both of which spontaneously resolve over time. Transient osteoporosis most commonly affects the hip, but also may involve other lower extremity sites. TO likely represents a disorder that may be monoarticular or "migratory" with involvement of two or more lower extremity sites sequentially affected over a number of months. We report on two cases of transient osteoporosis, one involving the knee and one involving the hip, demonstrating the utility of serial bone mineral density measurements at both sites. Additionally, we are able to report on the microarchitectural changes seen at the distal femur on ultra-high resolution (7 T) MRI. Case #1 describes a recurrence of transient osteoporosis of the hip three years after a similar presentation at the contralateral hip and highlights the findings of rapidly changing bone mineral density in this clinical syndrome. In contrast to the spine, hip and forearm, peripheral bone density measurements at the knee are rarely reported and to our knowledge Case #2 represents the first report of transient osteoporosis of the knee demonstrating bone density findings similar to that seen in the hip. We postulate that transient osteoporosis of the knee is part of a clinical spectrum most commonly seen in the hip and one that is marked by lower extremity joint pain, bone marrow edema on MRI and transient decreases in bone mineral density all of which spontaneously resolve without sequelae.

BACKGROUND: Digital templating systems have been promoted due to their ability to reduce costs, facilitate preoperative planning, and maintain surgical accuracy. The implementation of a templating system at a large institution is complicated and has not been fully described. PURPOSE: We aim to explain the requisite collaboration between orthopaedic surgery, radiology, and information technology needed to implement a successful orthopaedic templating system at a large institution. METHODS: A search of the PubMed database was performed to provide a comprehensive review of digital templating. Furthermore, we offer the organizational and technical details needed to implement an institutional templating system. RESULTS: We have provided a strategic plan to describe the collaboration between orthopaedic surgery, musculoskeletal radiology, and information technology required for a successful templating system. CONCLUSIONS: The transition to digital templating requires planning, training, and communication between multiple disciplines. Digital templating systems have the potential to foster preoperative planning, improve trainee education, and reduce departmental costs. CLINICAL SIGNIFICANCE: Preoperative digital templating is a means to reduce the risk of intraoperative fracture, decrease overall surgical time, and plan for implant size prior to surgery.

Osteoporosis is associated with increased risk of fractures, which is clinically defined by low bone mineral density. Increasing evidence suggests that trabecular bone (TB) micro-architecture is an important determinant of bone strength and fracture risk. We present an improved volumetric topological analysis algorithm based on fuzzy skeletonization, results of its application on in vivo MR imaging, and compare its performance with digital topological analysis. The new VTA method eliminates data loss in the binarization step and yields accurate and robust measures of local plate-width for individual trabeculae, which allows classification of TB structures on the continuum between perfect plates and rods. The repeat-scan reproducibility of the method was evaluated on in vivo MRI of distal femur and distal radius, and high intra-class correlation coefficients between 0.93 and 0.97 were observed. The method's ability to detect treatment effects on TB micro-architecture was examined in a 2 years testosterone study on hypogonadal men. It was observed from experimental results that average plate-width and plate-to-rod ratio significantly improved after 6 months and the improvement was found to continue at 12 and 24 months. The bone density of plate-like trabeculae was found to increase by 6.5% (p = 0.06), 7.2% (p = 0.07) and 16.2% (p = 0.003) at 6, 12, 24 months, respectively. While the density of rod-like trabeculae did not change significantly, even at 24 months. A comparative study showed that VTA has enhanced ability to detect treatment effects in TB micro-architecture as compared to conventional method of digital topological analysis for plate/rod characterization in terms of both percent change and effect-size.

Purpose: Elevated bone marrow fat content and elevated intramuscular fat content increase the risk for osteoporotic fracture, but it is unknown if such changes are associated with detrimental changes in bone microarchitecture and bone mass. Our goal was to determine the association between femoral neck bone marrow fat fraction and gluteal muscle fat fraction with: 1) femoral neck bone microarchitecture and 2) femoral neck bone mineral density (BMD). Materials and Methods: This study was HIPAA compliant and institutional review board approved. Written informed consent was obtained. Hips of forty-two consecutive patients referred from the osteoporosis clinic at our institution (mean-age 60.2 +/- 7.5 years) underwent dual-energy X-ray absorptiometry (DXA), high-spatial resolution three-dimensional 3 T MRI with volumetric topological analysis (VTA-MRI), and fat quantification with IDEAL-MRI. Femoral neck BMD T-scores (DXA) and trabecular bone microarchitecture parameters (VTA-MRI) were calculated. Proton density fat fractions (IDEAL-MRI) of the femoral neck bone marrow (FFmarrow) and the gluteus maximus muscle (FFmuscle) were measured by two independent readers. Interreader agreement was calculated using intraclass correlation coefficients (ICC). FFmarrow and FFmuscle were correlated with BMD, bone microarchitecture parameters, age, and body-massindex (BMI). Results: FFmarrow (mean from both readers 70.2 +/- 6.5 %) and FFmuscle (11.3 +/- 3.8 %) measurements showed excellent interreader agreement (ICC = 0.955/0.995; both p < 0.0005). No statistically significant correlation between FFmarrow and BMD was found (r = -0.257, p = 0.155). Age- and BMI-adjusted FFmarrow inversely correlated with trabecular plate-to-rod ratio (r = -0.335; p = 0.049) and trabecular plate-width (r = -0.345; p = 0.042), but not with bone volume fraction (r = 0.155; p = 0.374). FFmarrow correlated with age (r = 0.383; p = 0.021), but not with BMI (r = 0.132; p = 0.445). FFmuscle showed no correlation with BMD or bone microarchitecture. FFmuscle was independently correlated with BMI (r = 0.557; <0.0005) and age (r = 0.438; p = 0.008). Conclusion: Bone marrow fat content inversely correlated with trabecular plate-to-rod ratio and plate-width, but not BMD, suggesting that the increased fracture risk in the setting of elevated bone marrow fat content may in part be mediated via microarchitectural deterioration, rather than via reduced BMD. Gluteal muscle fat content did not correlate with changes in femoral neck microarchitecture or BMD, suggesting that intramuscular fat content may increase fracture risk independent of detrimental changes in bone microarchitecture and BMD. Overall, highresolution 3 T MRI of bone microarchitecture combined with IDEAL-based fat quantification can help provide insight into the relationship between adipose bone marrow, lean muscle mass, and possible mechanisms of osteoporotic fracture risk in vivo

PURPOSE: We describe a 2 x 6 channel sodium/proton array for knee MRI at 3T. Multielement coil arrays are desirable because of well-known signal-to-noise ratio advantages over volume and single-element coils. However, low tissue-coil coupling that is characteristic of coils operating at low frequency can make the potential gains from a phased array difficult to realize. METHODS: The issue of low tissue-coil coupling in the developed six-channel sodium receive array was addressed by implementing 1) a mechanically flexible former to minimize the coil-to-tissue distance and reduce the overall diameter of the array and 2) a wideband matching scheme that counteracts preamplifier noise degradation caused by coil coupling and a high-quality factor. The sodium array was complemented with a nested proton array to enable standard MRI. RESULTS: The wideband matching scheme and tight-fitting mechanical design contributed to >30% central signal-to-noise ratio gain on the sodium module over a mononuclear sodium birdcage coil, and the performance of the proton module was sufficient for clinical imaging. CONCLUSION: We expect the strategies presented in this study to be generally relevant in high-density receive arrays, particularly in x-nuclei or small animal applications. Magn Reson Med, 2015. (c) 2015 Wiley Periodicals, Inc.

Automating the process of femoroacetabular cartilage identification from magnetic resonance imaging (MRI) images has important implications to guiding clinical care by providing a temporal metric that allows for optimizing the timing for joint preservation surgery. In this paper, we evaluate a new automated cartilage segmentation method using a time trial, segmented volume comparison, overlap metrics, and Euclidean distance mapping. We report interrater overlap metrics using the true fast imaging with steady-state precession MRI sequence of 0.874, 0.546, and 0.704 for the total overlap, union overlap, and mean overlap, respectively. This method was 3.28x faster than manual segmentation. This technique provides clinicians with volumetric cartilage information that is useful for optimizing the timing for joint preservation procedures.

BACKGROUND: Glucocorticoid-induced osteoporosis (GIO) is the most common secondary form of osteoporosis, and glucocorticoid users are at increased risk for fracture compared with nonusers. There is no established relationship between bone mineral density (BMD) and fracture risk in GIO. We used 3 Tesla (T) MRI to investigate how proximal femur microarchitecture is altered in subjects with GIO. METHODS: This study had institutional review board approval. We recruited 6 subjects with long-term (> 1 year) glucocorticoid use (median age = 52.5 (39.2-58.7) years) and 6 controls (median age = 65.5 [62-75.5] years). For the nondominant hip, all subjects underwent dual-energy x-ray absorptiometry (DXA) to assess BMD and 3T magnetic resonance imaging (MRI, 3D FLASH) to assess metrics of bone microarchitecture and strength. RESULTS: Compared with controls, glucocorticoid users demonstrated lower femoral neck trabecular number (-50.3%, 1.12 [0.84-1.54] mm(-1) versus 2.27 [1.88-2.73] mm(-1) , P = 0.02), plate-to-rod ratio (-20.1%, 1.48 [1.39-1.71] versus 1.86 [1.76-2.20], P = 0.03), and elastic modulus (-64.8% to -74.8%, 1.54 [1.22-3.19] GPa to 2.31 [1.87-4.44] GPa versus 6.15 [5.00-7.09] GPa to 6.59 [5.58-7.31] GPa, P < 0.05), and higher femoral neck trabecular separation (+192%, 0.705 [0.462-1.00] mm versus 0.241 [0.194-0.327] mm, P = 0.02). There were no differences in femoral neck trabecular thickness (-2.7%, 0.193 [0.184-0.217] mm versus 0.199 [0.179-0.210] mm, P = 0.94) or femoral neck BMD T-scores (+20.7%, -2.1 [-2.8 to -1.4] versus -2.6 [-3.3 to -2.5], P = 0.24) between groups. CONCLUSION: The 3T MRI can potentially detect detrimental changes in proximal femur microarchitecture and strength in long-term glucocorticoid users. J. MAGN. RESON. IMAGING 2015;42:1489-1496.