Faculty Bibliography

BACKGROUND:ρ along with the morphological assessment can potentially be used as noninvasive biomarkers in detecting early-stage OA. To correlate the biochemical and morphological data, submillimeter isotropic resolution for both studies is required. PURPOSE/OBJECTIVE:ρ relaxometry of human knee cartilage in vivo. STUDY TYPE/METHODS:Prospective. POPULATION/METHODS:Ten healthy volunteers with no known inflammation, trauma, or pain in the knee. FIELD STRENGTH/SEQUENCE/UNASSIGNED:ρ-weighted images on a 3T MRI scanner. ASSESSMENT/RESULTS:ρ relaxations were assessed in the articular cartilage of 10 healthy volunteers. STATISTICAL TESTS/UNASSIGNED:Nonparametric rank-sum tests. Bland-Altman analysis and coefficient of variation. RESULTS:for volume, and -0.78 mm and +0.46 mm for thickness, respectively. DATA CONCLUSION/UNASSIGNED:ρ relaxation of knee joint with 0.7 × 0.7 × 0.7 mm isotropic spatial resolution is demonstrated in vivo. Comparison with a standard method showed that the proposed technique is suitable for assessing the volume and thickness of articular cartilage. LEVEL OF EVIDENCE/METHODS:2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;00:000-000.

Background Bone remodels in response to mechanical loads and osteoporosis results from impaired ability of bone to remodel. Bone microarchitecture analysis provides information on bone quality beyond bone mineral density (BMD). Purpose To compare subchondral bone microarchitecture parameters in the medial and lateral tibia plateau in individuals with and without fragility fractures. Material and Methods Twelve female patients (mean age = 58 ± 15 years; six with and six without previous fragility fractures) were examined with dual-energy X-ray absorptiometry (DXA) and 7-T magnetic resonance imaging (MRI) of the proximal tibia. A transverse high-resolution three-dimensional fast low-angle shot sequence was acquired (0.234 × 0.234 × 1 mm). Digital topological analysis (DTA) was applied to the medial and lateral subchondral bone of the proximal tibia. The following DTA-based bone microarchitecture parameters were assessed: apparent bone volume; trabecular thickness; profile-edge-density (trabecular bone erosion parameter); profile-interior-density (intact trabecular rods parameter); plate-to-rod ratio; and erosion index. We compared femoral neck T-scores and bone microarchitecture parameters between patients with and without fragility fracture. Results There was no statistical significant difference in femoral neck T-scores between individuals with and without fracture (-2.4 ± 0.9 vs. -1.8 ± 0.7, P = 0.282). Apparent bone volume in the medial compartment was lower in patients with previous fragility fracture (0.295 ± 0.022 vs. 0.317 ± 0.009; P = 0.016). Profile-edge-density, a trabecular bone erosion parameter, was higher in patients with previous fragility fracture in the medial (0.008 ± 0.003 vs. 0.005 ± 0.001) and lateral compartment (0.008 ± 0.002 vs. 0.005 ± 0.001); both P = 0.025. Other DTA parameters did not differ between groups. Conclusion 7-T MRI and DTA permit detection of subtle changes in subchondral bone quality when differences in BMD are not evident.

Purpose To determine if 3-T magnetic resonance (MR) imaging of proximal femur microarchitecture can allow discrimination of subjects with and without fragility fracture who do not have osteoporotic proximal femur bone mineral density (BMD). Materials and Methods Sixty postmenopausal women (30 with and 30 without fragility fracture) who had BMD T scores of greater than -2.5 in the hip were recruited. All subjects underwent dual-energy x-ray absorptiometry to assess BMD and 3-T MR imaging of the same hip to assess bone microarchitecture. World Health Organization Fracture Risk Assessment Tool (FRAX) scores were also computed. We used the Mann-Whitney test, receiver operating characteristics analyses, and Spearman correlation estimates to assess differences between groups, discriminatory ability with parameters, and correlations among BMD, microarchitecture, and FRAX scores. Results Patients with versus without fracture showed a lower trabecular plate-to-rod ratio (median, 2.41 vs 4.53, respectively), lower trabecular plate width (0.556 mm vs 0.630 mm, respectively), and lower trabecular thickness (0.114 mm vs 0.126 mm) within the femoral neck, and higher trabecular rod disruption (43.5 vs 19.0, respectively), higher trabecular separation (0.378 mm vs 0.323 mm, respectively), and lower trabecular number (0.158 vs 0.192, respectively), lower trabecular connectivity (0.015 vs 0.027, respectively) and lower trabecular plate-to-rod ratio (6.38 vs 8.09, respectively) in the greater trochanter (P < .05 for all). Trabecular plate-to-rod ratio, plate width, and thickness within the femoral neck (areas under the curve [AUCs], 0.654-0.683) and trabecular rod disruption, number, connectivity, plate-to-rod ratio, and separation within the greater trochanter (AUCs, 0.662-0.694) allowed discrimination of patients with fracture from control subjects. Femoral neck, total hip, and spine BMD did not differ between and did not allow discrimination between groups. FRAX scores including and not including BMD allowed discrimination between groups (AUCs, 0.681-0.773). Two-factor models (one MR imaging microarchitectural parameter plus a FRAX score without BMD) allowed discrimination between groups (AUCs, 0.702-0.806). There were no linear correlations between BMD and microarchitectural parameters (Spearman ρ, -0.198 to 0.196). Conclusion 3-T MR imaging of proximal femur microarchitecture allows discrimination between subjects with and without fragility fracture who have BMD T scores of greater than -2.5 and may provide different information about bone quality than that provided by dual-energy x-ray absorptiometry.^©RSNA, 2018.

Purpose: To determine the relationships between textural 3T MRI derived measures of proximal femur bone quality and age, body mass index (BMI), and fracture risk. Materials and Methods: The study had institutional review board approval. The proximal femurs of 23 female subjects were imaged on a 3T MRI scanner. Scanning parameters were TR/TE=37ms/4.92ms, flip angle= 250, bandwidth=130Hz/pixel, field of view=120 mm, in-plane voxel dimension=0.775mmx0.775mm, parallel imaging (GRAPPA) factor=2, slice thickness=2 mm. 40 coronal slices were segmented using an inhouse software program (Fire Voxel). We computed mean bone volume, mean signal intensity (SI), and mean signal intensity inhomogeneity (standard deviation/mean) within volumes of interest for total, cortical, and trabecular compartments of the proximal femur. We used standard statistical methods to correlate these parameters with age, BMI, and FRAX hip fracture score. Results: Subjects' mean age was 60.9 years (SD +/- 9.9) and mean BMI was 22.9 kg/m² (SD +/-4.3). The mean total hip T-score was -1.9 (SD +/- 1.2). Higher BMI correlated with lower cortical SI inhomogeneity (r=0.66, p=0.0005). Higher age correlated with lower SI inhomogeneity of total, trabecular, and cortical bone compartments (r=0.51, p=0.01; r=0.43, p= 0.03; and r=0.45, 0.03 respectively). Higher FRAX score also correlated with lower cortical and total bone SI inhomogeneity. (r=0.50, p=0.03; r=0.53, p=0.02) A higher total hip T-score correlated with lower total bone SI inhomogeneity (r=0.46, p=0.02). There was no significant correlation with cortical or trabecular bone SI inhomogeneity (p=0.4, p=0.097 respectively). Conclusion: Lower MRI-computed proximal femur SI inhomogeneity correlates with higher age, BMI, FRAX score and total hip BMDT-score. This may reflect the ability of textural metrics computed from 3TMRI to detect changes in bone quality with changes in age, BMI, and fracture risk. Larger cohort studies are needed to confirm these results

Purpose: To evaluate biexponential T2 relaxation mapping of human knee menisci in vivo in clinically feasible scan times Materials and Methods: The study was approved by the Institutional Review Board and informed consent was obtained from eight 8 healthy volunteers (4 male&4 female, mean age 30+/-4 years, mean weight 63+/-15 kg). T2-weighted MRI of the knee was acquired using a Siemens Prisma 3TMRI scanner. A 3D Turbo-Flash sequence was modified to enable T2- weighted imaging at 10 different echo times. Ten meniscal regions of interest were assessed: the red and white zones of the anterior and posterior horns, and the body of both the medial and lateral menisci. Series of T2-weighted images were fitted using mono- and biexponential models with two- and four- parametric nonlinear approaches, respectively. Results: Biexponential relaxation of T2 was detected in the knee menisci in 10 regions of interest in all eight healthy volunteers. Global short/long relaxation components of T2 were estimated to be 6.1 / 57.2 msec with corresponding fractions of 65.16% / 34.84%, respectively. The global monoexponential relaxation of T2 was measured to be 19.8 msec. Significant differences were observed in T2 relaxation between different regions of interest. Conclusion: Biexponential relaxation of T2 was observed in the human menisci in vivo. The short and long components are thought to be related to the tightly bound and loosely bound macromolecular water compartments respectively. These preliminary results of biexponential T2 analysis could potentially be used to increase the specificity for detection of early meniscal degeneration by measuring different water compartments and their fractions

Background/UNASSIGNED:Digital templating systems foster patient-specific measurements for preoperative planning. Questions/Purposes/UNASSIGNED:We aim (1) to verify the accuracy of a templating system, (2) to describe the effects of scaling marker position on the accuracy of digital templating of the hip, and (3) to provide a practical guide for scaling marker position using patient body mass index (BMI). Methods/UNASSIGNED:A scaling sphere was placed in five positions along the anterior-posterior axis of an acetabular implant and pelvis phantom, and x-rays were obtained. Each radiograph was templated for the acetabular component and recorded. A retrospective review identified CT scans of preoperative hip arthroplasty cases. The center of the greater trochanter was calculated from these CT scans as the percent distance from the anterior thigh and recorded with the patient's BMI. Results/UNASSIGNED:By centering the scaling sphere on the acetabular component, an accurate cup size was achieved. A difference of 3.5 cm in sphere placement resulted in a full cup size magnification error. Positioning the scaling sphere at the level of the pubic symphysis resulted in a difference of four cup sizes. This patient population had an average BMI of 28.72 kg/m2 (standard deviation 6.26 kg/m2) and an average position of the center of the greater trochanter of 51% (standard deviation of 6%) from the anterior surface of thigh. Conclusions/UNASSIGNED:Digital templating relies on scaling marker position to accurately estimate implant size. Based on the findings in this study, scaling markers for hip imaging should be placed laterally, mid-thigh in the anterior-posterior direction for patients with a BMI between 25 and 40 kg/m2. If abnormal hip anatomy or extremes of BMI are discovered, then scaling sphere positioning should be optimized on a case-by-case basis. Digital templating systems for total hip arthroplasty must use precisely placed scaling markers at the level of the hip joint to allow for accurate implant size estimation.

PURPOSE/OBJECTIVE:To compare patellar instability with magnetic resonance imaging analysis using continuous real-time radial gradient-echo (GRE) imaging in the assessment of symptomatic patients and asymptomatic subjects. METHODS:Symptomatic patients with suspected patellofemoral maltracking and asymptomatic volunteers were scanned in real time by a radial 2-dimensional GRE sequence at 3 T in axial orientation at the patella level through a range of flexion-extension. The degree of lateral maltracking, as well as the associated tibial tubercle-trochlear groove distance and trochlea depth, was measured. Patellar lateralization was categorized as normal (≤2 mm), mild (>2 to ≤5 mm), moderate (>5 to ≤10 mm), or severe (>10 mm). The patellofemoral cartilage was also assessed according to the modified Outerbridge grading system. RESULTS:The study included 20 symptomatic patients (13 women and 7 men; mean age, 36 ± 12.8 years) and 10 asymptomatic subjects (3 women and 7 men; mean age, 33.1 years). The mean time to perform the dynamic component ranged from 3 to 7 minutes. Lateralization in the symptomatic group was normal in 10 patients, mild in 1, moderate in 8, and severe in 1. There was no lateral tracking greater than 3 mm in the volunteer group. Lateral maltracking was significantly higher in symptomatic patients than in asymptomatic subjects (4.4 ± 3.7 mm vs 1.5 ± 0.71 mm, P = .007). Lateral tracking significantly correlated with tibial tubercle-trochlear groove distance (r = 0.48, P = .006). There was excellent agreement on lateral tracking between the 2 reviewers (intraclass correlation coefficient, 0.979; 95% confidence interval, 0.956-0.990). CONCLUSIONS:The inclusion of a dynamic radial 2-dimensional GRE sequence is a rapid and easily performed addition to the standard magnetic resonance imaging protocol and allows dynamic quantitative assessment of patellar instability and lateral maltracking in symptomatic patients. With a paucity of reported data using this technique confirming that these results reach clinical significance, future work is required to determine how much lateral tracking is clinically significant. LEVEL OF EVIDENCE/METHODS:Level III, case control.

OBJECTIVES: To evaluate the potential of sodium MRI to detect changes over time of apparent sodium concentration (ASC) in articular cartilage in patients with knee osteoarthritis (OA). METHODS: The cartilage of 12 patients with knee OA were scanned twice over a period of approximately 16 months with two sodium MRI sequences at 7 T: without fluid suppression (radial 3D) and with fluid suppression by adiabatic inversion recovery (IR). Changes between baseline and follow-up of mean and standard deviation of ASC (in mM), and their rate of change (in mM/day), were measured in the patellar, femorotibial medial and lateral cartilage regions for each subject. A matched-pair Wilcoxon signed rank test was used to assess significance of the changes. RESULTS: Changes in mean and in standard deviation of ASC, and in their respective rate of change over time, were only statistically different when data was acquired with the fluid-suppressed sequence. A significant decrease (p = 0.001) of approximately 70 mM in mean ASC was measured between the two IR scans. CONCLUSION: Quantitative sodium MRI with fluid suppression by adiabatic IR at 7 T has the potential to detect a decrease of ASC over time in articular cartilage of patients with knee osteoarthritis. KEY POINTS: * Sodium MRI can detect apparent sodium concentration (ASC) in cartilage * Longitudinal study: sodium MRI can detect changes in ASC over time * Potential for follow-up studies of cartilage degradation in knee osteoarthritis.

PURPOSE: To evaluate biexponential T2 relaxation mapping of human knee cartilage in vivo in clinically feasible scan times. MATERIALS AND METHODS: T2 -weighted magnetic resonance (MR) images were acquired from eight healthy volunteers using a standard 3T clinical scanner. A 3D Turbo-Flash sequence was modified to enable T2 -weighted imaging with different echo times. Series of T2 -weighted images were fitted using mono- and biexponential models with two- and four-parametric nonlinear approaches, respectively. RESULTS: Biexponential relaxation of T2 was detected in the knee cartilage in five regions of interest in all eight healthy volunteers. Short/long relaxation components of T2 were estimated to be 8.27 +/- 0.68 / 45.35 +/- 3.79 msec with corresponding fractions of 41.3 +/- 1.1% / 58.6 +/- 4.6%, respectively. The monoexponential relaxation of T2 was measured to be 26.9 +/- 2.27 msec. The experiments showed good repeatability with coefficient of variation root mean square (CVrms ) < 18% in all regions. The only difference in gender was observed in medial tibial cartilage, where the biexponential T2 in female volunteers was significantly higher compared to male volunteers (P = 0.014). Significant differences were observed in T2 relaxation between different regions on interest. CONCLUSION: Biexponential relaxation of T2 was observed in the human knee cartilage in vivo. The short and long components are thought to be related to the tightly bound and loosely bound macromolecular water compartments. These preliminary results of biexponential T2 analysis could potentially be used to increase the specificity for detection of early osteoarthritis by measuring different water compartments and their fractions. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017.