Faculty Bibliography

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

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.

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.

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.

Introduction: Diagnostic laparoscopy (DL) is an increasingly used modality when approaching penetrating anterior abdominal injury (PAAI). Historically, exploratory laparotomy (EL) for PAAI can result in a 20% negative laparotomy, 5% mortality and 20% morbidity rate. Laparoscopically trained trauma surgeons can utilize a minimally invasive technique to quickly assess for intra-abdominal organ injury in hemodynamically stable patients. In the hands of a skilled surgeon, PAAI with a confirmed injury can be repaired through therapeutic laparoscopy (TL) or EL without delay in treatment. This study analyzes the safety and efficacy of using DL as a first line therapy for hemodynamically stable patients with PAAI. Methods: Between December 2006 and September 2016, 56 patients underwent DL after presenting to NYU Langone Hospital-Brooklyn Emergency Room with PAAI. A retrospective analysis was conducted to analyze protocol and treatment outcomes. Variables reviewed included Glasgow Coma Scale (GCS), Injury Severity Scale (ISS), FAST exam and/or CT scan results, length of stay (LOS), and postoperative complications. Based on outcomes, patients were cate-gorized into three groups: DL, DL with progression to TL, and DL with conversion to EL. Results: In the study period, a total of 94 patients presented with PAAI that went to the OR, 56 of which were initially treated laparoscopically. Causes of injury included stab wounds, gunshot wounds, traffic accidents, and self-inflicted injuries. The mean age was 40 +/- 12 years. The mean GCS was 14 +/- 2, and the mean ISS was 4 +/- 4. Of the 56 patients who underwent DL, 25 patients (44.6%) required no further intervention (group 1), 21 patients (37.5%) underwent TL (group 2), and 10 patients (17.8%) required EL (group 3). Mean LOS for groups 1, 2 and 3 were 4 +/- 3.3 days, 3 +/- 1.9 days and 6 +/- 4.5 days, respectively. There were no missed injuries or postoperative complications requiring the OR in all groups. TL included diaphragm laceration repairs, control of hepatic laceration and primary bowel repair. Conclusion: Diagnostic Laparoscopy should be considered first line for hemodynamically stable patients with PAAI with equivocal FAST and/or CT scan findings. Eighty-two percent of our patients did not require conversion to EL. This allowed for decreased postoperative pain, quicker recovery time, and shorter hospital stays. When in the hands of laparoscopically trained trauma surgeons, these patients can be quickly and safely treated while avoiding any delays in diagnosis

Purpose To investigate whether assessment of bone strength with quantitative computed tomography (CT) in combination with dual-energy x-ray absorptiometry (DXA) is cost-effective as a screening tool for osteoporosis in postmenopausal women. Materials and Methods A state-transition microsimulation model of osteoporosis for postmenopausal women aged 55 years or older was developed with a lifetime horizon and U.S. societal perspective. All model inputs were derived from published literature. Three strategies were compared: no screening, DXA with T score-dependent rescreening intervals, and a combination of DXA and quantitative CT with different intervals (3, 5, and 10 years) at different screening initiation ages (55-65 years). Oral bisphosphonate therapy was started if DXA hip T scores were less than or equal to -2.5, 10-year risk for hip fracture was greater than 3% (World Health Organization Fracture Risk Assessment Tool score, or FRAX), 10-year risk for major osteoporotic fracture was greater than 20% (FRAX), quantitative CT femur bone strength was less than 3000 N, or occurrence of first fracture (eg, hip, vertebral body, wrist). Outcome measures were incremental cost-effectiveness ratios (ICERs) in 2015 U.S. dollars per quality-adjusted life year (QALY) gained and number of fragility fractures. Probabilistic sensitivity analysis was also performed. Results The most cost-effective strategy was combined DXA and quantitative CT screening starting at age 55 with quantitative CT screening every 5 years (ICER, $2000 per QALY). With this strategy, 12.8% of postmenopausal women sustained hip fractures in their remaining life (no screening, 18.7%; DXA screening, 15.8%). The corresponding percentages of vertebral fractures for DXA and quantitative CT with a 5-year interval, was 7.5%; no screening, 11.1%; DXA screening, 9%; for wrist fractures, 14%, 17.8%, and 16.4%, respectively; for other fractures, 22.6%, 30.8%, and 27.3%, respectively. In probabilistic sensitivity analysis, DXA and quantitative CT at age 55 years with quantitative CT screening every 5 years was the best strategy in more than 90% of all 1000 simulations (for thresholds of $50 000 per QALY and $100 000 per QALY). Conclusion Combined assessment of bone strength and bone mineral density is a cost-effective strategy for osteoporosis screening in postmenopausal women and has the potential to prevent a substantial number of fragility fractures. (c) RSNA, 2017 Online supplemental material is available for this article.

The goal of this paper was to evaluate the possibility of bi-component T1rho and T2 relaxation mapping of human skeletal muscle at 3 T in clinically feasible scan times. T1rho- and T2-weighted images of calf muscle were acquired using a modified 3D-SPGR sequence on a standard 3 T clinical MRI scanner. The mono- and biexponential models were fitted pixel-wise to the series of T1rho and T2 weighted images. The biexponential decay of T1rho and T2 relaxations was detected in ~30% and ~40% of the pixels across all volunteers, respectively. Monoexponential and bi-exponential short and long T1rho relaxation times were estimated to be 26.9 ms, 4.6 ms (fraction 22%) and 33.2 ms (fraction: 78%), respectively. Similarly, the mono- and bi-exponential short and long T2 relaxation times were 24.7 ms, 4.2 ms (fraction 15%) and 30.4 ms (fraction 85%) respectively. The experiments had good repeatability with RMSCV < 15% and ICC > 60%. This approach could potentially be used in exercise intervention studies or in studies of inflammatory myopathies or muscle fibrosis, permitting greater sensitivity and specificity via measurement of different water compartments and their fractions.

The purpose of this study was to demonstrate the feasibility of biexponential T1rho relaxation mapping of human knee cartilage in vivo. A three-dimensional, customized, turbo-flash sequence was used to acquire T1rho -weighted images from healthy volunteers employing a standard 3-T MRI clinical scanner. A series of T1rho -weighted images was fitted using monoexponential and biexponential models with two- and four-parametric non-linear approaches, respectively. Non-parametric Kruskal-Wallis and Mann-Whitney U-statistical tests were used to evaluate the regional relaxation and gender differences, respectively, with a level of significance of P = 0.05. Biexponential relaxations were detected in the cartilage of all volunteers. The short and long relaxation components of T1rho were estimated to be 6.9 and 51.0 ms, respectively. Similarly, the fractions of short and long T1rho were 37.6% and 62.4%, respectively. The monoexponential relaxation of T1rho was 32.6 ms. The experiments showed good repeatability with a coefficient of variation (CV) of less than 20%. A biexponential relaxation model showed a better fit than a monoexponential model to the T1rho relaxation decay in knee cartilage. Biexponential T1rho components could potentially be used to increase the specificity to detect early osteoarthritis by the measurement of different water compartments and their fractions.

Osteoporosis is a disease of weak bone and increased fracture risk caused by low bone mass and microarchitectural deterioration of bone tissue. The standard-of-care test used to diagnose osteoporosis, dual-energy x-ray absorptiometry (DXA) estimation of areal bone mineral density (BMD), has limitations as a tool to identify patients at risk for fracture and as a tool to monitor therapy response. Magnetic resonance imaging (MRI) assessment of bone structure and microarchitecture has been proposed as another method to assess bone quality and fracture risk in vivo. MRI is advantageous because it is noninvasive, does not require ionizing radiation, and can evaluate both cortical and trabecular bone. In this review article, we summarize and discuss research progress on MRI of bone structure and microarchitecture over the last decade, focusing on in vivo translational studies. Single-center, in vivo studies have provided some evidence for the added value of MRI as a biomarker of fracture risk or treatment response. Larger, prospective, multicenter studies are needed in the future to validate the results of these initial translational studies. LEVEL OF EVIDENCE: 5 J. Magn. Reson. Imaging 2016.