Ultrashort Echo Time Imaging of the Osteochondral Junction in Subjects with Knee Osteoarthritis and Age-matched Healthy Volunteers

SYNOPSIS We describe in vivo translation of ultrashort TE (UTE) imaging of the osteochondral junction (OCJ) at the knee in 9 subjects with osteoarthritis (OA) and 4 age-matched healthy volunteers. The OCJ plays an important role in onset and progression of OA. Our study demonstrates that UTE imaging of the OCJ is repeatable and demonstrates OCJ defects in OA subjects but not in healthy volunteers. Areas of OCJ damage commonly co-locate to other osteochondral pathology (bone marrow lesions and cartilage defects). UTE imaging of the OCJ may be a helpful tool for assessing OCJ damage in clinical studies of OA. INTRODUCTION Disruption of the osteochondral junction (OCJ) is thought to play an important role in the onset and progression of osteoarthritis (OA). Using conventional MR imaging, direct visualisation of the OCJ is not possible due to inherent short T1 and T2 relaxation times of the OCJ tissues. However, by achieving echo times (TEs) of < 1 ms, ultrashort echo time (UTE) MR imaging allows direct visualisation of the OCJ. The normal OCJ appears as an area of linear high signal intensity (SI) on UTE images at the bone-cartilage interface. In OA it has been shown that this area of linear high SI can become thinned or absent, compatible with histological findings of OCJ defects(1, 2). These findings have been described in a number of cadaveric MR studies, but there are limited in vivo data available(3-5). The aims of this study were to compare the in vivo appearance of the OCJ on UTE MR imaging between subjects with knee OA and age-matched healthy volunteers, to determine the relationship between OCJ defects and other osteochondral pathology, and to assess test-retest repeatability. METHODS We imaged 9 participants with mild-moderate knee osteoarthritis, characterised by radiographs with medial tibiofemoral compartment predominant disease and Kellgren-Lawrence grades 2-3, and 4 age-matched healthy volunteers. Participants were imaged at baseline and 1 month. MR studies were performed on a 3T system (GE 750, GE Healthcare). The MR protocol consisted of standard clinical sequences (coronal and sagittal intermediate-weighted fat-saturated fast spin echo (FSE) sequences plus a coronal T1-weighted FSE sequence) and a sagittal dual-echo UTE gradient echo sequence acquired using a 3D cones trajectory (research prototype; repetition time 15 ms, TE 0.03/4.5 ms, flip angle 13o, field-of-view 18 x 18 cm, matrix 430 x 430, slice thickness 2 mm, number of averages 1, acquisition time ~ 7.5 minutes). To increase conspicuity of short T2 tissues, we performed weighted digital image subtraction of the longer TE (4.5 ms) from the shorter TE images (0.03 ms)(6). The presence or absence of characteristic linear high SI at the OCJ was scored in 12 regions for each knee, corresponding to tibiofemoral subdivisions commonly used for semi-quantitative scoring. The presence of bone marrow lesions (BML) or cartilage defects in the same regions was also recorded. Assessment was performed by a single musculoskeletal radiologist with 5 years' experience in OA research, blinded to group assignment. We used descriptive statistics to compare the number of regions with OCJ defects in subjects with OA and healthy volunteers, and to assess the frequency with which OCJ defects co-located with BMLs or cartilage defects. Test-retest repeatability was evaluated using kappa statistics. RESULTS Participant characteristics are displayed in table 1. Six out of 9 OA participants (67%) had an OCJ defect in at least one region compared to 0 out of 4 controls (0%). The most commonly involved region was the central medial tibia (4 participants). OCJ defects commonly co-located to BMLs (7 out of 10 OCJ defects, 70%) and cartilage defects (6 out of 10 OCJ defects, 60%). Results are displayed in table 2. Sample images are displayed in figures 1 - 3. The kappa value for test-retest repeatability of OCJ assessment using UTE was 0.83 (95% confidence interval 0.64 to 1). DISCUSSION The appearances of OCJ defects in subjects with OA in vivo are in keeping with abnormalities predicted by cadaveric MR and histology studies(1, 3). The biological plausibility of the findings is enhanced by the frequency of co-location of OCJ damage to other osteochondral pathology (BMLs and cartilage defects). Our findings demonstrate in vivo translation of UTE imaging of the OCJ, and suggest that this is a useful tool for future studies of OA onset and progression. This may include predicting response to intervention, as equine studies have demonstrated that the presence or absence of OCJ damage is an important predictor of response to treatment of cartilage defects(7). Our results demonstrate that UTE imaging of the OCJ is repeatable with kappa values in keeping with 'near-perfect' test-retest repeatability for qualitative assessment(8). Previous in vivo studies have not used age-matched control subjects, therefore it has been unclear whether areas of OCJ damage are related to OA or normal ageing(4). The normal appearance of the OCJ in age-matched control subjects in this study suggests that the OCJ defects are not part of normal ageing, although at present the number of healthy volunteers imaged is small. CONCLUSION In vivo UTE MR imaging of the OCJ is repeatable and demonstrates OCJ defects in subjects with OA. OCJ defects commonly co-locate with other osteochondral pathology

Concurrent and Retrospective Metacognitive Judgements as Feedback in Audience Response Systems: Impact on Performance and Self-Assessment Accuracy

Asking questions in classrooms can produce metacognitive judgements in students about their confidence in being able to answer correctly. In audience response systems (ARSs), these judgements can be elicited and used as additional feedback metrics. This study (n = 79) explores how online concurrent item-by-item judgments (OCJ) and retrospective composite judgments of performance accuracy (RJPA) can enhance students’ performance and self-assessing accuracy (i.e., calibration – as measured by sensitivity, specificity, and absolute accuracy index). In each of eight weeks, the students answered a multiple-choice quiz and had to denote their level of confidence that their answers were correct (OCJ) and estimate their final score (RJPA). The quizzes followed the voting/revoting paradigm according to which students answer all the quiz questions, receive feedback, and answer the same questions again before the correct answers are shown. The students were randomly grouped into two conditions based on the feedback they received in the ARS: the OCJ group (n = 41) received the percentage distribution and peers’ OCJs as feedback metrics, while the RJPA group (n = 38) received the percentage distribution and peers’ RJPAs. Data analysis showed a systemic underconfidence that affected students’ OCJ judgments. As a result, students in the RJPA group scored significantly higher than the ones in the OCJ one, were more accurate in self-assessing in the revoting phase, and felt overall more confident in the revoting phase. The study also discusses the relationship between the two judgments employed and the calibration variability between the two study phases

Breeding Resistance to Butternut Canker Disease

Butternut (Juglans cinerea L.) is being killed throughout its native range by an exotic fungus Ophiognomonia clavigignenti-juglandacearum (Ocj). In recent years, many disease-free trees have been determined to be complex hybrids with an admixture of Japanese walnut (J. ailantifolia). Recently developed molecular and morphological characterizations allow us to accurately identify and separate hybrid and pure butternut progeny. Disease-free-trees, from across butternut’s native range, are the basis of our breeding program in the Central Hardwood Region of the eastern United States. Our first clone banks and seed orchards were grafted and established in the 1990s and 2000s, and are now producing seed for resistance screening. In 2008, we challenged 5-year-old trees from our first two field progeny tests with Ocj. The first test, planted in 2003, had 37 diverse families (n=319). Thirty-two of these seedling families were derived from a grafted orchard of putatively resistant selections. Five additional families were collected from healthy hybrid trees. In early fall of 2008, trees were inoculated with two isolates of Ocj obtained from branch cankers on trees in two locations in Indiana. The trees were scored 8, 12, 20, and 24 months after inoculation for canker incidence and severity. Native butternuts in the adjacent woods provided a source of inoculum whereby natural infections from Ocj began to occur in the third year. Cumulative natural canker incidence and severity were recorded at 5 and 7 years. The second test, planted in 2004, had 12 pure butternut half-sib families collected from a woodlot with: four resistant, four moderately resistant, four susceptible, and one resistant hybrid families (n=213). Resistance ratings were based on the disease status of the mother trees in the stand when the seed was harvested in the fall of 2002. In early fall of 2008, trees were inoculated with the same two isolates of Ocj used in the first test. The trees were scored 8, 12, 20, and 24 months after inoculation for canker incidence and severity. There was no natural infection in the second test. Hybrid butternut families were more resistant to natural infection than the pure butternut families. Eight months after inoculation, canker incidence and severity varied significantly among butternut hybrid families and Ocj isolate, but not among pure butternut families. After 12, 20, and 24 months, canker incidence and severity of pure butternut families changed. By 24 months, hybrid families in general have shown reduced canker expansion and a high level of resistance. Pure butternut families exhibit more variation from highly susceptible to resistant. Year-to-year variation in canker growth suggests that it may take several years to determine the resistance status of butternut with artificial stem inoculations

A critical evaluation of the independence of the Office of the Chief Justice and its role in promoting judicial transformation in South Africa

The legislative supremacy of Parliament has dominated the constitutional law of South Africa for a very long time. In the pre-constitutional era, the judiciary had no power to question the deeds of Parliament. Despite the need for the judiciary to be independent from the two other governmental branches to execute its function effectively, it was surely dependent on them. However, the creation of the Office of the Chief Justice (OCJ) as a separate governmental department by the Constitutional Seventeenth Amendment Act, read together with Superior Court Act, mandated by the requirements of a supreme Constitution (and not Parliament), changed things so that the judiciary is no longer dependent on government for its day-to-day administration. This thesis examines the independence of the OCJ and its role in promoting judicial transformation in the new South Africa.Public, Constitutional and International LawLL. M. (Human Rights Law

Distributed Algorithms for Spectrum Allocation, Power Control, Routing, and Congestion Control in Wireless Networks

We develop distributed algorithms to allocate resources in multi-hop wireless networks with the aim of minimizing total cost. In order to observe the fundamental duplexing constraint that co-located transmitters and receivers cannot operate simultaneously on the same frequency band, we first devise a spectrum allocation scheme that divides the whole spectrum into multiple sub-bands and activates conflict-free links on each sub-band. We show that the minimum number of required sub-bands grows asymptotically at a logarithmic rate with the chromatic number of network connectivity graph. A simple distributed and asynchronous algorithm is developed to feasibly activate links on the available sub-bands. Given a feasible spectrum allocation, we then design node-based distributed algorithms for optimally controlling the transmission powers on active links for each sub-band, jointly with traffic routes and user input rates in response to channel states and traffic demands. We show that under specified conditions, the algorithms asymptotically converge to the optimal operating point.Comment: 14 pages, 5 figures, submitted to IEEE/ACM Transactions on Networkin

Some Gasdynamic Problems in the Flow of Condensing Vapors

Some Gasdynamic Problems in the Flow of Condensing Vapors. The general problem of the flow of a wet vapor, with or without an inert diluent is formulated under the assumption that the liquid phase is finely divided and dispersed throughout the gaseous component in droplets whose radii are nearly constant in any local region. The processes of momentum transfer, heat transfer between phases are assumed to take place according to Stokes law and Nusselt number of unity, respectively. The mass transfer process is treated as diffusion governed in the presence of an inert diluent and kinetic governed for two phases of a pure substance. The physical understanding of such problems, in contrast with those of conventional gas dynamics, rests largely in the role played by the relaxation times or equilibration lengths associated with these three processes. Consequently, both simple and coupled relaxation processes are examined rather carefully by specific examples. Subsequently, the problem of near-equilibrium flow in a nozzle with phase change is solved under the small-slip approximation. The structure of the normal shock in a pure substance is investigated and reveals three rather distinct zones: the gasdynamic shock, the vapor relaxation zone, and the thermal and velocity equilibration zone. The three-dimensional steady flow of the two-phase condensing continuum is formulated according to first order perturbation theory, and the structure of waves in such supersonic flow is examined. Finally, the attenuation of sound in fogs is formulated and solved accounting for the important effects of phase change as well as the viscous damping and heat transfer which have been included in previous analyses