Imperfect spoiling in variable flip angle T1 mapping at 7T: Quantifying and minimizing impact

PURPOSE: The variable flip angle (VFA) approach to T1 mapping assumes perfectly spoiled transverse magnetisation at the end of each repetition time (TR). Despite radiofrequency (RF) and gradient spoiling, this condition is rarely met, leading to erroneous T1 estimates ( T 1 app ). Theoretical corrections can be applied but make assumptions about tissue properties, for example, a global T2 time. Here, we investigate the effect of imperfect spoiling at 7T and the interaction between the RF and gradient spoiling conditions, additionally accounting for diffusion. We provide guidance on the optimal approach to maximise the accuracy of the T1 estimate in the context of 3D multi-echo acquisitions. METHODS: The impact of the spoiling regime was investigated through numerical simulations, phantom and in vivo experiments. RESULTS: The predicted dependence of T 1 app on tissue properties, system settings, and spoiling conditions was observed in both phantom and in vivo experiments. Diffusion effects modulated the dependence of T 1 app on both B 1 + efficiency and T2 times. CONCLUSION: Error in T 1 app can be minimized by using an RF spoiling increment and gradient spoiler moment combination that minimizes T2 -dependence and safeguards image quality. Although the diffusion effect was comparatively small at 7T, correction factors accounting for this effect are recommended

Alien Registration- Corbin, Marie N. (Van Buren, Aroostook County)

https://digitalmaine.com/alien_docs/32254/thumbnail.jp

Impact-induced acceleration by obstacles

We explore a surprising phenomenon in which an obstruction accelerates, rather than decelerates, a moving flexible object. It has been claimed that the right kind of discrete chain falling onto a table falls \emph{faster} than a free-falling body. We confirm and quantify this effect, reveal its complicated dependence on angle of incidence, and identify multiple operative mechanisms. Prior theories for direct impact onto flat surfaces, which involve a single constitutive parameter, match our data well if we account for a characteristic delay length that must impinge before the onset of excess acceleration. Our measurements provide a robust determination of this parameter. This supports the possibility of modeling such discrete structures as continuous bodies with a complicated constitutive law of impact that includes angle of incidence as an input.Comment: small changes and corrections, added reference

A search for HI in some peculiar faint dwarf galaxies

We present a deep Giant Metrewave Radio Telescope (GMRT) search for HI 21 cm emission from three dwarf galaxies, viz. POX 186, SC 24 and KKR 25. Based, in part, on previous single dish HI observations, these galaxies have been classified as a BCD, a dwarf irregular and a transition galaxy respectively. However, in conflict with previous single dish detections, we do not detect HI in SC 24 or KKR 25. We suggest that the previous single dish measurements were probably confused with the local galactic emission. In the case of POX 186, we confirm the previous non detection of HI but with substantially improved limits on its HI mass. Our derived upper limits on the HI mass of SC 24 and KKR 25 are similar to the typical HI mass limit for dwarf spheroidal galaxies, whereas in the case of POX 186, we find that its gas content is somewhat smaller than is typical of BCD galaxies.Comment: Accepted for publication in MNRA

A comparison of sensitivity-specificity imputation, direct imputation and fully Bayesian analysis to adjust for exposure misclassification when validation data are unavailable.

: Measurement error is an important source of bias in epidemiological studies. We illustrate three approaches to sensitivity analysis for the effect of measurement error: imputation of the 'true' exposure based on specifying the sensitivity and specificity of the measured exposure (SS); direct imputation (DI) using a regression model for the predictive values; and adjustment based on a fully Bayesian analysis. : We deliberately misclassify smoking status in data from a case-control study of lung cancer. We then implement the SS and DI methods using fixed-parameter (FBA) and probabilistic (PBA) bias analyses, and Bayesian analysis using the Markov-Chain Monte-Carlo program WinBUGS to show how well each recovers the original association. : The 'true' smoking-lung cancer odds ratio (OR), adjusted for sex in the original dataset, was OR = 8.18 [95% confidence limits (CL): 5.86, 11.43]; after misclassification, it decreased to OR = 3.08 (nominal 95% CL: 2.40, 3.96). The adjusted point estimates from all three approaches were always closer to the 'true' OR than the OR estimated from the unadjusted misclassified smoking data, and the adjusted interval estimates were always wider than the unadjusted interval estimate. When imputed misclassification parameters departed much from the actual misclassification, the 'true' OR was often omitted in the FBA intervals whereas it was always included in the PBA and Bayesian intervals. : These results illustrate how PBA and Bayesian analyses can be used to better account for uncertainty and bias due to measurement error.<br/

Detecting the Cosmic Gravitational Wave Background with the Big Bang Observer

The detection of the Cosmic Microwave Background Radiation (CMB) was one of the most important cosmological discoveries of the last century. With the development of interferometric gravitational wave detectors, we may be in a position to detect the gravitational equivalent of the CMB in this century. The Cosmic Gravitational Background (CGB) is likely to be isotropic and stochastic, making it difficult to distinguish from instrument noise. The contribution from the CGB can be isolated by cross-correlating the signals from two or more independent detectors. Here we extend previous studies that considered the cross-correlation of two Michelson channels by calculating the optimal signal to noise ratio that can be achieved by combining the full set of interferometry variables that are available with a six link triangular interferometer. In contrast to the two channel case, we find that the relative orientation of a pair of coplanar detectors does not affect the signal to noise ratio. We apply our results to the detector design described in the Big Bang Observer (BBO) mission concept study and find that BBO could detect a background with $\Omega_{gw} > 2.2 \times 10^{-17}$.Comment: 15 pages, 12 Figure

Mitigating the impact of flip angle and orientation dependence in single compartment R2* estimates via 2-pool modeling

Purpose: The effective transverse relaxation rate ( R∗2 ) is influenced by biological features that make it a useful means of probing brain microstructure. However, confounding factors such as dependence on flip angle (α) and fiber orientation with respect to the main field ( θ ) complicate interpretation. The α- and θ -dependence stem from the existence of multiple sub-voxel micro-environments (e.g., myelin and non-myelin water compartments). Ordinarily, it is challenging to quantify these sub-compartments; therefore, neuroscientific studies commonly make the simplifying assumption of a mono-exponential decay obtaining a single R∗2 estimate per voxel. In this work, we investigated how the multi-compartment nature of tissue microstructure affects single compartment R∗2 estimates. Methods: We used 2-pool (myelin and non-myelin water) simulations to characterize the bias in single compartment R∗2 estimates. Based on our numeric observations, we introduced a linear model that partitions R∗2 into α-dependent and α-independent components and validated this in vivo at 7T. We investigated the dependence of both components on the sub-compartment properties and assessed their robustness, orientation dependence, and reproducibility empirically. Results: R∗2 increased with myelin water fraction and residency time leading to a linear dependence on α. We observed excellent agreement between our numeric and empirical results. Furthermore, the α-independent component of the proposed linear model was robust to the choice of α and reduced dependence on fiber orientation, although it suffered from marginally higher noise sensitivity. Conclusion: We have demonstrated and validated a simple approach that mitigates flip angle and orientation biases in single-compartment R∗2 estimates

"If We Want to Get Men in, Then We Need to Ask Men What They Want": Pathways to Effective Health Programing for Men.

In Ireland, men’s health is becoming a priority. In line with global trends, indicators of poor mental health (including rates of depression and suicide) are increasing alongside rates of unemployment and social isolation. Despite the growing awareness of men’s health as a national priority, and development of the first National Men’s Health Policy in the world, there is still a concern about men’s non-engagement with health services. Health and community services often struggle to appropriately accommodate men, and men commonly avoid health spaces. A growing body of literature suggests that a persistent lack of support or resources for service providers contributes to their inability to identify and meet men’s unique health needs. This study aims to provide further insight into the ways in which this gap between men and health services can be closed. Semi-structured, qualitative interviews were conducted with nine project partners (n=9) of a successful men’s health program in Dublin. Interviews captured reflections on what processes or strategies contribute to effective men’s health programs. Findings suggest that gender-specific strategies – especially related to community- engagement and capacity building - are necessary in creating health programs that both promote men’s health and enable men to safely and comfortably participate. Moreover, including men in all aspects of the planning stages helps to ensure that programs are accessible and acceptable for men. It is envisaged that these findings will be operationalized into a user-driven resource to illustrate evidence-informed strategies and guiding principles that could be used by practitioners hoping to engage with me

Conceptualizing cultures of violence and cultural change

The historiography of violence has undergone a distinct cultural turn as attention has shifted from examining violence as a clearly defined (and countable) social problem to analysing its historically defined 'social meaning'. Nevertheless, the precise nature of the relationship between 'violence' and 'culture' is still being established. How are 'cultures of violence' formed? What impact do they have on violent behaviour? How do they change? This essay examines some of the conceptual aspects of the relationship between culture and violence. It brings together empirical research into nineteenth-century England with recent research results from other European contexts to examine three aspects of the relationship between culture and violence. These are organised under the labels 'seeing violence', 'identifying the violent' and 'changing violence'. Within a particular society, narratives regarding particular kinds of behaviour shape cultural attitudes. The notion 'violence' is thus defined in relation to physically aggressive acts as well as by being connected to other kinds of attitudes and contexts. As a result, the boundaries between physical aggression which is legitimate and that which is illegitimate (and thus 'violence') are set. Once 'violence' is defined, particular cultures form ideas about who is responsible for it: reactions to violence become associated with social arrangements such as class and gender as well as to attitudes toward the self. Finally, cultures of violence make efforts to tame or eradicate illegitimate forms of physical aggression. This process is not only connected to the development of new forms of power (e.g., new policing or punishment strategies) but also to less tangible cultural influences which aim at changing the behaviour defined as violence (in particular among the social groups identified as violent). Even if successful, this three-tiered process of seeing violence, identifying the violent and changing violence continues anew, emphasising the ways that cultures of violence develop through a continuous process of reevaluation and reinvention