Respiratory organ motion in interventional MRI : tracking, guiding and modeling

Respiratory organ motion is one of the major challenges in interventional MRI, particularly in interventions with therapeutic ultrasound in the abdominal region. High-intensity focused ultrasound found an application in interventional MRI for noninvasive treatments of different abnormalities. In order to guide surgical and treatment interventions, organ motion imaging and modeling is commonly required before a treatment start. Accurate tracking of organ motion during various interventional MRI procedures is prerequisite for a successful outcome and safe therapy. In this thesis, an attempt has been made to develop approaches using focused ultrasound which could be used in future clinically for the treatment of abdominal organs, such as the liver and the kidney. Two distinct methods have been presented with its ex vivo and in vivo treatment results. In the first method, an MR-based pencil-beam navigator has been used to track organ motion and provide the motion information for acoustic focal point steering, while in the second approach a hybrid imaging using both ultrasound and magnetic resonance imaging was combined for advanced guiding capabilities. Organ motion modeling and four-dimensional imaging of organ motion is increasingly required before the surgical interventions. However, due to the current safety limitations and hardware restrictions, the MR acquisition of a time-resolved sequence of volumetric images is not possible with high temporal and spatial resolution. A novel multislice acquisition scheme that is based on a two-dimensional navigator, instead of a commonly used pencil-beam navigator, was devised to acquire the data slices and the corresponding navigator simultaneously using a CAIPIRINHA parallel imaging method. The acquisition duration for four-dimensional dataset sampling is reduced compared to the existing approaches, while the image contrast and quality are improved as well. Tracking respiratory organ motion is required in interventional procedures and during MR imaging of moving organs. An MR-based navigator is commonly used, however, it is usually associated with image artifacts, such as signal voids. Spectrally selective navigators can come in handy in cases where the imaging organ is surrounding with an adipose tissue, because it can provide an indirect measure of organ motion. A novel spectrally selective navigator based on a crossed-pair navigator has been developed. Experiments show the advantages of the application of this novel navigator for the volumetric imaging of the liver in vivo, where this navigator was used to gate the gradient-recalled echo sequence

Implications of Being a Highly Rated Organization: Evidence from Four-Star Rated Nonprofits

This study examines a group of nonprofits rated four stars by Charity Navigator. The purpose is to determine whether this select group of charities exhibits characteristics associated with top charitable organizations, or whether the four-star rating achieved is limited to the more narrow financial metrics employed in the methodology utilized by Charity Navigator. This study finds that organizations rated four stars by Charity Navigator show a lower level of excess cash holdings, report a lower level of compensation expenses and exhibit lower sensitivity of compensation to performance. Financially, these organizations are less vulnerable than their lower rated peers. The results from this study shed light on the continuing debate of the effectiveness of rating agencies to accurately identify top performing charitable organizations

Temporal Interpolation via Motion Field Prediction

Navigated 2D multi-slice dynamic Magnetic Resonance (MR) imaging enables high contrast 4D MR imaging during free breathing and provides in-vivo observations for treatment planning and guidance. Navigator slices are vital for retrospective stacking of 2D data slices in this method. However, they also prolong the acquisition sessions. Temporal interpolation of navigator slices an be used to reduce the number of navigator acquisitions without degrading specificity in stacking. In this work, we propose a convolutional neural network (CNN) based method for temporal interpolation via motion field prediction. The proposed formulation incorporates the prior knowledge that a motion field underlies changes in the image intensities over time. Previous approaches that interpolate directly in the intensity space are prone to produce blurry images or even remove structures in the images. Our method avoids such problems and faithfully preserves the information in the image. Further, an important advantage of our formulation is that it provides an unsupervised estimation of bi-directional motion fields. We show that these motion fields can be used to halve the number of registrations required during 4D reconstruction, thus substantially reducing the reconstruction time.Comment: Submitted to 1st Conference on Medical Imaging with Deep Learning (MIDL 2018), Amsterdam, The Netherland

An Analysis of Some Refractive Error Trends in US Air Force Pilots and Navigators

Refractive error trends with age in US Air Force pilots and navigator

Enabling collaboration in virtual reality navigators

In this paper we characterize a feature superset for Collaborative Virtual Reality Environments (CVRE), and derive a component framework to transform stand-alone VR navigators into full-fledged multithreaded collaborative environments. The contributions of our approach rely on a cost-effective and extensible technique for loading software components into separate POSIX threads for rendering, user interaction and network communications, and adding a top layer for managing session collaboration. The framework recasts a VR navigator under a distributed peer-to-peer topology for scene and object sharing, using callback hooks for broadcasting remote events and multicamera perspective sharing with avatar interaction. We validate the framework by applying it to our own ALICE VR Navigator. Experimental results show that our approach has good performance in the collaborative inspection of complex models.Postprint (published version

Examining the Social Security Tribunal’s Navigator Service: Access to Administrative Justice for Marginalized Communities

An accessible MS Word version of this document is available for download at the bottom of this screen under Additional files. This report provides the findings, analysis and recommendations of a research study conducted on the federal Social Security Tribunal’s Navigator Service (SST Navigator Service). The SST Navigator Service was established in 2019 for tribunal users without a professional representative. The study examines the use of the Navigator Service for Canada Pension Plan–Disability (CPP–Disability) appeals heard by the Income Security - General Division of the Social Security Tribunal. This research study focuses on access to administrative justice on the ground. It examines how the innovative SST Navigator Service facilitates access to CPP disability benefit decision-making as well as the ways that the Navigator Service could be improved. As part of its focus, the study examined how well the Navigator Service supports users from marginalized communities. The SST serves users who are often at the intersections of being people with disabilities and people who live with low income. Statistically, a significant proportion of people who live with low income in Canada are also women, immigrants and/or visible minorities. The SST Navigator Service therefore presents an opportunity to consider how individuals from these and other marginalized communities are experiencing the system and how the service may be helpfully improved. Through 36 semi-structured interviews and documentary analysis, the researchers considered the perspectives of former appellants who used the Navigator Service and received at least one tribunal decision between the Service’s inception in November, 2019 and April, 2021. They also spoke with the navigators and, for context, gathered information from relevant government officials involved in the design, implementation and running of the Navigator Service. In addition to findings about user experiences and navigator roles, the report provides recommendations to maintain and strengthen the SST Navigator Service. It concludes that the SST Navigator Service is an innovation that enhances access to justice. Navigator services may be beneficially adopted by other administrative tribunals at the federal level in Canada, and in the administrative justice systems of the provinces and territories. Navigator services may also be beneficial in jurisdictions beyond Canada. Ce rapport est également disponible en francais

Cancer-related electronic support groups as navigation-aids: Overcoming geographic barriers

Cancer-related electronic support groups (ESGs) may be regarded as a complement to face-to-face groups when the latter are available, and as an alternative when they are not. Advantages over face-to-face groups include an absence of barriers imposed by geographic location, opportunities for anonymity that permit sensitive issues to be discussed, and opportunities to find peers online. ESGs can be especially valuable as navigation aids for those trying to find a way through the healthcare system and as a guide to the cancer journey. Outcome indicators that could be used to evaluate the quality of ESGs as navigation aids need to be developed and tested. Conceptual models for the navigator role, such as the Facilitating Navigator Model, are appropriate for ESGs designed specifically for research purposes. A Shared or Tacit Model may be more appropriate for unmoderated ESGs. Both conceptual models raise issues in Internet research ethics that need to be addres