Multiple gradient echo propeller (MGREP) MRI: Technical development and potential applications

The PROPELLER (Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction) magnetic resonance imaging (MRI) technique has inherent advantages over other fast imaging methods, including robust motion correction, reduced image distortion, and resistance to off-resonance effects. These features make PROPELLER highly desirable for T2*-sensitive imaging, high-resolution diffusion imaging, and many other applications. However, PROPELLER has been predominantly implemented as a fast spin-echo (FSE) technique, which is insensitive to T2* contrast, and requires time-inefficient signal averaging to achieve adequate signal-to-noise ratio (SNR) for many applications. These issues presently constrain the potential clinical utility of FSE-based PROPELLER. ^ In this research, our aim was to extend and enhance the potential applications of PROPELLER MRI by developing a novel multiple gradient echo PROPELLER (MGREP) technique that can overcome the aforementioned limitations. The MGREP pulse sequence was designed to acquire multiple gradient-echo images simultaneously, without any increase in total scan time or RF energy deposition relative to FSE-based PROPELLER. A new parameter was also introduced for direct user-control over gradient echo spacing, to allow variable sensitivity to T2* contrast. In parallel to pulse sequence development, an improved algorithm for motion correction was also developed and evaluated against the established method through extensive simulations. The potential advantages of MGREP over FSE-based PROPELLER were illustrated via three specific applications: (1) quantitative T2* measurement, (2) time-efficient signal averaging, and (3) high-resolution diffusion imaging. Relative to the FSE-PROPELLER method, the MGREP sequence was found to yield quantitative T2* values, increase SNR by ∼40% without any increase in acquisition time or RF energy deposition, and noticeably improve image quality in high-resolution diffusion maps. In addition, the new motion algorithm was found to improve the performance considerably in motion-artifact reduction. ^ Overall, this work demonstrated a number of enhancements and extensions to existing PROPELLER techniques. The new technical capabilities of PROPELLER imaging, developed in this thesis research, are expected to serve as the foundation for further expanding the scope of PROPELLER applications. ^

Intensive Metrics for the Study of the Evolution of Open Source Projects: Case Studies from Apache Software Foundation Projects

Based on the empirical evidence that the ratio of email messages in public mailing lists to versioning system commits has remained relatively constant along the history of the Apache Software Foundation (ASF), this paper has as goal to study what can be inferred from such a metric for projects of the ASF. We have found that the metric seems to be an intensive metric as it is independent of the size of the project, its activity, or the number of developers, and remains relatively independent of the technology or functional area of the project. Our analysis provides evidence that the metric is related to the technical effervescence and popularity of project, and as such can be a good candidate to measure its healthy evolution. Other, similar metrics -like the ratio of developer messages to commits and the ratio of issue tracker messages to commits- are studied for several projects as well, in order to see if they have similar characteristics.

Offshore wind foundation design: some key issues

Despite the growth of the offshore wind industry, there are currently doubts relating to the design of wind facilities in the sea. This paper expounds current, already identified structural uncertainties: problems for soil characterization and transition piece (TP) design. This document also introduces new doubts or issues to be researched in the near future in this field (wave theory, scour process, wave load actions, scale difficulty, etc.), not as yet identified due to the scarce experience in the offshore wind industry. With this in mind, technical offshore wind standards related to foundation design have been reviewed.

Validation of truck handling simulation results. Volume II: technical report. Final report.

Federal Highway Administration, Washington, D.C.

A chart book of indicators of scientific & technical communication in the United States /

"Prepared by Donald W. King, Barbara L. Wood, and Charles G. Schueller.

Goods transportation in urban areas : proceedings of the Engineering Foundation Conference, Sea Island, Georgia, December 4-9, 1977 /

Report no. FHWA-32-26-008.

Survey and analysis of specialized science information services in the United States to National Science Foundation /

"Contract NSF-C149."

Federal scientific and technical personnel : detailed statistical tables.

"NSF 81-309."

Goods transportation in urban areas; proceedings of the Engineering Foundation Conference, held at South Berwick, Maine, on August 5-10, 1973.

Inserted Technical report documentation page disignates Gordon P. Fisher as "editor."

Technology and the neurologically handicapped : a conference cosponsored by the National Aeronautics and Space Administration and the United Cerebral Palsy Foundation, and held at Ames Research Center, Moffett Field, California, September 8-10, 1971

Includes bibliographies

Research in nonlinear structural and solid mechanics : keynote address and panel discussion presented at a symposium sponsored by NASA Langley Research Center, Hampton, Virginia, and the George Washington University, Washington, D.C., in cooperation with the National Science Foundation, the American Society of Civil Engineers, and the American Society of Mechanical Engineers, and held at Washington, D.C., October 6-8, 1980 /

Includes bibliographical references.

Progress in scientific and technical communications ; annual report.

"COSATI."

Federal scientific and technical communication activities ; progress report.

Vols. for issued as U.S. National Science Foundation. NSF.

Projected response of the science, engineering, and technical labor market to defense and nondefense needs : 1982-84 [i.e. 87]

"NSF 84-304."

Nonconventional Technical Information Systems in Current Use; Report

Mode of access: Internet.