Optimization of an 8-Channel Loop-Array Coil for a 7 T MRI System with the Guidance of a Co-Simulation Approach

Minimizing coupling between coil elements is technically challenging in designing large-sized, volume-type phased-array coils for human head imaging at ultrahigh fields, e.g., 7 T. As a widely used decoupling method, the capacitive decoupling method has shown excellent performance for loop array. However, building a multi-channel loop array with capacitive decoupling method is laborious that tuning frequency and matching of one coil element will affect adjacent elements and even next adjacent elements. In this study, we made an 8-channel loop-array transmit/receive radio-frequency coil on a 7 T magnetic resonance imaging system with the guidance of frequency domain three-dimensional electromagnetic and radio-frequency circuit co-simulation. The position of decoupling capacitors was investigated and values of all capacitors were predicted from co-simulation. The co-simulation approach cost about 2 days and the error of the predicted and practical capacitance was <5 %. To demonstrate the accuracy of simulation, we evaluated the simulated and measured S-parameter matrixes and B ₁ ⁺ profiles in a birdcage-like excitation mode on a cylindrical water phantom. In addition, B ₁ ⁺ maps and images of human head were shown with the fabricated coil. To demonstrate the parallel imaging performance of this coil array, GRE images using GRAPPA acceleration with the reduction factor R of 1, 2, 3, and 4 were acquired.     

Operational Research and Formal Education

This paper, which was originally presented at the Second International Working Seminar of the University of Sussex in April 1978, gives an overview of Operational Research as applied to formal education in the United States. It first reviews past work in the field, much of which dates from the mid 1960's, when administrators first turned to O.R. for resolution of education's peculiar crisis situation. From this base, it develops a projection of an attainable state of the science and a proposal for its attainment.     

Characterizations of life distributions from percentile residual lifetimes

Summary An α-percentile residual life function does not uniquely determine a life distribution; however, a continuous life distribution can be uniquely determined by its α-percentile and β-percentile residual life functions if α and β satisfy a certain condition. Two characterizations in terms of percentle residual lifetimes are given for the Beta (1, θ,K), Exponential (λ) and Pareto (θ,K) family of distributions.     

Global Odyssey 2002: International conference on proficiency testing for medical laboratories

Accreditation and Quality Assurance -     

Non-covalent switch for intramolecular energy transfer

The axially coordinated complex of phenylazopyridine and a Zn-porphyrin/free-base porphyrin conjugate provides a switch for intramolecular energy transfer, with reversible complexation/decomplexation as a switching protocol.