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Abstract #2753

Design Optimizations Regarding Eddy Currents of a High Performance Head Gradient Coil

Silke M. Lechner-Greite1, Jean-Baptiste Mathieu2, Seung-Kyun Lee3, Bruce C. Amm4, Thomas K. Foo5, John F. Schenck6, Matt A. Bernstein7, John Huston7

1Diagnostics and Biomedical Technologies, GE Global Research Europe, Garching n. Munich, Germany; 2Electromagnetics & Superconductivity Laboratory, GE Global Research Niskayuna, Albany, NY, United States; 3MRI Laboratory, GE Global Research Niskayuna, Albany, NY, United States; 4Biomedical and Electronic Systems Laboratory, GE Global Research Niskayuna, Albany, NY, United States; 5Diagnostics and Biomedical Technologies, GE Global Research Niskayuna, Albany, NY, United States; 6MRI Technologies & Systems, GE Global Research Niskayuna, Albany, NY, United States; 7Mayo Clinic, Rochester, MN, United States

We report on the design and eddy current simulation of a head-only shielded gradient coil prototype consisting of asymmetric transverse gradients and a symmetric axial gradient. Eddy currents induced in a conductive cylinder surrounding the gradient coil were evaluated during prototyping stage using eddy image calculation and certain higher-order eddy currents were suppressed by design to ensure good image quality for applications like diffusion weighted imaging. Finite element simulations in static, frequency, and transient domain confirmed the level of higher-order harmonic field distortion predicted by eddy current image computation, and revealed the frequency content, amplitude, and time evolution of the eddy current field in the imaging field of view. The spatial linearity of the gradient field was found to be significantly affected by the time-dependent higher-order harmonic eddy current terms.

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Keywords

accurately achieve achieved agreement allow amplitude applied assessment assuming asymmetric axes behavior better biomedical blocks capability coil coils comparable components conductivity conductor constant constants constraint constraints cryostat curve decay dedicated described design designed desired developed diagnostics diffusion directly distorted domain eddy element establishment evaluated evaluation excellent expressed extracted field finite fitted fitting focus forces frequency function generated global gradient gradients harmonic harmonics head highly horizontal ideal illustrate illustration impact inclusion induced influence insight john king laboratory least linear linearity magnet maps maxwell minimization mode model modeling must nicely nominal nonlinearity optimal optimization partly percentage perfect performance plots prediction predictions produced prototype pulse pulsed quality ramp reduced refined regarding report residual respectively response responses sampling shield simulate simulating simulation simulations slew specialty specifications speed spherical static steps stream strength strengths strong structures submitted subsequent system systems target targeted technologies temporal term terms thermal tightened tools transferred transient trapezoidal utilized validated view whole