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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