Fast Joint Design of RF and Gradient Waveforms for MRI Parallel Excitation
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For past few decades, magnetic resonance imaging (MRI) has been increasingly used for various clinical applications for its excellent contrast on soft tissues. MRI is composed of roughly two sequential procedures: excitation and acquisition. Conventional excitation has been conducted by transmitting a magnetic field in a radio-frequency (RF) with single RF transmission coil. One shortcoming of the single coil transmission is that it is very hard to spatially tailor the RF pulse deposition pattern. This is a significant limitation for multi-dimensional excitation required for inner-volume imaging, signal recovery for BOLD fMRI, and etc. Recently, parallel excitation, simultaneous transmission of multiple RF pulses with multiple coils, has been proposed to overcome this limitation of conventional single coil transmission. However, most of RF pulse design methods proposed so far focused only on the RF pulse optimization, leaving the gradient waveforms unoptimized. In this thesis, we introduce a fast joint optimization scheme for RF pulse and gradient waveforms in parallel excitation to enhance the excitation accuracy. Our algorithm considers an off-resonance effect in the optimization, which was critical in improving the excitation accuracy compared with previous methods that ignored it. We demonstrated the potential advantages our algorithm over previous methods through computer simulations.