Meeting Banner
Abstract #4265

Large Tip Angle KT-Points Based on a Linearization of the Bloch Equations

Florent Eggenschwiler1, Rolf Gruetter2, Jos P. Marques3

1EPFL, Laboratory for Functional and Metabolic Imaging, Lausanne, Vaud, Switzerland; 2Universities of Geneva and Lausanne, cole Polytechnique Fdrale de Lausanne, Lausanne, Vaud, Switzerland; 3University of Lausanne, Department of Radiology, Lausanne, Vaud, Switzerland

This work presents a new approach for designing high tip angle kT-point pulses based on a linearization of the Bloch equations and usage of symbolic notation to accelerate the computation when the optimization has to be performed for large number of pixels. Based on the differentiation of the analytic form of the Bloch equations, the kT-point weights and positions were iteratively optimized in order to converge towards a targeted distribution of the magnetization across the brain. The validity of the method was demonstrated by designing high tip angle kT-points excitation and refocusing pulses.

Keywords

adapted although amplitude another applied approximation around best better brain closer coefficients combining components computation considered consists corresponds criterion defined degree describing design designed designing desirable displays distribution domain done either equations evaluated excitation expensive extended extension faster field form formalism foundations freedom full functional functions good gradient gradients halved hence highly histograms homogeneous homogenization imaginary improvement in vivo increment inhomogeneous initial inside inversion iteration iterations iterative iteratively laboratory likely linear linked local loops made magnetization making maps marques matrix metabolic methodology notation offered operations optimal optimization optimizations optimizing parallel part pixels position positions principle problem procedure profile profiles proposed pseudo pulse pulses radiology reached real reducing refocusing regime regularization remaining repeated resources respectively rotation seeks several similarly since solo solution spin standalone starting step steps stopped stopping stored strengths stringent subset succession symbolic symmetric symmetrically system target term terms throughout trajectory transfer transverse turbo updated usage validity variable vector waveforms weightings written