Abstract #1438
Joint Design of Continuous Excitation k-space Trajectory and RF pulse for 3D Tailored Excitation
Hao Sun 1 , Jeffrey A. Fessler 1 , Douglas C. Noll 2 , and Jon-Fredrik Nielsen 2
1
Electrical Engineering and Computer Science,
the University of Michigan, Ann Arbor, MI, United
States,
2
Biomedical
Engineering, the University of Michigan, Ann Arbor, MI,
United States
In 3D tailored RF pulse design, one typically
predetermines a k-space (gradient) trajectory and then
designs the corresponding RF waveforms for a target
excitation pattern. Recently, the KT-points method was
proposed as an approach for jointly designing the
trajectory and RF pulses for 3D flip-angle
homogenization (B1 shimming). KT-points models the 3D
pulse design as a sparse approximation problem and
selects sparse phase encoding locations by either a
greedy approach or a simple inverse Fourier transform
ignoring transmit coil sensitivity and field
inhomogeneity. However, with only a few discrete phase
encoding locations, it is difficult to approximate a
non-smooth target excitation pattern in 3D. Also, it is
relatively inefficient to traverse 3D k-space by
discrete gradient blips with no RF transmission along
those blips. In this work, we extend the KT-points
method to a joint optimization of the continuous k-space
trajectory and the RF waveform by: (1) applying local
minimization to further optimize those KT points, and
(2) efficiently ordering those points and generating a
fast gradient waveform to traverse those points. We
evaluate our proposed joint design with and without
local minimization, and compare them with a recently
proposed continuous nonselective spiral (SPINS)
trajectory for 3D cubic excitation.
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