ELECTROMAGNETIC SIMULATION OF PARALLEL TRANSMIT RADIOFREQUENCY COILS AND HIGH PERMITTIVITY MATERIALS USING CIRCUIT-SPATIAL OPTIMIZATION WITH VIRTUAL OBSERVATION POINTS

Description

<p>The recent FDA regulatory clearance
for the 7 tesla Magnetic Resonance Imaging (MRI) system has led to increased
interest in clinical ultra-high field (UHF) applications. However, to robustly
achieve the expected increase in signal-to-noise ratio (SNR) at UHF, the
radiofrequency (RF) challenges need to be met, namely, problems with higher RF
power, worse <i>B₁⁺</i> inhomogeneity (signal voids) and increased
tissue dielectric properties at higher frequency, all of which usually results
in increased specific absorption rate (SAR). The parallel transmission (pTx)
techniques are generally accepted as a realistic solution, providing
improvement in the <i>B₁⁺</i> homogeneity with good RF efficiency while
reducing peak local SAR. We designed a hybrid circuit-spatial
domain optimization to accelerate the design of a double row pTx head coil.
The method predicted consistent coil scattering parameters, component values
and <i>B₁⁺</i> field. RF shimming of the calculated field
maps matched in vivo performance. To further
increase the <i>B₁⁺</i> homogeneity in tissue, we added high dielectric material (HPM) pads
near the coil, as the displacement currents in the HPM induced secondary <i>B₁⁺</i> in tissue. This raises a RF safety question
of how to monitor millions of local SAR (complex valued Q-matrix) in the tissue
voxels, for any weightings (forward voltages) applied to the pTx system. We implemented
VOPs based on singular value decomposition to compress the Q-matrices with a
compression ratio >100, effectively monitoring the maximum peak local SAR
values at given weighting amplitudes.</p>

Links & Downloads

1. 10.25394/pgs.12749633.v1

Tags

Biomechanical Engineering

MRI

RF Coil

EM simulation

pTx

Additional Fields

Identifer	oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12749633
Date	04 August 2020
Creators	Xin Li (9193727)
Source Sets	Purdue University
Detected Language	English
Type	Text, Thesis
Relation	https://figshare.com/articles/thesis/ELECTROMAGNETIC_SIMULATION_OF_PARALLEL_TRANSMIT_RADIOFREQUENCY_COILS_AND_HIGH_PERMITTIVITY_MATERIALS_USING_CIRCUIT-SPATIAL_OPTIMIZATION_WITH_VIRTUAL_OBSERVATION_POINTS/12749633