Adaptive Radiofrequency Shimming in MRI using Reconfigurable Dielectric Materials

• Main Authors: Šiurytė, Paulina, van de Velde, Robert, van Leeuwen, Jasper, Akgun, Omer Can, Brink, Wyger, Weingärtner, Sebastian
• Format: Journal Article
• Language: English
• Published: 02-10-2024
• Subjects: Physics - Applied Physics; Physics - Medical Physics
• DOI: 10.48550/arxiv.2410.01501

Inhomogeneity of the transmitted radiofrequency field B1+ is a major factor
hindering the image quality in Magnetic Resonance Imaging (MRI) at high field
strengths. Here, a novel approach is presented, to locally modulate the B1+
utilizing an array of high permittivity materials with switchable connections.
A 3$\times$3 array of barium titanate suspension elements was constructed, with
two PIN diode-based switchable connectors per element. Electromagnetic
simulations were performed to determine configurations that produce strong B1+
modulation. Remote B1+ field switching was tested in a disk- and and a
torso-shaped phantom at 3T by applying different bias voltages to the PIN
diodes. The attained B1+ modulation was assessed at various switching pattern
positions and various depths within the phantoms. The configuration with the
strongest effect size has produced up to 11% modulation in simulations at 15 mm
depth, with excellent translation properties. The effects were successfully
replicated in phantoms, with a 5 V bias voltage producing up to 11.6$\pm$0.2%
modulation. At the relative depth of the human heart, up to 6% of modulation
was observed in the torso phantom. The presented method may provide a promising
direction for cost-effective, and adaptive B1+ shimming without changes to the
scanner hardware.