Adaptive radiofrequency shimming in MRI using reconfigurable dielectric materials.

Abstract

Inhomogeneity of the transmitted radiofrequency field ([Formula: see text]) 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 [Formula: see text] utilizing an array of high permittivity materials with switchable connections. A 3×3 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 [Formula: see text] modulation. Remote [Formula: see text] field switching was tested in a disk- and a torso-shaped phantom at 3T by applying different bias voltages to the PIN diodes. The attained [Formula: see text] 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±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 [Formula: see text] shimming without changes to the scanner hardware.