Adaptive radiofrequency shimming in MRI using reconfigurable dielectric materials

Abstract

Abstract Inhomogeneity of the transmitted radiofrequency field ( $$B_1^+$$ ) 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 $$B_1^+$$ 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 $$B_1^+$$ modulation. Remote $$B_1^+$$ 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 $$B_1^+$$ 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 $$B_1^+$$ shimming without changes to the scanner hardware.