arXiv subjects

Rita Schmidt

Publications and source records attributed to Rita Schmidt.

3 recordsLinked to original sources

arXiv2025

Modular Metamaterials for Adaptable MRI Signal Control: Combining Dipole Arrays with Hexagon-based Artificial Dielectrics

Emerging concepts of metamaterials for MRI offer improved image quality through enhanced RF field control. However, current designs are often limited by bulky configurations, dielectric losses, and limited adaptability. Patient-specific optimization - essential for improving field homogeneity, boosting local SNR, and addressing anatomical variability - requires redesigning each setup. To overcome these limitations, we introduce a hexagonally-packed artificial dielectric, free of any lumped-elements, capable of achieving a wide range of high relative permittivities (30-1400) suitable for clinical and ultra-high-field MRI. We identify multilayered and in-plane-shifted hexagonal configurations that support compact, modular layouts. Furthermore, we combine these artificial dielectrics with dipole arrays to create a modular system for adaptable signal enhancement, tuned via electric and magnetic dipole modes by adjusting the length of conductive strips. In-vivo 7T MRI results demonstrate enhanced field control and high-resolution imaging. This lightweight, flexible, and modular platform enables patient-specific RF field shaping, thus opening up new avenues for personalized and adaptable MRI technology.

physics.med-ph↗

arXiv2025

Timing is everything: How subtle timing changes in MRI echo planar imaging can significantly alter mechanical vibrations and sound level

Modern MRI relies on the well-established Echo-Planar-Imaging (EPI) method for fast acquisition. EPI is the workhorse of diffusion and functional MRI in neuroscience as well as of many dynamic applications for clinical body imaging. Its speed stems from rapidly switching currents through the gradient coils responsible for spatial encoding. These quick changes, within a strong static magnetic field induce Lorentz forces that generate mechanical vibrations, leading to the loud, characteristic MRI noise. This acoustic noise is already a significant concern in standard clinical scanners, requiring hearing protection and risking image degradation or even hardware strain. In ultra-high-field systems, the issue is exacerbated due to stronger Lorentz forces. In this study, we introduce a novel model that characterizes the acoustic spectrum for a given EPI scan. The spectrum results from interference between multiple identical periods of alternating currents, making the relative timing between them a key factor. We show that even subtle timing changes significantly alter the sound level. Scans of either high spatial resolution or high temporal resolution, on clinical 7T and investigational 10.5T human scanners, corroborated the model and its predicted acoustics spectra. Acoustic energy changes of up to 47-fold were reached in close to mechanical resonances and up to 5-fold in other regions. Intriguingly, under certain conditions, doubling the acquisitions per unit time actually reduced the minimal acoustic energy two-fold. Not less important, ghosting-artifacts exhibit strong dependence on the scan's acoustic characteristics and the benefit of subtle time delays of internal correction-acquisitions (navigators) is also demonstrated.

physics.med-ph↗

arXiv2016

Flexible and compact hybrid metasurfaces for enhanced ultra high field in vivo magnetic resonance imaging

Developments in metamaterials and related structures such as metasurfaces have opened up new possibilities in designing materials and devices with unique properties. The main progress related to electromagnetic waves applications was done in optical and microwave spectra. Here we report about a new hybrid metasurface structure, comprising a two-dimensional metamaterial surface and a very high permittivity dielectric substrate that was designed to enhance the performance of an ultra-high field MRI scanner. This new flexible and compact resonant structure is the first one which can be integrated into a multi-element close-fitting receive coil array used for all clinical MRI. We successfully demonstrated the operation of the metasurface in acquiring vivo human brain images and spectra with enhanced local sensitivity on a commercial 7 Tesla system. These experimental findings prove the feasibility of real clinical applications of metasurfaces in MRI.

physics.med-ph↗