Improving magnetic resonance imaging with smart and thin metasurfaces

Abstract

Over almost five decades of development and improvement, Magnetic Resonance Imaging (MRI) has become a rich and powerful, non-invasive technique in medical imaging, yet not reaching its physical limits. Technical and physiological restrictions constrain physically feasible developments. A common solution to improve imaging speed and resolution is to use higher field strengths, which also has subtle and potentially harmful implications. However, patient safety is to be considered utterly important at all stages of research and clinical routine. Here we show that dynamic metamaterials are a promising solution to expand the potential of MRI and to overcome some limitations. A thin, smart, non-linear metamaterial is presented that enhances the imaging performance and increases the signal-to-noise ratio in 3T MRI significantly (up to eightfold), whilst the transmit field is not affected due to self-detuning and, thus, patient safety is also assured. This self-detuning works without introducing any additional overhead related to MRI-compatible electronic control components or active (de-)tuning mechanisms. The design paradigm, simulation results, on-bench characterization, and MRI experiments using homogeneous and structural phantoms are described. The suggested single-layer metasurface paves the way for conformal and patient-specific manufacturing, which was not possible before due to typically bulky and rigid metamaterial structures.

Performance Assessment of a Single-Layer Metasurface Resonator for 3 T MRI

“…To verify that all the prototypes detune efficiently during the experiment (in the TX phase), a nominal flipangle sweep was performed while observing the SNR behavior [2]. The results are presented in Figure 6.…”

“…Thus, it becomes challenging to innovate and advance the field in terms of, for example, imaging efficiency. Electromagnetic metamaterials are a promising solution in this respect, since they allow substantial enhancement of the signal-to-noise ratio (SNR) [1,2], which benefits resolution and scanning time. A major drawback is the usually bulky design of the metamaterial structures, putting patient-specific and conformal metasurfaces for versatile applications beyond reach.…”

“…A major drawback is the usually bulky design of the metamaterial structures, putting patient-specific and conformal metasurfaces for versatile applications beyond reach. However, the development of thin (submillimeter) dual-layer metasurfaces [2] overcomes these problems and is the first step toward even more advanced applications. Moreover, smart self-detuning strategies in the transmit phase of MRI (TX) allow patient safety to be taken care of at all times [2,3].…”

“…However, the development of thin (submillimeter) dual-layer metasurfaces [2] overcomes these problems and is the first step toward even more advanced applications. Moreover, smart self-detuning strategies in the transmit phase of MRI (TX) allow patient safety to be taken care of at all times [2,3]. The combination of both thin metasurfaces and inherent self-detuning allows for the most advanced metasurfaces for MRI to date.…”

“…Here we advance the development by proceeding toward single-layer metasurfaces, which can be manufactured in a single step by a state-of-the-art laser etching process. These metasurfaces make use of interdigital capacitors [4], which replace the parallelplate two-layer structures in [2].…”