Recent Advances and Challenges in the Development of Radiofrequency HTS Coil for MRI

Aimé Labbé,Luc Darrasse,Cornelis J Van Der Beek,Javier Briatico,Gilles Authelet,Bertrand Baudouy,Marie Poirier-Quinot

doi:10.3389/fphy.2021.705438

Abstract

Radiofrequency (RF) coils fashioned from high-temperature superconductor (HTS) have the potential to increase the sensitivity of the magnetic resonance imaging (MRI) experiment by more than a dozen times compared to conventional copper coils. Progress, however, has been slow due to a series of technological hurdles. In this article, we present the developments that recently led to new perspectives for HTS coil in MRI, and challenges that still need to be solved. First, we recall the motivations for the implementations of HTS coils in MRI by presenting the limits of cooled copper coil technology, such as the anomalous skin effect limiting the decrease of the electric resistance of normal conductors at low temperature. Then, we address the progress made in the development of MRI compatible cryostats. New commercially available low-noise pulsed-tube cryocoolers and new materials removed the need for liquid nitrogen-based systems, allowing the design of cryogen-free and more user-friendly cryostats. Another recent advance was the understanding of how to mitigate the imaging artifacts induced by HTS diamagnetism through field cooling or temperature control of the HTS coil. Furthermore, artifacts can also originate from the RF field coupling between the transmission coil and the HTS reception coil. Here, we present the results of an experiment implementing a decoupling strategy exploiting nonlinearities in the electric response of HTS materials. Finally, we discuss the potential applications of HTS coils in bio-imaging and its prospects for further improvements. These include making the technology more user-friendly, implementing the HTS coils as coil arrays, and proposing solutions for the ongoing issue of decoupling. HTS coil still faces several challenges ahead, but the significant increase in sensitivity it offers lends it the prospect of being ultimately disruptive.

Highlights

The discovery of high-temperature superconductivity (HTS) by [1], paved the way for the application of superconductor-based technologies at temperatures above that of boiling nitrogen
The vanishing electric resistance of the superconducting Magnetic Resonance Imaging (MRI) coil brings electric noise levels within reach that are unachievable with more traditional copper coils, even if the latter are cooled to much lower temperatures than the HTS coil; typically, the signal-tonoise ratio (SNR) can be increased more than a dozen times [3]
We reviewed some of the challenges and recent advances made in the implementation of HTS coil in MRI

Summary

INTRODUCTION

The discovery of high-temperature superconductivity (HTS) by [1], paved the way for the application of superconductor-based technologies at temperatures above that of boiling nitrogen. The quality factor Q of HTS coils depends on the power of the incident RF magnetic signal Their Q of a few thousand during reception (low power stage), FIGURE 4 | Schematic drawing of the interior of the dedicated cryostat used in Setup 1.The VNA is connected to a measurement probe inductively coupled to the HTS coil, which is secured on a cold finger. In a second step (Setup 2), we present this decoupling approach implemented in an MRI environment (Figure 2), allowing the material to pass from a zero-resistance state to a dissipative state during transmission [49] In both setups, the experiments were conducted with a resonating (ω 63.5 MHz at 70 K) HTS surface coil of identical design as the one described in the previous section [5]. This can be explained by the temperature, field, and field-orientation dependence of the critical current density of the HTS material, as studied by [45], in comparable conditions

DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT