SQUID-based ultralow-field MRI of a hyperpolarized material using signal amplification by reversible exchange

Seong-Joo Lee,Keunhong Jeong,Jeong Hyun Shim,Sein Min,Heelim Chae,Sung Keon Namgoong,Kiwoong Kim,Hyun Joon Lee

doi:10.1038/s41598-019-48827-5

Abstract

The signal amplification by reversible exchange (SABRE) technique is a very promising method for increasing magnetic resonance (MR) signals. SABRE can play a particularly large role in studies with a low or ultralow magnetic field because they suffer from a low signal-to-noise ratio. In this work, we conducted real-time superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR)/magnetic resonance imaging (MRI) studies in a microtesla-range magnetic field using the SABRE technique after designing a bubble-separated phantom. A maximum enhancement of 2658 for 1H was obtained for pyridine in the SABRE-NMR experiment. A clear SABRE-enhanced MR image of the bubble-separated phantom, in which the para-hydrogen gas was bubbling at only the margin, was successfully obtained at 34.3 μT. The results show that SABRE can be successfully incorporated into an ultralow-field MRI system, which enables new SQUID-based MRI applications. SABRE can shorten the MRI operation time by more than 6 orders of magnitude and establish a firm basis for future low-field MRI applications.

Highlights

Magnetic resonance imaging (MRI) is usually carried out in a strong magnetic field because of the Zeeman effect
The challenge arises from the fact that p-H2-derived 1H nuclear magnetic resonance (NMR) signals often have an anti-phase character, which results in significant signal cancellation if resonances are not resolved
An enhancement factor on the order of a few thousands in real-time NMR/magnetic resonance imaging (MRI) was achieved in the ultralow field, even though the actual level of polarization was on the order of 0.00007%; this value was estimated from the equation ESABRE × tanh(γħBp/2kBT), in which γ is the gyromagnetic ratio of a proton, T is the temperature, and ħ and kB are Planck’s constant and the Boltzmann constant, respectively

Summary

Introduction

Magnetic resonance imaging (MRI) is usually carried out in a strong magnetic field because of the Zeeman effect. They suggested that the addition of H2 molecules enriched in the para-state can result in the enhancement in NMR signals This method was initially called para-hydrogen and synthesis allows dramatically enhanced nuclear alignment (PASADENA) and was later named para-hydrogen induced polarization (PHIP)[10]. Another hyperpolarization technique, called signal amplification by reversible exchange (SABRE), which was developed recently, is considered a significant extension of PHIP11. To obtain a good MR image in SQUID-based microtesla MRI, a pre-polarization field (Bp) is required before the MR signal from the sample is detected. The most well-known way of achieved hyperpolarization, DNP, which is used to transfer polarization from electrons to nuclei, was harnessed to obtain a high-contrast microtesla MR image[18,22]. An enhancement factor of more than 2650 and a clear SABRE-derived 1H MR image of the phantom were obtained with 8 mT Bp at 34.3 μT

Methods

Results

Conclusion