Ultra-low field magnetic resonance imaging detection with gradient tensor compensation in urban unshielded environment

Abstract

An ultra-low field (ULF) magnetic resonance imaging (MRI) system was set up in an urban laboratory without magnetic shielding. The measured environmental gradient fields of 1 ∼ 5 μT/m caused image distortion. We designed a gradient detection and compensation system to effectively balance the gradient tensor components. The free induction decay signal duration of tap water was thus extended from 0.3 s to 2.5 s, providing the possibility for high-resolution imaging. Two-dimensional MRI images were then obtained at 130 μT with a helium-cooled second-order superconducting quantum interference device gradiometer. This result allows us to develop an inexpensive ULF MRI system for biological studies.