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STP456 - Multi-channel SQUID-based Ultra-Low Field Magnetic Resonance Imaging in Unshielded Environment

Multi-channel SQUID-based Ultra-Low Field Magnetic Resonance Imaging in Unshielded Environment
 
Andrei Matlashov, Per Magnelind, Shaun Newman, Henrik Sandin, Algis Urbaitis, Petr Volegov, Michelle Espy
 
Department of Physics, Applied Modern Physics Group
Los Alamos National Laboratory
Los Alamos, USA
 
 
Abstract — Magnetic Resonance Imaging (MRI) is the best method for non-invasive imaging of soft tissue anatomy. A conventional MRI relies on 1.5–3 T fixed strength magnetic fields, with parts-per-million homogeneity, requiring large and expensive magnets. MRI can be done at ultra-low magnetic fields (ULF) with Larmor frequencies of a few kHz with much more modest magnetic system requirements. However the ULF regime requires a very sensitive detection system. A candidate detection system is based on SQUID gradiometers. A conventional SQUID gradiometer based detection system requires effective shielding from all ambient electromagnetic noise. Large shielded structures, such as magnetically shielded or eddy-current rooms, can be used for proof-of-principles experiments but do not lead to practical deployable instruments. Our goal is to develop a technique in which a SQUID-based detector array could be deployed without the limitation imposed by the requirement for a shielded structure. We have tested a 7-channel ULF MRI system located in unshielded environment inside a modern physics laboratory. It was possible to significantly suppress most of the electromagnetic interference by subtracting the signal from a one-channel reference magnetometer located nearby. We believe that the influence of the pre-polarization coil produces kHz-range frequency noise in gradiometer channels that is very well correlated with the signal from the magnetometer.

Keywords (Index Terms) — ULF MRI, SQUID, shielding, noise compensation.

IEEE/CSC & ESAS SUPERCONDUCTIVITY NEWS FORUM (global edition), July 2015.
Selected August 6, 2015. Reference STP456; Category 4. 
Contributed presentation SQ-O08 given at ISEC 2015; Nagoya, Japan, July 6 – 9, 2015. 
Final version of the corresponding paper will be published by IEEE XPLORE.