John M. Pauly^1
1Electrical Engineering, Stanford University, Stanford, CA, United States

Many different methods have been explored over the years for using NMR for imaging and characterizing materials.   Some of these have carried forward into MRI, but there are many other interesting variations that can make MRI more portable and flexible.  This presentation will outline some of these ideas, and describe where they may have a place in the future of MRI systems.

Clarissa Zimmerman Cooley^1
1A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States

As the premiere modality for brain imaging, MRI could find wider applicability if lightweight, portable systems were available for siting in unconventional locations. We construct and validate a truly portable (<100kg) and silent proof-of-concept scanner which replaces conventional gradient encoding with a rotating inhomogeneous low-field magnet. When rotated about the object, the inhomogeneous field pattern is used to create generalized projections. The system is validated with experimental 2D images, and extended to 3D imaging with the addition of Transmit Array Spatial Encoding (TRASE). This new scanner architecture demonstrates the potential for portability by simultaneously relaxing the magnet homogeneity criteria and eliminating the gradient coil.

Fa-Hsuan Lin^1
1National Taiwan University

Recent progress has demonstrated the feasibility of using the SQUID sensor arrays in MEG helmets to record MRI data. Here we describe the basic principles of MRI as well as the special requirements and solutions needed to perform ultra-low-field MRI concurrently with MEG. We consider it is feasible to build practical MEG-MRI instruments for scientific experimentation and for clinical use. An MRI with 2 mm spatial resolution, sufficient signal-to-noise ratio and contrast appears achievable without essentially lengthening the normal MEG measurement time.

Matthew S Rosen^1,2,3
1MGH/Martinos Center, Charlestown, MA, United States, ²Department of Radiology, Harvard Medical School, Boston, MA, United States, ³Department of Physics, Harvard University, Cambridge, MA, United States

MRI is unparalleled in its ability to visualize anatomical structure and function non-invasively. To overcome the low sensitivity inherent in inductive detection of weakly polarized nuclear spins, the vast majority of clinical MRI scanners employ massive superconducting Tesla-scale magnets with strict infrastructure demands that preclude truly portable operation. We describe here a simple, non-cryogenic approach to high-performance human MRI at ultra-low magnetic field using undersampled b-SSFP at 6.5 mT. We contend that practical ultra-low magnetic-field implementations of MRI (< 10 mT) will complement traditional MRI, providing clinically relevant images and setting new standards for affordable and robust portable devices.