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Wed, July 10, 2013
We present in vivo images of the human brain acquired with an ultralow field magnetic resonance imaging (ULF-MRI) system operating at a field B0 130 microtesla. The system features pre-polarization of the proton spins at a field Bp 0.1 T and detection of the nuclear magnetic resonance signals with a SQUID-based, superconducting, second-derivative gradiometer. We report measurements of the longitudinal relaxation time T1 of brain tissue, cerebrospinal fluid (CSF), blood and scalp fat at both B0 and Bp. These measurements enable us to construct inversion recovery sequences that we combine with a Carr-Purcell-Meiboom-Gill (CPMG) echo train to obtain images in which any given tissue can be nulled out and another tissue highlighted. Such techniques greatly enhance the already high intrinsic T1-contrast obtainable at ULF. We illustrate the power of this technique with an image showing only the superior sagittal sinus, with other components eliminated. We further show that, as expected at ULF, the transverse relaxation time T2 approaches T1 in all four brain components. We present T2-weighted images that with our technique can be acquired in about 20% of the time required for T1-weighted images and comparable tissue contrast. With the use of multiple sensors, for example, those in a SQUID-based system for magnetic source imaging, we believe these techniques would enable one to obtain high-contrast imaging of the components of the brain, including the visualization of brain tumors without the need of a contrast agent.
Magnetic Resonance Imaging of the Human Head at 130 Microtesla