Parallel MRI at microtesla fields

Zotev, Vadim; Volegov, P. L.; Matlashov, Andrei; Espy, Michelle A.; Mosher, John C.; Kraus, R.H.

doi:10.1016/j.jmr.2008.02.015

Cited by 67 publications

(58 citation statements)

References 44 publications

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“…Finally, other techniques developed for HFMRI are applicable to ULFMRI. Parallel imaging with multiple sensors has already been demonstrated at ULF (27,35). Imaging times may also be shortened by filling k-space asymmetrically using partial Fourier encoding (4,53) in the phase encoding dimension.…”

Section: Discussion and Outlookmentioning

confidence: 99%

MRI of the human brain at 130 microtesla

Inglis

Buckenmaier

SanGiorgio

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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We present in vivo images of the human brain acquired with an ultralow field MRI (ULFMRI) system operating at a magnetic field B 0 ∼ 130 μT. The system features prepolarization of the proton spins at B p ∼ 80 mT and detection of the NMR signals with a superconducting, second-derivative gradiometer inductively coupled to a superconducting quantum interference device (SQUID). We report measurements of the longitudinal relaxation time T 1 of brain tissue, blood, and scalp fat at B 0 and B p , and cerebrospinal fluid at B 0 . We use these T 1 values to construct inversion recovery sequences that we combine with Carr-Purcell-Meiboom-Gill echo trains to obtain images in which one species can be nulled and another species emphasized. In particular, we show an image in which only blood is visible. Such techniques greatly enhance the already high intrinsic T 1 contrast obtainable at ULF. We further present 2D images of T 1 and the transverse relaxation time T 2 of the brain and show that, as expected at ULF, they exhibit similar contrast. Applications of brain ULFMRI include integration with systems for magnetoencephalography. More generally, these techniques may be applicable, for example, to the imaging of tumors without the need for a contrast agent and to modalities recently demonstrated with T 1ρ contrast imaging (T 1 in the rotating frame) at fields of 1.5 T and above. . 3D magnetic field gradients specify a unique magnetic field and thus an NMR frequency or phase in each voxel of the subject, so that with appropriate signal decoding one can acquire a 3D image (4).Clinical MRI systems with B 0 = 1:5 T achieve a spatial resolution of typically 1 mm; 3-T systems are becoming increasingly widespread in clinical practice (5), offering a higher signal-tonoise ratio (SNR) and thus higher spatial resolution. Nonetheless, there is ongoing interest in less expensive MRI systems operating at lower fields. Commercially available 0.2-to 0.5-T systems based on permanent magnets offer both lower cost and wider patient aperture than their higher field counterparts, at the expense of spatial resolution. At the still lower field of 0.03 T maintained by a room temperature solenoid, Connolly and coworkers (6, 7) obtained clinically useful SNR and spatial resolution by prepolarizing the protons in a field B p of 0.3 T. Prepolarization (8) enhances the magnetization of the proton ensemble over that produced by the lower precession field; after the polarizing field is removed, the higher magnetization produces a correspondingly larger signal during its precession in B 0 . Using the same method, Stepisnik et al. (9) obtained MR images in the Earth's magnetic field (∼ 50 μT).In recent years there has been increasing interest (10-36) in NMR and MRI at fields ranging from a few nanotesla to the order of 100 μT. The enormous reduction in the detected signal amplitude compared with the high field value is overcome partly by using prepolarization and partly by detecting the signal with an untuned superconducting input circuit inductively coupl...

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Section: Discussion and Outlookmentioning

confidence: 99%

MRI of the human brain at 130 microtesla

Inglis

Buckenmaier

SanGiorgio

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…Obvious examples of such situations can be found in very-low-and ultra-low-field NMR and MRI (11), where recent innovation has largely been driven through in-house development of novel MR systems operating in the microtesla and millitesla ranges (12)(13)(14)(15)(16)(17)(18). In this limit, NMR-based measurements of field gradients (8,9) can be complicated by the need for physically large proton-based phantoms (required for sufficient signal) or the unnecessary consumption of the costly hyperpolarized media that are used in many low-field MR applications (13)(14)(15)(16).…”

Section: Introductionmentioning

confidence: 99%

A simple wide‐band gradiometer for operation in very low background field

Bidinosti

Zhang

Hayden

2010

Concepts Magn Reson

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A simple gradiometer, capable of sensing submicrotesla changes in magnetic field with 10-ls resolution, is constructed from a pair of low-cost, wide-band Halleffect sensors output to a voltage preamplifier and digital storage oscilloscope. The linear operational range of the sensors (67.5 mT) limits typical applications, such as gradient coil development and testing, to environments where background fields are very low. The gradiometer is ideal for characterizing gradient field rise times and waveforms in this limit and applications pertinent to very-low-field nuclear magnetic resonance and magnetic resonance imaging are presented.

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“…As the measurement magnetic fields are very low (lT), the technique is applied in the ultra-low field (ULF) regime. Previous work indicates that SQUIDbased ULF NMR is a very rich technique with applications to many problems [3][4][5][6][7] from medical imaging to fundamental physics. However, in the nEDM experiment, the signal is very small because the fractional density of the nearly 100%-polarized 3 He atoms in the superfluid 4 He will be only 10 À10 (2 Â 10 12 atoms/cm 3 ) [2].…”

Section: Introductionmentioning

confidence: 99%