On the feasibility of neurocurrent imaging by low-field nuclear magnetic resonance

Burghoff, M.; Albrecht, Hans-Helge; Hartwig, Stefan; Hilschenz, Ingo; Körber, Rainer; Höfner, Nora; Scheer, Hans-Jürgen; Voigt, Jens; Trahms, Lutz; Curio, Gabriel

doi:10.1063/1.3441410

Cited by 26 publications

(6 citation statements)

References 15 publications

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“…The T 1 relaxation rate increases roughly proportionally to the agarose content, so that the dispersion curves of the two samples differ by a factor of two but exhibit similar shapes. To the measured dependence of 1/T 1 over B, we fitted Cole-Cole expression curves, (8), which are also shown in Fig. 2; the obtained parameters and their standard errors are listed in Table 1.…”

Section: Resultsmentioning

confidence: 99%

“…Apparently, T 1 relaxation times of these tissue samples exhibit a dispersion that changes significantly towards lower Larmor frequencies, a behavior that facilitates the observation of contrast by ULF MRI. Other proposed applications of ULF MRI include detection of liquid explosives [4], hybrid magnetoencephalography-MRI [5,6], and direct imaging of neuronal currents [7,8]. The polarization method introduced in this paper is a technique that future optimized ULF-MRI scanners may benefit from.…”

Section: Introductionmentioning

confidence: 99%

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Improved Contrast in Ultra-Low-Field MRI with Time-Dependent Bipolar Prepolarizing Fields: Theory and NMR Demonstrations

Nieminen¹,

Voigt²,

Hartwig³

et al. 2013

Metrology and Measurement Systems

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The spin lattice (T 1 ) relaxation rates of materials depend on the strength of the external magnetic field in which the relaxation occurs. This T 1 dispersion has been suggested to offer a means to discriminate between healthy and cancerous tissue by performing magnetic resonance imaging (MRI) at low magnetic fields. In prepolarized ultra-low-field (ULF) MRI, spin precession is detected in fields of the order of 10-100 μT. To increase the signal strength, the sample is first magnetized with a relatively strong polarizing field. Typically, the polarizing field is kept constant during the polarization period. However, in ULF MRI, the polarizing field strength can be easily varied to produce a desired time course. This paper describes how a novel variation of the polarizing field strength and duration can optimize the contrast between two types of tissue having different T 1 relaxation dispersions. In addition, NMR experiments showing that the principle works in practice are presented. The described procedure may become a key component for a promising new approach of MRI at ultra-low fields.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improved Contrast in Ultra-Low-Field MRI with Time-Dependent Bipolar Prepolarizing Fields: Theory and NMR Demonstrations

Nieminen¹,

Voigt²,

Hartwig³

et al. 2013

Metrology and Measurement Systems

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“…Direct neural imaging (DNI), also termed as neuronal current imaging, aims to detect neuronal activity directly in high [2][3][4] or ultralow magnetic field. [5][6][7] The basic idea in these is to measure changes in the magnetic resonance signal due to altered spin dynamics caused by the magnetic field arising from the neuronal activity. In smaller scale, technology for invasive measurement of neuromagnetic fields inside the head, even directly in the cortex, is being developed.…”

Section: Introductionmentioning

confidence: 99%

The magnetic field inside a layered anisotropic spherical conductor due to internal sources

Nieminen

Stenroos

2016

Journal of Applied Physics

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Recent advances in neuronal current imaging using magnetic resonance imaging and in invasive measurement of neuronal magnetic fields have given a need for methods to compute the magnetic field inside a volume conductor due to source currents that are within the conductor. In this work, we derive, verify, and demonstrate an analytical expression for the magnetic field inside an anisotropic multilayer spherically symmetric conductor due to an internal current dipole. We casted an existing solution for electric field to vector spherical harmonic (VSH) form. Next, we wrote an ansatz for the magnetic field using toroidal-poloidal decomposition that uses the same VSHs. Using properties of toroidal and poloidal components and VSHs and applying magnetic scalar potential, we then formulated a series expression for the magnetic field. The convergence of the solution was accelerated by formulating the solution using an addition-subtraction method. We verified the resulting formula against boundary-element method. The verification showed that the formulas and implementation are correct; 99th percentiles of amplitude and angle differences between the solutions were below 0.5% and 0.5 , respectively. As expected, the addition-subtraction model converged faster than the unaccelerated model; close to the source, 250 terms gave relative error below 1%, and the number of needed terms drops fast, as the distance to the source increases. Depending on model conductivities and source position, field patterns inside a layered sphere may differ considerably from those in a homogeneous sphere. In addition to being a practical modeling tool, the derived solution can be used to verify numerical methods, especially finite-element method, inside layered anisotropic conductors. V

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“…[12][13][14] are prominent examples of advanced measurement systems where a strong pulsed B p , low-noise SQUID sensors, and a magnetically shielded room (MSR) with a high shielding factor are all required in a single integrated system. In the simultaneous MEG-lT-MRI operation, the strong B p is required for lT-NMR operation and the low-noise SQUID sensors and MSR are necessary to pick up weak MEG signals.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of cancellation coil for precision magnetic measurements with strong prepolarization field inside shielded environment

Hwang

Kim

Kang

et al. 2012

Journal of Applied Physics

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On the feasibility of neurocurrent imaging by low-field nuclear magnetic resonance

Cited by 26 publications

References 15 publications

Improved Contrast in Ultra-Low-Field MRI with Time-Dependent Bipolar Prepolarizing Fields: Theory and NMR Demonstrations

Improved Contrast in Ultra-Low-Field MRI with Time-Dependent Bipolar Prepolarizing Fields: Theory and NMR Demonstrations

The magnetic field inside a layered anisotropic spherical conductor due to internal sources

Evaluation of cancellation coil for precision magnetic measurements with strong prepolarization field inside shielded environment

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