An active feedback scheme for low field NMR experiments

Baudin, Emmanuel; Safiullin, K. R.; Morgan, Steven W.; Nacher, Pierre-Jean

doi:10.1088/1742-6596/294/1/012009

Cited by 12 publications

(16 citation statements)

References 12 publications

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“…However, significantly increasing in vivo ATs would require the use of radicals with longer‐term in vivo stability . NMR sensitivity would be further improved by reducing coil noise, by implementing either a cryocooled coil or active feedback …”

Section: Discussionmentioning

confidence: 99%

“…46 NMR sensitivity would be further improved by reducing coil noise, by implementing either a cryocooled coil 47 or active feedback. 48 Our custom OMRI probe has been designed for a high Q-factor in the NMR resonator and low SAR from the EPR resonator. While the homogeneity of our volume EPR resonator is highly favorable for imaging, as inductive heating scales as the fifth power of sample radius, 49 the use of surface EPR coils for B 1e confinement will be necessary for samples much larger than a rat's head.…”

Section: Discussionmentioning

confidence: 99%

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An Overhauser‐enhanced‐MRI platform for dynamic free radical imaging in vivo

et al. 2018

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Overhauser-enhanced MRI (OMRI) is an electron-proton double-resonance imaging technique of interest for its ability to non-invasively measure the concentration and distribution of free radicals. In vivo OMRI experiments are typically undertaken at ultra-low magnetic field (ULF), as both RF power absorption and penetration issues-a consequence of the high resonance frequencies of electron spins-are mitigated. However, working at ULF causes a drastic reduction in MRI sensitivity. Here, we report on the design, construction and performance of an OMRI platform optimized for high NMR sensitivity and low RF power absorbance, exploring challenges unique to probe design in the ULF regime. We use this platform to demonstrate dynamic imaging of TEMPOL in a rat model. The work presented here demonstrates improved speed and sensitivity of in vivo OMRI, extending the scope of OMRI to the study of dynamic processes such as metabolism.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

An Overhauser‐enhanced‐MRI platform for dynamic free radical imaging in vivo

et al. 2018

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“…A pair of rectangular detection coils (7.5×10.5 cm 2 , 4 cm apart, with 72 turns each of 25×0.1-mm Litz wire) were tuned as a tank circuit using a C0G capacitor, yielding a quality factor Q=180. An active feedback scheme was used to avoid long ring-down dead times following rf pulses and to obtain a broad enough detection bandwidth, suitable for MRI, without SNR penalty [39]. An Apollo Tecmag console was used to manage non-selective rf excitation, preamplifier blanking, and gradient pulses for 2-D imaging.…”

Section: Experimental System and Methodsmentioning

confidence: 99%

Achieving high spatial resolution and high SNR in low-field MRI of hyperpolarised gases with Slow Low Angle SHot

Safiullin¹,

Talbot²,

Nacher³

2013

Journal of Magnetic Resonance

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MRI of hyperpolarised gases is usually performed with fast data acquisition to achieve high spatial resolutions despite rapid diffusion-induced signal attenuation. We describe a double-cross k-space sampling scheme suitable for slow low angle shot (SLASH) acquisition and yielding an increased SNR. It consists of a series of anisotropic partial acquisitions with a reduced resolution in the read direction, which alleviates signal attenuation and still provides a high isotropic resolution. The advantages of SLASH imaging over conventional FLASH imaging are evaluated analytically, using numerical lattice calculations, and experimentally in phantom cells filled with hyperpolarised 3 He-N2 gas mixtures. Low-field MRI is performed (here 2.7 mT), a necessary condition to obtain long T * 2 values in lungs for slow acquisition. Two additional benefits of the SLASH scheme over FLASH imaging have been demonstrated: it is less sensitive to the artefacts due to concomitant gradients and it allows measuring apparent diffusion coefficients for an extended range of times.

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“…The benefits to SNR can be clearly observed in Fig. 7, by comparing columns (2) and (5) where there is no damping in the window, to columns (3) and (7) where damping, DF = 10, is left on during the window. Combining both phase-cycling and damping during acquisition, permits us to retain the sensitivity of the magnetometer even in the presence of ringing, Fig.…”

Section: Fit Parametersmentioning

confidence: 98%

Spin damping in an rf atomic magnetometer

2013

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Under negative feedback, the quality factor Q of a radio-frequency magnetometer can be decreased by more than two orders of magnitude, so that any initial perturbation of the polarized spin system can be rapidly damped, preparing the magnetometer for detection of the desired signal. We find that noise is also suppressed under such spin-damping, with a characteristic spectral response corresponding to the type of noise; therefore magnetic, photon-shot, and spin-projection noise can be measured distinctly. While the suppression of resonant photon-shot noise implies the closed-loop production of polarization-squeezed light, the suppression of resonant spin-projection noise does not imply spin-squeezing, rather simply the broadening of the noise spectrum with Q.Furthermore, the application of spin-damping during phase-sensitive detection suppresses both signal and noise in such a way as to increase the sensitivity bandwidth. We demonstrate a three-fold increase in the magnetometer's bandwidth while maintaining 0.3 fT/ √ Hz

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An active feedback scheme for low field NMR experiments

Cited by 12 publications

References 12 publications

An Overhauser‐enhanced‐MRI platform for dynamic free radical imaging in vivo

An Overhauser‐enhanced‐MRI platform for dynamic free radical imaging in vivo

Achieving high spatial resolution and high SNR in low-field MRI of hyperpolarised gases with Slow Low Angle SHot

Spin damping in an rf atomic magnetometer

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