Project

Nuclear Spin Noise

Goal: Exploring fundamental properties and applications of transverse nuclear spin noise in spectroscopy and imaging

Date: 1 July 2005

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Norbert Müller
added a research item
Nuclear spin noise spectroscopy in the absence of radio frequency pulses was studied under the influence of pulsed field gradients (PFGs) on pure and mixed liquids. Under conditions where the radiation-damping-induced line broadening is smaller than the gradient-dependent inhomogeneous broadening, echo responses can be observed in difference spectra between experiments employing pulsed field gradient pairs of the same and opposite signs. These observed spin noise gradient echoes (SNGEs) were analyzed through a simple model to describe the effects of transient phenomena. Experiments performed on high-resolution nuclear magnetic resonance (NMR) probes demonstrate how refocused spin noise behaves and how it can be exploited to determine sample properties. In bulk liquids and their mixtures, transverse relaxation times and translational diffusion constants can be determined from SNGE spectra recorded following tailored sequences of magnetic field gradient pulses.
Norbert Müller
added a research item
Nuclear spin noise spectroscopy in the absence of radio frequency pulses was studied under the influence of pulsed field gradients (PFGs) on pure and mixed liquids. Under conditions where the radiation-damping-induced line broadening is smaller than the gradient-dependent inhomogeneous broadening, echo responses can be observed in difference spectra between experiments employing pulsed field gradient pairs of the same and opposite signs. These observed spin noise gradient echoes (SNGEs) were analyzed through a simple model to describe the effects of transient phenomena. Experiments performed on high-resolution nuclear magnetic resonance (NMR) probes demonstrate how refocused spin noise behaves and how it can be exploited to determine sample properties. In bulk liquids and their mixtures, transverse relaxation times and translational diffusion constants can be determined from SNGE spectra recorded following tailored sequences of magnetic field gradient pulses.
Norbert Müller
added a research item
Nuclear spin-noise spectroscopy in absence of radio frequency pulses was studied under the influence of pulsed field gradients (PFGs) on pure and mixed liquids. Under conditions, where the radiation-damping induced line broadening is smaller than the gradient dependent inhomogeneous broadening, echo responses can be observed in difference spectra between experiments employing pulsed field gradient pairs of same and opposite signs. These observed “spin-noise gradient echoes” (SNGEs) were analyzed through a simple model to describe the effects of transient phenomena. Experiments performed on high resolution NMR probes demonstrate how “refocused spin noise” behaves and how it can be exploited to determine sample properties. In bulk liquids and their mixtures transverse relaxation times as well as translational diffusion constants can be determined from SNGE spectra recorded following tailored sequences of magnetic field gradient pulses.
Norbert Müller
added a research item
We report three-dimensional spin noise imaging (SNI) of nuclear spin density from spin noise data acquired by Faraday detection. Our approach substantially extends and improves the two-dimensional SNI method for excitation-less magnetic resonance tomography reported earlier (Müller and Jerschow, 2006). This proof of principle was achieved by taking advantage of the particular continuous nature of spin noise acquired in the presence of constant magnitude magnetic field gradients and recent advances in nuclear spin noise spectroscopy acquisition as well as novel processing techniques. In this type of projection–reconstruction-based spin noise imaging the trade-off between signal-to-noise ratio (or image contrast) and resolution can be adjusted a posteriori during processing of the original time-domain data by iterative image reconstruction in a unique way not possible in conventional rf-pulse-dependent magnetic resonance imaging (MRI). The 3D SNI is demonstrated as a proof of concept on a commercial 700 MHz high-resolution NMR spectrometer, using a 3D-printed polymeric phantom immersed in water.
Norbert Müller
added a research item
Norbert Müller
added a research item
A major breakthrough in speed and sensitivity of 2D spin-noise-detected NMR is achieved owing to a new acquisition and processing scheme called “double block usage” (DBU) that utilizes each recorded noise block in two independent cross-correlations. The mixing, evolution, and acquisition periods are repeated head-to-tail without any recovery delays and well- known building blocks of multidimensional NMR (constant- time evolution and quadrature detection in the indirect dimension as well as pulsed field gradients) provide further enhance- ment and artifact suppression. Modified timing of the receiver electronics eliminates spurious random excitation. We achieve a threefold sensitivity increase over the original snHMQC (spin-noise-detected heteronuclear multiple quantum correlation) experiment (K. Chandra et al., J. Phys. Chem. Lett. 2013, 4, 3853) and demonstrate the feasibility of spin-noise-detected long-range correlation.
Norbert Müller
added an update
In our recent review article a few references were incorrectly expanded from their abbreviations. We provide the corrected references here. Please note that the links provided in the original pdf-files available from the publisher are correct.
 
Norbert Müller
added a research item
Analytical applications of NMR exploit the widely assumed linearity of the NMR response with respect to the spin concentration. Deviations of this linearity are undesired and in this review some current approaches to tackle this problem are given. However, from a physics point of view, the nonlinearity is a more complex affair. Indeed, NMR as a primary representative of coherent spectroscopy can be viewed as an inherently nonlinear method, in particular with respect to the excitation amplitude. Even excluding this intrinsic property, amplitude response is not always found to be linear and several distinct fundamental nonlinearity or nonadditivity effects can be caused by spin interactions, which can either be internal to the specimen, or owed to feedback from the observation electronics as summarized here with references to the latest literature. Ways to avoid nonlinear response for quantitative NMR applications are summarized briefly.
Norbert Müller
added a research item
Nature Communications 8 : Article number: 13914 10.1038/ncomms13914 ( 2017 ); Published 9 January 2017 ; Updated 19 April 2017 This Article contains typographical errors in Equation 1, where the fraction line incorrectly extends across the entire equation.
Norbert Müller
added a project goal
Exploring fundamental properties and applications of transverse nuclear spin noise in spectroscopy and imaging
 
Hervé Desvaux
added a research item
Spin-noise appeal: Detection of NMR spin-noise is very appealing when dilute hyperpolarized species are considered. Continuous monitoring of the noise absorption at the Larmor frequency enables determination of T(1) and T(2)*, independently of the static magnetic field. An inductively coupled microcoil located inside the NMR tube (see picture) allows acquisition of (129)Xe spin-noise spectra without radio-frequency excitation.
Norbert Müller
added a research item
We report proton spin noise spectra of a hyperpolarized solid sample of commonly used “DNP (dynamic nuclear polarization) juice” containing TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxide) and irradiated by a microwave field at a temperature of 1.2 K in a magnetic field of 6.7 T. The line shapes of the spin noise power spectra are sensitive to the variation of the microwave irradiation frequency and change from dip to bump, when the electron Larmor frequency is crossed, which is shown to be in good accordance with theory by simulations. Small but significant deviations from these predictions are observed, which can be related to spin noise and radiation damping phenomena that have been reported in thermally polarized systems. The non-linear dependence of the spin noise integral on nuclear polarization provides a means to monitor hyperpolarization semi-quantitatively without any perturbation of the spin system by radio frequency irradiation.
Norbert Müller
added 18 research items
Previous studies have shown that tuning/matching conditions optimized for transmission and detection can be significantly different for a variety of commercial NMR probes. In addition, it was also shown that by optimizing reception tuning (as opposed to typical transmission or reflection tuning) one may in some cases obtain sensitivity enhancements by as much as 25-50%. In earlier work, spin-noise and absorbed circuit noise signals have also been used to characterize reception optima. In this work, we show how the length of the coaxial transmission line cable between the pre-amplifier and the probe affects the positions of the reception tuning optimum, the radiation damping strength, induced frequency shifts, as well as, the shape of the spin-noise and absorbed circuit noise line shapes.
We have assessed the potential of an alternative probe tuning strategy based on the spin-noise response for application in common high-resolution multi-dimensional biomolecular NMR experiments with water signal suppression on aqueous and salty samples. The method requires the adjustment of the optimal tuning condition, which may be offset by several 100 kHz from the conventional tuning settings using the noise response of the water protons as an indicator. Although the radio frequency-pulse durations are typically longer under such conditions, signal-to-noise gains of up to 22% were achieved. At salt concentrations up to 100 mM a substantial sensitivity gain was observed.
Hervé Desvaux
added 2 research items
The detection of minor species in the presence of large amounts of similar main components remains a key challenge in analytical chemistry, for instance, to obtain isotopic fingerprints. As an alternative to the classical NMR scheme based on coherent excitation and detection, here we introduce an approach based on spin-noise detection. Chemical shifts and transverse relaxation rates are determined using only the detection circuit. Thanks to a nonlinear effect in mixtures with small chemical shift dispersion, small signals on top of a larger one can be observed with increased sensitivity as bumps on a dip; the latter being the signature of the main magnetization. Experimental observations are underpinned by an analytical theory: the coupling between the magnetization and the coil provides an amplified detection capability of both small static magnetic field inhomogeneities and small NMR signals. This is illustrated by two-bond 12C/13C isotopic measurements.
The theoretical shapes of nuclear spin-noise spectra in NMR are derived by considering a receiver circuit with finite preamplifier input impedance and a transmission line between the preamplifier and the probe. Using this model, it becomes possible to reproduce all observed experimental features: variation of the NMR resonance linewidth as a function of the transmission line phase, nuclear spin-noise signals appearing as a “bump” or as a “dip” superimposed on the average electronic noise level even for a spin system and probe at the same temperature, pure in-phase Lorentzian spin-noise signals exhibiting non-vanishing frequency shifts. Extensive comparisons to experimental measurements validate the model predictions, and define the conditions for obtaining pure in-phase Lorentzian-shape nuclear spin noise with a vanishing frequency shift, in other words, the conditions for simultaneously obtaining the spin-noise and frequency-shift tuning optima.
Norbert Müller
added 3 research items
In 1946 Bloch predicted that statistically incomplete cancellation of nuclear magnetic moments can give rise to a weak randomly fluctuating rf-signal even in a spin system at equilibrium. Experimental verification of this so-called spin noise was achieved much later using different approaches. The theory of spin noise detection is based on modified Nyquist noise equations, which however does not describe the tuning behaviour of existing high performance NMR probes accurately. There is a distinct tuning dependence of the spin noise signal. The negative noise signal (actually a dip in the noise power baseline) should be detected, at the optimum of the tuning curve. The symmetric “dip” line shape is most often observed at offsets exceeding hundreds of kHz from the conventional tuning optimum. Systematic investigation of experimental aspects and the application potential of NMR noise detection has lead to a new tuning strategy based on the spin noise tuning optimum, SNTO, which allows for substantial gains in the achievable signal-to-noise ratio with existing probes both in bio-molecular solution experiments and in solid state NMR. Combining hyper-polarization with NMR noise detection yielded new fundamental insights on the complex interplay of circuit noise and spin noise in particular the conceptual separation of pure spin noise and absorbed circuit noise.
NMR images were obtained from the proton spin noise signals of a water-containing phantom, which was placed in the highly tuned, low-noise resonant circuit of a cryogenically cooled NMR probe in the presence of systematically varied magnetic field gradients. The spatially resolved proton spin density was obtained from the raw signal by a modified projection–reconstruction protocol. Although spin noise imaging is inherently less sensitive than conventional magnetic resonance imaging, it affords an entirely noninvasive visualization of the interior of opaque objects or subjects. Thus, tomography becomes possible even when neither x-ray nor radio frequency radiation can be applied for technical or safety reasons. • magnetic resonance imaging • radiation-free imaging • sensitivity
A comprehensive description of how to record nuclear spin noise spectra on state-of-the-art commercial NMR spectrometers is given here, followed by a discussion of the current understanding of the physical underpinnings in a simplified manner. Several recent experimental manifestations and applications of the spin noise phenomenon such as spin noise imaging, noise-based probe tuning, and examples from liquid- and solid-state NMR spectroscopy as well as nuclear spin-based magnetic resonance force microscopy are also summarized here.