Read by QxMD icon Read

Journal of Magnetic Resonance

W Th Wenckebach
The fundamental process of dynamic nuclear polarization (DNP) via the cross effect (CE) and thermal mixing (TM) is a triple spin flip, in which two interacting electron spins and a nuclear spin interacting with one of these electron spins flip together. In the previous article (Wenckebach, 2018) these triple spin flips were treated by first determining the eigenstates of the two interacting electron spins exactly and next investigating transitions involving these exact eigenstates and the nuclear spin states...
December 23, 2018: Journal of Magnetic Resonance
W Th Wenckebach
In dynamic nuclear polarization (DNP) via the cross effect (CE) and thermal mixing (TM) a microwave field first reduces the polarization of some electron spins, so the electron spin system deviates from thermal equilibrium with the lattice. Next, the mutual interactions combine with their interaction with the nuclear spins to transform this deviation into nuclear spin polarization. Two approaches were introduced to describe the latter process. The fluctuating field approach considers the electron spins to fluctuate between their up and down states due to their mutual interactions...
December 22, 2018: Journal of Magnetic Resonance
Michael Mullen, Naoharu Kobayashi, Michael Garwood
Applications of multidimensional spatially-selective pulses are sometimes limited by their long pulse durations resulting from the need to execute a modulated gradient waveform in concert with RF transmission. Here, we introduce a method to design two-dimensional selective adiabatic pulses using a Cartesian k-space trajectory. The full pulse can be sampled using various undersampled segments to create a multidimensional pulse resilient to large off-resonances. Moreover, the pulse can be designed to be resilient to B1 + inhomogeneity...
December 19, 2018: Journal of Magnetic Resonance
Raynald Giovine, Julien Trébosc, Frédérique Pourpoint, Olivier Lafon, Jean-Paul Amoureux
In solid-state NMR spectroscopy, the through-space transfer of magnetization from protons to quadrupolar nuclei is employed to probe proximities between those isotopes. Furthermore, such transfer, in conjunction with Dynamic Nuclear Polarization (DNP), can enhance the NMR sensitivity of quadrupolar nuclei, as it allows the transfer of DNP-enhanced 1 H polarization to surrounding nuclei. We compare here the performances of two approaches to achieve such transfer: PRESTO (Phase-shifted Recoupling Effects a Smooth Transfer of Order), which is currently the method of choice to achieve the magnetization transfer from protons to quadrupolar nuclei and which has been shown to supersede Cross-Polarization under Magic-Angle Spinning (MAS) for quadrupolar nuclei and D-RINEPT (Dipolar-mediated Refocused Insensitive Nuclei Enhanced by Polarization Transfer) using symmetry-based SR41 2 recoupling, which has already been employed to transfer the magnetization in the reverse way from half-integer quadrupolar spin to protons...
December 18, 2018: Journal of Magnetic Resonance
Hongwei Sun, Stephanie Yong, Jonathan C Sharp
TRASE is an MRI k-space encoding method that uses radio-frequency (RF or B1 ) transmit phase gradient fields to achieve millimeter-level spatial resolution. Image quality is critically dependent upon the efficient generation of B1 fields with uniform magnitude and strong phase gradients. We present the design of a new family of phase gradient transmit coil based upon a solenoid twisted about a transverse axis. This design has many attractive geometric, electrical and magnetic characteristics, including the capability to spatially encode in the direction of the main static B0 field without obstructing access to the bore...
December 17, 2018: Journal of Magnetic Resonance
David Ariando, Cheng Chen, Mason Greer, Soumyajit Mandal
This paper describes the development of a portable and self-optimizing NMR spectrometer based on a miniaturized custom analog front-end and a System-on-Chip (SoC)-based digital back-end. The SoC integrates a field-programmable gate array (FPGA) fabric with a hard processor running a Linux operating system, thus enabling fully-autonomous operation without the need for an external computer. In the proposed approach, data captured by the FPGA fabric during regular operation is transported to the hard processor using an integrated on-chip bus for further processing...
December 15, 2018: Journal of Magnetic Resonance
Gregory Furman, Victor Meerovich, Vladimir Sokolovsky, Yang Xia
Study of the spin-lattice relaxation in the spin-locking state offers important information about atomic and molecular motions, which cannot be obtained by spin lattice relaxation in strong external magnetic fields. The application of this technique for the investigation of the spin-lattice relaxation in biological samples with fibril structures reveals an anisotropy effect for the relaxation time under spin locking, T1ρ . To explain the anisotropy of the spin-lattice relaxation under spin-locking in connective tissue a model which represents a tissue by a set of nanocavities containing water is used...
December 15, 2018: Journal of Magnetic Resonance
Irena Zivkovic, Wouter Teeuwisse, Alexey Slobozhanyuk, Elizaveta Nenasheva, Andrew Webb
OBJECTIVE: The purpose of this work is to investigate the use of ceramic materials (based on BaTiO3 with ZrO2 and CeO2 -additives) with very high relative permittivity (εr  ∼ 4500) to increase the local transmit field and signal-to-noise ratio (SNR) for commercial extremity coils on a clinical 1.5 T MRI system. METHODS: Electromagnetic simulations of transmit efficiency and specific absorption rate (SAR) were performed using four ferroelectric ceramic blocks placed around a cylindrical phantom, as well as placing these ceramics around the wrist of a human body model...
December 15, 2018: Journal of Magnetic Resonance
Camilla Terenzi, Andrew J Sederman, Michael D Mantle, Lynn F Gladden
In the last decades, the 1 H NMR T2 -T2 relaxation-exchange (REXSY) technique has become an essential tool for the molecular investigation of simple and complex fluids in heterogeneous porous solids and soft matter, where the mixing-time-evolution of cross-correlated T2 -T2 peaks enables a quantitative study of diffusive exchange kinetics in multi-component systems. Here, we present a spatially-resolved implementation of the T2 -T2 correlation technique, named z-T2 -T2 , based on one-dimensional spatial mapping along z using a rapid frequency-encode imaging scheme...
December 14, 2018: Journal of Magnetic Resonance
Kulam Najmudeen Magdoom, Ahmad Zeinomar, Russell R Lonser, Malisa Sarntinoranont, Thomas H Mareci
Creeping flows govern many important physiological phenomena such as elevated interstitial fluid flows in tumors, glymphatic flows in the brain, among other applications. However, few methods exist to measure such slow flows non-invasively in optically opaque biological tissues in vivo. Phase-contrast MRI is a velocimetry technique routinely used in the clinic to measure fast flows in biological tissues, such as blood and cerebrospinal fluid (CSF), in the order of cm/s. Use of this technique to encode slower flows is hampered by diffusion weighting and phase error introduced by gradient hardware imperfections...
December 14, 2018: Journal of Magnetic Resonance
Randall Pursley, Ayano Enomoto, Haitao Wu, Jeffrey R Brender, Thomas Pohida, Sankaran Subramanian, Murali C Krishna, Nallathamby Devasahayam
An excessive RF power requirement is one of the main obstacles in the clinical translation of EPR imaging. The radio frequency (RF) pulses used in EPR imaging to excite electron spins must be very short to match their fast relaxation. With traditional pulse schemes and ninety degree flip angles, this can lead to either unsafe specific absorption rate (SAR) levels or unfeasibly long repetition times. In spectroscopy experiments, it has been shown that stochastic excitation and correlation detection can reduce the power while maintaining sensitivity but have yet to be applied to imaging experiments...
December 14, 2018: Journal of Magnetic Resonance
S Bussandri, L Buljubasich, R H Acosta
Despite the large degree of polarization in PHIP experiments compared to the Boltzmann factor, the presence of a large amount of non-reacted molecules with thermal polarization is an important obstacle when dealing with very diluted samples. The feasibility of enhancing both sensitivity and resolution in a single experiment by combining two well established pulse sequences, OPSY and PHD-PHIP is presented. OPSY is used as a block for filtering the signals originated from thermally polarized protons. PhD-PHIP, on the other hand, is used as an acquisition block, increasing the resolution and further improving the sensitivity by preventing signal canceling in the presence of magnetic field inhomogeneities...
December 7, 2018: Journal of Magnetic Resonance
Dan Xiao, Bruce J Balcom
T2 relaxation time measurement is a powerful tool to distinguish signal components in porous media. As T2 weighting is generally achieved by spin-echo based methods, it is very challenging to capture very short T2 relaxation time components, approximately 1 ms, with high resolution spatial encoding. It is especially challenging when T2 relaxation times of the other signal components are not known a priori. We propose a method, combining ultrashort echo time (UTE) imaging with multiple spin echo refocusing, to generate a series of images with T2 weighting...
December 6, 2018: Journal of Magnetic Resonance
Kevin Singewald, Matthew J Lawless, Sunil Saxena
There is increasing evidence that the stability, structure, dynamics, and function of many proteins differ in cells versus in vitro. The determination of protein structure and dynamics within the native cellular environment may lead to better understanding of protein behavior. Electron spin resonance (ESR) has emerged as a technique that can report on protein structure and dynamics within cells. Nitroxide based spin labels are capable of reporting on protein dynamics, structure, and backbone flexibility but are limited due to nitroxide reduction occurring in cells...
December 6, 2018: Journal of Magnetic Resonance
Sergey Milikisiyants, Maxim A Voinov, Antonin Marek, Morteza Jafarabadi, Jing Liu, Rong Han, Shenlin Wang, Alex I Smirnov
Over the past decades pulsed electron-electron double resonance (PELDOR), often called double electron-electron resonance (DEER), became one of the major spectroscopic tools for measurements of nanometer-scale distances and distance distributions in non-crystalline biological and chemical systems. The method is based on detecting the amplitude of the primary (3-pulse DEER) or refocused (4-pulse DEER) spin echo for the so-called "observer" spins when the other spins coupled to the former by a dipolar interaction are flipped by a "pump" pulse at another EPR frequency...
December 5, 2018: Journal of Magnetic Resonance
Vratislav Blechta, Jan Sýkora
The approach to the measurement of one-bond indirect spin-spin coupling constants between equivalent nuclei was revisited. The analytical formulas for development of the density matrix of strongly coupled symmetrical HC-C'H' spin systems were derived and the optimal duration of polarization delay in the original 2QHMBC pulse sequence is discussed. Based on the analytical formulas a new version of a robust indirect detection experiment, called SYMONA (SYmmetrical MOlecules Natural Abundance double-quantum experiment), was proposed for carbon-carbon coupling constants detection in symmetrical molecules...
December 5, 2018: Journal of Magnetic Resonance
L R Buschle, F T Kurz, T Kampf, H P Schlemmer, C H Ziener
We analyze the gradient echo signal in the presence of blood vessel networks. Both, diffusion and susceptibility effects are analytically emphasized within the Bloch-Torrey equation. Solving this equation, we present the first exact description of the local magnetization around a single vessel. This allows us to deduce the gradient echo signal of parallel vessels randomly distributed in a plane, which is valid for arbitrary mean vessel diameters in the range of physiological relevant blood volume fractions...
November 30, 2018: Journal of Magnetic Resonance
Pavlo Bielytskyi, Daniel Gräsing, Stefan Zahn, Kaustubh R Mote, A Alia, P K Madhu, Jörg Matysik
Modified versions of through-bond heteronuclear correlation (HETCOR) experiments are presented to take advantage of the light-induced hyperpolarization that occurs on 13 C nuclei due to the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect. Such 13 C-1 H photo-CIDNP MAS-J-HMQC and photo-CIDNP MAS-J-HSQC experiments are applied to acquire the 2D 13 C-1 H correlation spectra of selectively 13 C-labeled photochemically active cofactors in the frozen quinone-blocked photosynthetic reaction center (RC) of the purple bacterium Rhodobacter (R...
November 29, 2018: Journal of Magnetic Resonance
C H Ziener, T Kampf, F T Kurz, H P Schlemmer, L R Buschle
Magnetic resonance imaging of lung tissue is strongly influenced by susceptibility effects between spin-bearing water molecules and air-filled alveoli. The measured lineshape, however, also depends on the interplay between susceptibility effects and blood-flow around alveoli that can be approximated as pseudo-diffusion. Both effects are quantitatively described by the Bloch-Torrey-equation, which was so far only solved for dephasing on the alveolar surface. In this work, we extend this model to the whole range of physiological relevant air volume fractions...
November 29, 2018: Journal of Magnetic Resonance
Michael C D Tayler, Lynn F Gladden
Nuclear magnetic resonance signals for 1 H in simple chlorinated, brominated and deuterated liquids were detected at field strengths between 1 nT and a few μT to investigate the influence of scalar relaxation of the second kind (SR2K). SR2K describes the acceleration in magnetization decay rate for a spin-1/2 nucleus that is scalar coupled to a fast-relaxing quadrupolar nucleus. In agreement with simple theoretical models, the experimental data show that couplings to nuclei with small, nonzero quadrupole moments (2 H) give rise to higher transverse relaxation rates at ultralow field than rapidly relaxing quadrupolar nuclei (Cl and Br)...
November 28, 2018: Journal of Magnetic Resonance
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"