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Nuclear Magnetic Resonance
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Topic review
Updated time: 12 Jan 2021
Submitted by: Guanshu Liu
Definition: Recently, Chemical Exchange Saturation Transfer (CEST) MRI is emerging as an attractive approach with the capability of directly using low concentration, exchangeable protons-containing agents for generating quantitative MRI contrast. The ability to utilize diamagnetic compounds has been extensively exploited to detect many clinical compounds, such as FDA approved drugs, X-ray/CT contrast agents, nutrients, supplements, and biopolymers. The ability to directly off-label use clinical compounds permits CEST MRI to be rapidly translated to clinical settings.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 27 Oct 2020
Submitted by: Poul Erik Hansen
Definition: Humic substances are a very important part of our soil. The topic is description of the structure of humic substances using NMR. The NMR part is divided into two parts, liquid and solid state NMR. The assignment of NMR spectra are discussed and the structural elements that can be deduced from the spectral information. Principal Component Analysis is used as a tool to categorize the information. Structural models are discussed.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 22 Apr 2021
Submitted by: Michael Vaeggemose
Definition: MR spectroscopy (MRS) and spectroscopic imaging (MRSI) obtain metabolic information noninvasively from nuclei spins. For in vivo applications, common MR-active nuclei are protons (1H), phosphorus (31P), carbon (13C), sodium (23Na), and xenon (129Xe). The most common are protons due to their high gyromagnetic ratio and natural abundance in the human body. Since most metabolic processes involve carbon, 13C spectroscopy is a valuable method to measure in vivo metabolism noninvasively [1,2,3]. 13C spectra are characterized by a large spectral range (162–185 ppm), narrow line widths, and low sensitivity due to the low gyromagnetic ratio (a quarter as compared to protons) and natural abundance of 1.1% in vivo. However, the sensitivity can be increased with the use of 13C-enriched agents and by hyperpolarization.Hyperpolarized (HP) 13C MRI is a method that magnetizes 13C probes to dramatically increase signal as compared to conventional MRI [3]. Metabolic and functional HP 13C MRI is a promising diagnostic tool for detecting disorders linked to altered metabolism such as cancer, diabetes, and heart diseases [4], increasing sensitivity sufficiently to map metabolic pathways in vivo without the use of ionizing radiation, as in positron emission tomography (PET) imaging. Metabolic imaging using HP 13C compounds has been translated successfully into single-organ examinations in healthy controls and various patient populations.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 01 Dec 2020
Submitted by: Marcileia Zanatta
Definition: Ionic Liquids (ILs) are organic salts that melt commonly below 100 °C, constituted entirely by charged species. The tunability and versatility of ILs have given rise to several applications at the academic and industrial levels. Here the following topics are highlighted: chemical structure; ILs classification according to the possibility of proton transfer, and the historical generations of ILs.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 15 Mar 2021
Submitted by: Enrico Soldati
Definition: Bone microarchitecture has been shown to provide useful information regarding the evaluation of skeleton quality with an added value to areal bone mineral density, which can be used for the di-agnosis of several bone diseases. Bone mineral density estimated from dual-energy x-ray absorp-tiometry (DXA) has shown to be a limited tool to identify patients’ risk stratification and therapy delivery. Magnetic resonance imaging (MRI) has been proposed as another technique to assess bone quality and fracture risk by evaluating the bone structure and microarchitecture.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 10 Dec 2020
Submitted by: Włodzimierz Makulski
Definition: In recent years, we have seen spectacular growth in the experimental and theoretical investigations of magnetic properties of small subatomic particles: electrons, positrons, muons, and neutrinos. However, conventional methods for establishing these properties for atomic nuclei are also in progress, due to new, more sophisticated theoretical achievements and experimental results performed using modern spectroscopic devices. In this review, a brief outline of the history of experiments with nuclear magnetic moments in magnetic fields of noble gases is provided. In particular, nuclear magnetic resonance (NMR) and atomic beam magnetic resonance (ABMR) measurements are included in this text. Various aspects of NMR methodology performed in the gas phase are discussed in detail. The basic achievements of this research are reviewed, and the main features of the methods for the noble gas isotopes: 3He, 21Ne, 83Kr, 129Xe, and 131Xe are clarified. A comprehensive description of short lived isotopes of argon (Ar) and radon (Rn) measurements is included. Remarks on the theoretical calculations and future experimental intentions of nuclear magnetic moments of noble gases are also provided.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 18 Feb 2021
Submitted by: Kihwan Choi
Definition: Quantitative nuclear magnetic resonance (qNMR) has been used as a purity determination method for reference material development, and many related measurement techniques have been designed to acquire accurate and reliable results.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 27 Oct 2020
Submitted by: Poul Erik Hansen
Definition: Salt bridges are interactions, electrostatic combined with hydrogen bonding, between oppositely charged residues, typically carboxylic acid anions and ammonium ions, provided they are close together. For an illustration see Fig. 1.Salt bridges are of particular interest in proteins and other biomolecules. In the present contribution salt bridges are investigated by means of 1H chemical shifts, determination of pKa values and deuterium isotope effect on 15N and 1H chemical shifts. In the latter case model compounds like ammonium ions are also investigated and the use of deuterium isotope effects on chemical shifts are supported by Density Functional Theory (DFT) calculations. The use of isotope effects on chemical shifts enables a distinction between salt bridges observed in the solid state by X-ray diffraction and those actually present in solution.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 23 Feb 2021
Submitted by: Gaia Cartocci
Definition: In the context of child abuse spectrum, abusive head trauma (AHT) represents the leading cause of fatal head injuries in children less than 2 years of age. Immature brain is characterized by high water content, partially myelinated neurons, and prominent subarachnoid space, thus being susceptible of devastating damage as consequence of acceleration–deceleration and rotational forces developed by violent shaking mechanism. Diagnosis of AHT is not straightforward and represents a medical, forensic, and social challenge, based on a multidisciplinary approach. Beside a detailed anamnesis, neuroimaging is essential to identify signs suggestive of AHT, often in absence of external detectable lesions. Magnetic resonance imaging (MRI) represents the radiation-free modality of choice to investigate the most typical findings in AHT, such as subdural hematoma, retinal hemorrhage, and hypoxic-ischemic damage and it also allows to detect more subtle signs as parenchymal lacerations, cranio-cervical junction, and spinal injuries.
Entry Collection : Nuclear Magnetic Resonance
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Topic review
Updated time: 08 Jan 2021
Submitted by: Célia S. Bonnet
Definition: Zinc and copper are essential cations involved in numerous biological processes; and variations in their concentrations can cause diseases; such as neurodegenerative diseases; diabetes and cancers. Hence, the detection and quantification of these cations is of utmost importance for the early diagnosis of disease. MRI responsive contrast agents (mainly Lanthanide 3+ complexes), relying on a change in state of the MRI active part upon interaction with the cation of interest e.g. switch ON/OFF or vice versa, have been successfully utilized to detect zinc and are now being developed to detect Copper(II). These paramagnetic probes mainly exploit the relaxation-based properties (T1-based contrast agents), but also the paramagnetic induced hyperfine shift properties (paraCEST and parashift probes) of the contrast agents. The challenges encountered going from zinc to copper(II) detection are discussed. Depending on the response mechanism, the use of fast-field cycling MRI seems promising to increase the detection field while keeping a good response. In vivo applications of cation responsive MRI probes are only at their infancy and the recent developments are described, along with the associated quantification problems.
Entry Collection : Nuclear Magnetic Resonance
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