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核磁共振(NMR)文献文集

本文集包含50篇核磁共振(NMR)文献资料,NMR(Nuclear Magnetic Resonance)为核磁共振。是磁矩不为零的原子核,在外磁场作用下自旋能级发生塞曼分裂,共振吸收某一定频率的射频辐射的物理过程。核磁共振波谱学是光谱学的一个分支,其共振频率在射频波段,相应的跃迁是核自旋在核塞曼能级上的跃迁。

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核磁共振(NMR)文献文集 文档列表

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A Comparison of Induction-Detection NMR and ForceDetection NMR on Micro-NMR Device Design
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Nuclear Magnetic Resonance (NMR) is widely used in medical diagnostics and chemicalanalysis. Due to rapid growing of the NMR applications, the conventional NMR systemsmay not fulfill the need of all applications. The development of a micro-NMR devicewould not only benefit the original NMR applications but could also open a door for newNMR applications. Two approaches for building a NMR system, Induction-DetectionNuclear Magnetic Resonance (IDNMR) and Force-Detection Nuclear MagneticResonance (FDNMR) are explored and compared in this paper. The comparison resultshows that the FDNMR approach outperforms the IDNMR approach in signal-to-noiseratio when the sample radius is below 410 μm for protons and 1900 μm for chlorides. This suggests that the FDNMR approach is more appropriate for making the micro-NMRdevice.
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A REVIEW OF THE ELEMENTS OF NUCLEAR MAGNETIC RESONANCE INSTRUMENTATION
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:The early efforts to detect nuclear magnetic resonance (NMR) when reviewed, carries a valuablemessage on how to go about making discoveries of phenomena on the basis of what is known already. Particularly the instrumentation is an effort which has an outlook on enterprises that provide various laboratoryequipments and assembling these units in a way that brings out precisely what is being looked for is a creativepreoccupation in scientific research. The kind of home-built spectrometers which have been used by everyresearcher for the achievements in the NMR spectroscopic technique is an example of the materialmanipulation to improve stage by stage thoughtfully knowing what went on before. Thus the review would haveeducative value while revealing the lessons on scientific matter studied. NMR of the current days is aplenty withcommercial spectrometers which have unimaginable features built in and produce high quality spectraautomatically without the user having to know much about the settings. Essentially black-box approach to theuse of the spectrometers makes possible strides in leaps and jumps in a wide variety of disciplines of study. Onthe other hand the early efforts have been more educative on the equipments and instrumentation aspects. Theresearchers themselves had a hand on laboratory exercise to make the equipment for what they have to researchon. In this contrasting situation a review of the early days NMR instrumentation is provided in this article for thebenefit of student community to find an occupation while innovating their learning methods. Descriptions in thisarticle are oriented towards school and college standards so as to inspire the readers to look for more oninstrumental methods and grasp the recent advances quickly and confidently in these days of convenientlyautomated and much simplified ?black-box? approach to use of instruments. An important point to mention isthat the circuit diagrams given in this articles are the author?s original version of block diagrams or schemessimilar to concept diagrams (pedagogically speaking) to introduce newly certain topics. Hence the studentsshould not expect to plug in working circuits to see the functions. Note carefully that no specific componentvalue is given nor any model numbers to commercially available components – even the circuit elements are notcopied ones but drawn by the author with MS WORD drawing tools.
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accurate and inexpensive NMR auto tune and match system
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:We introduce a low complexity, low cost, yet sufficiently accurate automatic tune and match system for NMRand MRI applications. The ArduiTaM builds upon an Arduino Uno embedded system that drives a commercial frequencysynthesizer chip to perform a frequency sweep around the Larmor frequency. The generated low power signal is fed to theNMR coil, after which the reflected waves are detected using a directional coupler, and amplified. The signal shape is then5 extracted by means of an envelope detector and passed on to the Arduino, which performs a dip search while continuouslygenerating actuator control patterns to adjust the tune and match capacitors. The process stops once the signal dip reaches theLarmor frequency. The ArduiTaM works readily with any spectrometer frequency in the range from 1 T to 23 T. The speedof ArduiTaM is mainly limited by the clock of the Arduino, and the capacitor actuation mechanism. The Arduino can easilybe replaced by a higher speed micro controller, and varactors can replace stepper-motor controlled variable capacitors. The10 ArduiTaM is made available in open source, so it is easily duplicated.
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Advances in Electronics Prompt a Fresh Look at Continuous Wave (CW) Nuclear Magnetic Resonance (NMR)
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:: Continuous Wave Nuclear Magnetic Resonance (CW-NMR) was a popular method forsample interrogation at the birth of magnetic resonance but has since been overlooked by most infavor of the now more popular pulsed techniques. CW-NMR requires relatively simple electronicsalthough, for most designs, the execution is critical to the successful implementation and sensitivityof the system. For decades there have been reports in the literature from academic groups showingthe potential of magnetic resonance relaxation time measurements in industrial applications suchas the production of food and drink. However, the cost, complexity and power consumptionof pulsed techniques have largely consigned these to the literature. Advances in electronics anddevelopments in permanent magnet technology now require a fresh look at CW-NMR to see if itis capable of providing cost effective industrial solutions. In this article, we review the electronicsthat are needed to undertake a continuous wave NMR experiment starting with early designs andjourneying through the literature to understand the basic designs and limitations. We then reviewthe more recent developments in this area and present an outlook for future work in the hope thatmore of the scientific community will take a fresh look at CW-NMR as a viable and powerful low-costmeasurement technique.
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Analysis of ringing effects due to magnetic core materials in pulsed nuclear magnetic resonance circ
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:This work presents investigations and detailed analysis of ringing in a non-resonant pulsednuclear magneticresonance (NMR) circuit. Ringing is a commonly observed phenomenon in high power switching circuits. The oscillations described as ringing impede measurements in pulsed NMR systems. It is therefore desirablethat those oscillations decay fast. It is often assumed that one of the causes behind ringing is the role of themagnetic core used in theantenna (acting as an inductive load). We will demonstrate that an LRC subcircuit isalso set-up due to the inductive load and needs to be considered due to its parasitic effects. It is observed thatthe parasitics associated with the inductive load become important at certain frequencies. The outputresponse can be related to the response of an under-damped circuit and to the magnetic core material. Thisresearch work demonstrates and discusses ways of controlling ringing by considering interrelationshipsbetween different contributing factors.
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Applications of NMR to structure-based drug design in structural genomics
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Structural genomics is poised to have a tremendous impact on traditional structure-based drug design programs. As a result, there is a growing need to obtain rapid structural information in a reliable form that is amenable torational drug design. In this manner, NMR has been expanding and evolving its role in aiding the design process. A variety of NMR methodologies that cover a range of inherent resolution are described in the context of structure-based drug design in the era of structural genomics.
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Basic NMR Concepts A Guide for the Modern Laboratory
标签:NMR核磁共振成像
积分:1 类型:技术书籍上传者:太白金星上传时间:2021-08-31
简介:This handout is designed to furnish you with a basic understanding of Nuclear MagneticResonance (NMR) Spectroscopy. The concepts implicit and fundamental to the operationof a modern NMR spectrometer, with generic illustrations where appropriate, will bedescribed. It can be read without having to be in front of the spectrometer itself. Somebasic understanding of NMR spectroscopy is assumed.
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Beta‐detected Nuclear Magnetic Resonance (β‐NMR) Towards Depth Resolved NMR
标签:NMR核磁共振成像
积分:1 类型:教程及课件上传者:太白金星上传时间:2021-08-31
简介:NMR • Beta detected NMR – Comparison to NMR – Detection – Measurement methods • Examples from β‐NMR • Challenges • Conclusions
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Comparing two Power Supplies for Fast-Field Cycling Nuclear
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:The main power supply of a Fast Field-CyclingNuclear Magnetic Resonance (FFC-NMR) is the key elementcomparing the performance of different solutions. The powersupply is a current source that supplies a magnet being thecurrent controlled in order to perform adjustable and repetitivecurrent cycles. This power supply can be based on differenttopologies, operating principles and controlled using distincttechniques. If for the final users of this experimental techniquethe current cycles of the equipment is the core feature, for thedevelopers also the power losses distribution needs to be analyzedin order to develop efficient solutions. In this paper, the powerlosses and the dynamic behavior of two solutions for the FFCNMR power supply are compared and discussed.
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CMOS RF Biosensor Utilizing Nuclear Magnetic Resonance
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:We report on a CMOS RF transceiver designed fordetection of biological objects such as cancer marker proteins. Its main function is to manipulate and monitor RF dynamics ofprotons in water via nuclear magnetic resonance (NMR). Targetobjects alter the proton dynamics, which is the basis for ourbiosensing. The RF transceiver has a measured receiver noisefigure of 0.7 dB. This high sensitivity enabled construction of anentire NMR system around the RF transceiver in a 2-kg portableplatform, which is 60 times lighter, 40 times smaller, yet 60 timesmore mass sensitive than a state-of-the-art commercial benchtopsystem. Sensing 20 fmol and 1.4 ng of avidin (protein) in a 5 Lsample volume, our system represents a circuit designer’s approach to pursue low-cost diagnostics in a portable platform.
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Comparing the Power Losses of Power Supplies for Fast-Field Cycling Nuclear Magnetic Resonance Equip
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介: The main feature of the Fast-Field Cycling (FFC)Nuclear Magnetic Resonance (NMR) power supplies is to drivea controlled current fulfilling the requirements of this technique. This feature allows fast switching the current of the FFCmagnet and performing accurate and repetitive current cycles. When designing this equipment the power losses is not afundamental parameter of the optimization process but areestimated in order to validate the topology of the final solutiongiving that the efficiency of the power solution influences thepower consumption, and therefore the operational costs, whichshould be minimized. Under this context, from the power efficiency viewpoint, thepower losses of two possible solutions are compared anddiscussed in this paper. Typical FFC current cycles are used asreference in order to balance the pros and cons of bothsolutions.
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Continuous wave nuclear magnetic resonance estimation of spin-system properties from steady-state tr
标签:NMR核磁共振成像
积分:1 类型:技术书籍上传者:太白金星上传时间:2021-08-31
简介:Magnetic resonance imaging (MRI) is a powerful imaging modality, widely used in routine clinicalpractice and as an investigational tool in basic science. The contrast in MRI is related to boththe underlying tissue properties, which undergo disease or injury related changes, and to the MRImethod and sequence parameters used. It is the latter with which this thesis is concerned: the designand implementation of novel MRI acquisition paradigms and associated reconstruction methods. The majority of MRI methods excite the object of interest with a series of short RF pulses, varyingthe weaker spatial magnetic field using the gradients, and ensuring the RF transmitter is inactivewhile acquiring a series of decaying MR signals. This regime linearises the inherently nonlinearbehaviour of a magnetic resonance spin-system, allowing the acquired signals to be considered in aspatial frequency space and an image to be reconstructed using the well known Fourier transform. It is our assertion that nonlinear behaviour of the magnetic spin signal will lead to advantageousattributes in future MR methods, just as moving beyond conventional linear spatial gradients tononlinear encoding fields led to methods for accelerated imaging and variable spatial resolution. Reconstruction of spin-system properties from nonlinear MR signals requires algorithms beyondthe Fourier transform. In this thesis we propose spectroscopy, radial projection imaging and relaxometry methods as optimisation problems which minimise the mismatch between experimentalmeasurements and predictions from Bloch equation based signal models. The use of continuouswave (CW) excitation patterns allows the development of signal models which are computationallyefficient as they rely on analytical solutions of the Bloch equations or matrix inversion via harmonicbalancing, rather than numerical integration. Ultra-short relaxation methods have been applied to a range of applications and demonstrate thatMRI is finding use in areas far beyond traditional soft-tissue imaging. Soft tissues have an easilyobservable long duration MR signal, whereas the signal decays rapidly for harder tissues such asbone, or in regions that distort the magnetic field due to magnetic susceptibility gradients, such asthe lungs. Rabi modulated CW techniques operating in a fully continuous mode have the potentialto measure ultra-short relaxation signals in a similar range to ‘true’ zero echo time techniques. Work inspired by quantum optics has shown that exciting a spin-system with a long duration Rabimodulated RF field leads to a significant steady-state MR signal. The steady-state trajectory ishighly nonlinear and can be expressed as a series of harmonics of the amplitude modulation frequency of the RF field. This harmonic response provides a natural decoupling of the excitationand measurement bandwidth, and the ability to maintain a steady-state response under low powerexcitation reduces the isolation requirements between hypothetical transmit and receive chains. Our experimental investigation of steady-state trajectories makes use of two pseudo-simultaneousexcitation and measurement protocols. Whilst these methods were adequate to explore the proof-ofconcept applications, hardware modifications are suggested to unlock the full potential of continuouswave excitation patterns. This thesis demonstrates that CW excitation patterns allow the construction of efficient predictionmodels and elicit an information-rich steady-state response from which underlying spin-system properties can be reconstructed. It is anticipated that further development of these concepts and relatedhardware modifications will lead to new continuous wave imaging paradigms.
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De novo NMR pulse sequence design using Monte-Carlo optimization techniques
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Separated Local Field (SLF) experiments have been routinely used for measuring 1H-15N heteronucleardipolar couplings in oriented-sample solid-state NMR for structure determination of proteins. In theon-going pursuit of designing better-performing SLF pulse sequences (e.g. by increasing the number ofsubdwells, and varying the rf amplitudes and phases), analytical treatment of the relevant averageHamiltonian terms may become cumbersome and/or nearly impossible. Numerical simulations of NMRexperiments using GPU processors can be employed to rapidly calculate spectra for moderately sized spinsystems, which permit an efficient numeric optimization of pulse sequences by the Monte CarloSimulated Annealing protocol. In this work, a computational strategy was developed to find the optimalphases and timings that substantially improve the 1H-15N dipolar linewidths over a broad range of dipolar couplings as compared to SAMPI4. More than 100 pulse sequences were developed de novo and testedon an N-acetyl Leucine crystal. Seventeen distinct pulse sequences were shown to produce sharper meanlinewidths than SAMPI4. Overall, these pulse sequences have more variable parameters (involving nonquadrature phases) and do not involve symmetry between the odd and even dwells, which would likelypreclude their rigorous analytical treatment. The top performing pulse sequence, termed ROULETTE-1,has 18% sharper mean linewidths than SAMPI4 when run on an N-acetyl Leucine crystal. This sequencewas also shown to be robust over a broad range of 1H carrier frequencies and various crystal orientations. The performance of such an optimized pulse sequence was also illustrated on 15N Leucine-labeled Pf1coat protein reconstituted in magnetically aligned bicelles. For the optimized pulse sequence the meanpeak width was 14% sharper than SAMPI4, which in turn yielded a better signal to noise ratio, 20:1 vs. 17:1. This method is potentially extendable to de novo development of a variety of NMR experiments
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Design of High Performance Scroll Microcoils for Nuclear Magnetic Resonance Spectroscopy of Nanolite
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:The electromagnetic properties of scroll microcoils are investigated with finite elementmodelling (FEM) and the design of experiment (DOE) approach. The design of scroll microcoils wasoptimized for nuclear magnetic resonance (NMR) spectroscopy of nanoliter and subnanoliter samplevolumes. The unusual proximity effect favours optimised scroll microcoils with a large number ofturns rolled up in close proximity. Scroll microcoils have many advantages over microsolenoids:such as ease of fabrication and better B1-homogeneity for comparable intrinsic signal-to-noise ratio(SNR). Scroll coils are suitable for broadband multinuclei NMR spectroscopy of subnanoliter sample.
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Design, principles and building blocks of Design, principles and building blocks of heteronuclear he
标签:NMR核磁共振成像
积分:1 类型:教程及课件上传者:太白金星上传时间:2021-08-31
简介:Contents Contents • Heteronuclear Heteronuclear NMR: motivation NMR: motivation • Basic pulse sequence elements and 2D correlations Basic pulse sequence elements and 2D correlations • RF pulses: calibration, selective pulses RF pulses: calibration, selective pulses • Sensitivity enhancement, grad Sensitivity enhancement, gradients, coherence selection ients, coherence selection • Water-flip back flip back • Spin-state selection, TROSY state selection, TROSY • Triple resonance experiments Triple resonance experiments •Isotope editing and filtering
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Development and Applications of a Low-Field Portable NMR System
标签:NMR核磁共振成像
积分:1 类型:技术书籍上传者:太白金星上传时间:2021-08-31
简介:Nuclear magnetic resonance (NMR) is a phenomenon similar to MRIin which radio frequency signals are used to excite and manipulate atomicnuclei within a static magnetic field. Following excitation, the nuclei returnto equilibrium, all the while offering valuable molecular level informationpertaining to the sample. Within the last decade, the development of small and inexpensive NMRspectrometers and permanent magnet NMR sensors has been a significantfocus within the NMR community. More recently, application scientists havesought practical applications for the new technologies. In this thesis, a prototype NMR apparatus consisting of a spectrometerand 3.2MHz permanent magnet sensor was extended to enable scientificmeasurements. This involved developing radio frequency electronic circuitryfor the spectrometer front-end, and electromagnetic noise shielding and tem-perature regulation for the magnetic sensor. Experimental results confirmedthat repeatable measurements using the modified apparatus were indeedpossible. The NMR apparatus was thereafter successfully used to study flow,diffusion and kiwifruit using several different experimental techniques. Asignificantly larger effort was then expended upon the study of T2 relaxation inpectin model systems using pH as the adjustable parameter. The fascinatingexperimental results were successfully interpreted and modeled across threepH zones in terms of a proton chemical exchange model and molecularconformational changes. In addition, it was found that pectin carboxylde-protonation was significantly less than expected. Further experimentsperformed upon galacturonic acid monomers, dimers and trimers appearedto further illuminate the pectin results. Future experiments are planned. Also while studying pectin solutions, an unexpected pH-dependent watertransverse relaxation behavior was observed at both 3.2MHz and 400MHz. The only references found in the literature were from a small publicationalmost 50 years ago, and a 2011 publication. Altogether, this thesis contributed to original knowledge in several ways:it showed how a low-field apparatus and single-sided sensor could be im-proved and utilized for a variety of scientific measurements; it showed bothexperimentally and theoretically how T2 for pectin solutions change withpH; it revealed an unexpected de-protonation limit for pectin molecules; itrevealed a T2 pH dependence for water
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Development of portable low field NMR magnet Design and construction
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:法语文献: 本文的工作主要集中在便携式核磁共振(NMR)系统磁体的设计、建模和仿真,然后进行实现和验证。
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EARTHS FIELD NUCLEAR MAGNETIC RESONANCE
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:When a proton is placed in an external magnetic field, its magnetic moment will attempt to align with the magnetic field. It will fail to completely align due to thermal motion and the spin angular momentum which causes the magnetic moment to precess, or spin, around the magnetic field. If that external magnetic field is then suddenly turned off, the proton will start to precess around the only other magnetic field available: the Earth’s. This precession towards alignment with the Earth’s magnetic field can be measured and used to calculate the Spin Relaxation Time (T2). The T2 value is a time constant with which “the magnetization and signal decay towards zero.” [1](see figure 1.1) This time constant will change if other materials are brought near the sample, and this change can tell us about the magnetization of the other materials.
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FORCE-GRADIENT DETECTED NUCLEAR MAGNETIC RESONANCE AND THE ORIGINS OF NONCONTACT FRICTION
标签:NMR核磁共振成像
积分:1 类型:技术书籍上传者:太白金星上传时间:2021-08-31
简介:布洛赫教授告诉过你如何在一滴水中探测到磁原子核的进动。尽管这样的实验在我们的实验室里已经司空见惯,但我还没有失去一种惊奇和喜悦的感觉,即这种微妙的运动应该存在于我们周围的所有普通事物中,只向寻找它的人展示它自己。我记得,就在七年前我们第一次实验的冬天,用新的眼睛观察雪。那里的雪覆盖着我的门前台阶——巨大的质子堆在地球磁场中静静地前进。把这个世界看作是一个丰富而奇怪的东西,这是许多发现的私人回报。但我担心这与我们作为物理学家必须问自己的一个严肃问题没有什么关系:我们能从这一切中学到关于物质结构的什么? Professor Bloch has told you how one can detect the precession of the mag- netic nuclei in a drop of water. Commonplace as such experiments have become in our laboratories, I have not yet lost a feeling of wonder, and of delight, that this delicate motion should reside in all the ordinary things around us, revealing itself only to him who looks for it. I remember, in the winter of our first experiments, just seven years ago, looking on snow with new eyes. There the snow lay around my doorstep - great heaps of protons quietly precessing in the earth‘s magnetic field. To see the world for a moment as something rich and strange is the private reward of many a discovery. But I am afraid it has little bearing on the sober question we must, as physicists, ask ourselves: What can we learn from all this about the structure of matter?
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fundamentals of nuclear magnetic resonance
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:The top will precess about the direction of the gravitational eld, with a characteristic frequency determined by parameters such as the mass, moments of inertia and the gravitational...
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IRVINE Design and Construction of a Four-Channel 1H13C2H15N 800 MHz MAS ss-NMR Probe DISSERTATION
标签:NMR核磁共振成像
积分:1 类型:应用文档上传者:太白金星上传时间:2021-08-31
简介:Determining the structure of proteins is an area of great scientific interest. Their ability to perform their specific biological functions is primarily a result of their specific folded structure, which is difficult if not impossible to predict even when the exact sequence of component nucleic acids is known. Misfolding of proteins can result in health problems such as cataract formation, Alzheimers disease, Type II diabetes, ALS, and many others [1]. Knowledge of both normal and misfolded protein structure can help in understanding both the mechanisms that underlie these conditions and in the design of drugs to work with specific proteins. Another intriguing but difficult area of investigation is the determination of the structure of integral membrane protieins. To determine membrane protein structure in the biologically relevant conformation, a membrane mimetic such as bicelles composed of DMPC/DHPC lipids can be used [2].
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Low-field Classroom Nuclear Magnetic Resonance System
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:The goal of this research was to develop a Low-field Classroom NMR system that will enable hands-on learning of NMR and MRI concepts in a Biological-Engineering laboratory course. A permanent magnet system, designed using finite-element modeling software, was built to produce a static field of B~ 0 = 0.133 Tesla. A single coil was used for both transmitting the excitation pulses and detecting the NMR signal. The probe circuit is essentially an LC tank with a tunable resonant frequency. An FPGA is used to produce the excitation pulses and process the received NMR signals. This research has led to the ability to observe Nuclear Magnetic Resonance. ‘SpinLattice’ and ‘Spin-Spin’ relaxation times of glycerin samples can easily be measured. Future work will allow further MRI exploration by incorporating gradient magnetic field coils.
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MAGNETIC RESONANCE TECHNIQUES
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:First the main characteristics of the NMR magnetic measurements,such as accuracy, independence of field direction and zerotemperature coefficient are recalled. Then some different magneticfield measuring techniques using NMR, and the conditions to achievesuch measurements, are described. Finally, recent NMR applications,used in various domains such as MRI and accelerator-magnetalignment, are described.
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Nuclear Magnetic Resonance (NMR) Spectroscopy for the In Situ Measurement of Vapor−Liquid Equilibria
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Vapor?liquid equilibrium (VLE) data (T, p, x, y) arevital for the development of mixture thermodynamic models. Herein, we demonstrate the use of nuclear magnetic resonance(NMR) spectroscopy as an in situ method for VLE measurements. The experiment is carried out entirely inside the NMR sample tube. The simultaneous measurement of liquid- and vapor-phasecomposition was achieved by the insertion of a sealed glass capillaryinto the NMR sample tube. In this way, a small amount of the liquidphase wicks into the wedge-shaped gap between the capillary andthe inner wall of the NMR tube. The presence of a suspended liquidmeniscus was confirmed by X-ray computed tomography, and itsbehavior was examined by computational fluid dynamics. Thecomponents of the two phases are observed as distinct signals in the NMR spectra. The temperature-dependent spectrum ofmethanol, contained in a sealed capillary, was used to measure the temperature. Vapor density was measured instead of pressure; thiswas accomplished by calibration with gas-phase ethane at known densities. With this approach, we provide proof-of-concept resultsat 291.2 K on binary mixtures of (R32 + R125), (R125 + R143a), (ethane + neopentane), and (ethane + benzene).
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Nuclear Magnetic Resonance (NMR)
标签:NMR核磁共振成像
积分:1 类型:教程及课件上传者:太白金星上传时间:2021-08-31
简介:Introduction – What is NMR Good Gor? • Brief Theory – Quantum Chemistry, Magnetization • NMR Concepts – – Frequency, Relaxation, Chemical S hift, Coupling, Integration • 1-Dimension NMR Experiments • 2-D NMR – COSY, HMQC/HSQC, NOESY • ********************BREAK************************* • Biom olecular NMR – 3-D • NMR Application Examples – Dynamic NMR, Solid State NMR, Inorganic, Diffusion • Spectrometer Description – Probes and Gradients • Structure Determination with NMR
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Nuclear Magnetic Resonance Chem 634 T. Hughbanks
标签:NMR核磁共振成像
积分:1 类型:教程及课件上传者:太白金星上传时间:2021-08-31
简介:NMR is Broadly Applicable • Nuclear Magnetic Resonance • Applies to atoms and molecules with nuclear spin quantum numbers greater than zero. • Applied magnetic field induces Zeeman splittings in spin states, and energy is absorbed from radiation when the frequency meets the resonance condition, hν = ∆E ∝ µN × H0 • 1/λ ~ 10–3 cm–1 , ν = c/λ ~ 25–500 MHz
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Nuclear Magnetic Resonance for the People
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Since NMR was first demonstrated in condensed matter in 1945, the technique has experienced tremendous growth. NMR was commercialized in the 1960’s and by the end that decade NMR was routinelyused as a central tool by synthetic organic chemists. Compared to other spectroscopies NMR spectra are Figure 1.1: 1H-decoupled 13C NMR spectrum of Cholesterol. There are 26 resonances in this spectrum,which when numbered from left to right, are assigned to the corresponding numbered carbon atom inCholesterol based on its resonance frequency.
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Nuclear Magnetic Resonance in pulsed high magnetic fields
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:德语文献:H?chste Magnetfelder haben sich zu einem unverzichtbaren Werkzeug der Festk?rperphysikentwickelt. Sie werden insbesondere verwendet, um die elektronischen Eigenschaften vonmodernen Materialien zu erforschen. Da Magnetfelder oberhalb von 45 Tesla nicht mehrmit statischen (z.B. supraleitenden) Feldern zu erreichen sind, haben sich weltweit verschiedene Labore auf die Erzeugung gepulster Magnetfelder mit angestrebten Maximalwerten von 100 Tesla spezialisiert. In der vorliegenden Arbeit werden Anwendungsm?glichkeiten der kernmagnetischen Resonanz (NMR) in gepulsten Magnetfeldern aufgezeigt. Es ist gelungen, die starke Zeitabh?ngigkeit der gepulsten Magnetfelder mittels NMR pr?zise zu vermessen. Die genaueKenntnis des Magnetfelds nach dem Puls erm?glicht, die Zeitabh?ngigkeit aus den Datenzu entfernen, sodass auch eine koh?rente Signal-Mittelung m?glich ist. Davon ausgehendwerden erstmalig Messungen der chemischen Verschiebung, der Knight Shift, der SpinGitter-Relaxationsrate 1/T1 und der Spin-Spin-Relaxationsrate 1/T2 diskutiert. Schlie?lich werden die im Zusammenhang mit gepulsten Magnetfeldern erarbeiteten Gleichungen in vereinfachter Form zur genauen Messung und Analyse des freien InduktionsZerfalls von 19F Kernspins in Calciumfluorid verwendet. Durch Messung des Zerfallsüber sechs Gr??enordnungen wird eine genaue Analyse bezüglich einer neuartigen Theorie erm?glicht, welche den Zerfall basierend auf der Annahme mikroskopischen Chaos’erkl?rt. Diese Theorie hat das Potenzial, zu einem tieferen Verst?ndnis von Quantenchaosin makroskopischen Vielteilchensystemen zu führen.
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Nuclear Magnetic Resonance Some atomic nuclei possess angular momentum also referred to as spin. Thi
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Some atomic nuclei possess angular momentum also referred to as spin. This is given the quantum # I which can have integer and half integer values.
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Nuclear Magnetic Resonance Spectroscopy
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Nuclear magnetic resonance (NMR) spectroscopy is based on the measurement of absorption of electromagnetic radiation in the radiofrequency region of roughly 4 to 900 MHz. In contrast to ultraviolet (UV), visible, and infrared (IR) absorption, nuclei of atoms rather than outer electrons are involved in the absorption process. Furthermore, to cause nuclei to develop the energy states required for absorption to occur, it is necessary to place the analyte in an intense magnetic field. In this chapter we describe the theory, instrumentation, and applications of NMR spectroscopy. NMR spectroscopy is one of the most powerful tools available to chemists and biochemists for elucidating the structure of chemical species. The technique is also useful for the quantitative determination of absorbing species. NMR spectroscopy is one of the few instrumental methods applicable to solids, liquids, and gases.
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Nuclear Magnetic Resonance
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:What we call “nuclear magnetic resonance” (NMR) was developed simultaneously but independently by Edward Purcell and Felix Bloch in 1946. The experimental method and theoretical interpretation they developed is now called “continuous-wave NMR” (CWNMR). A different experimental technique, called “pulsed NMR” (PNMR), was introduced in 1950 by Erwin Hahn. Pulsed NMR is used in magnetic resonance imaging (MRI). Purcell and Bloch won the Nobel Prize in Physics in 1952 for NMR; more recently NMR was the subject of Nobel Prizes in Chemistry in 1991 and 2002. We have both NMR setups in the advanced labs: one is a variation of the CWNMR method, and the other is a pulsed NMR system. The physics underlying NMR is the same for both the continuous and pulsed methods, but the information obtained may be different. Certainly, the words used to describe what is being done in the experiments are different. In continuous-wave NMR one tunes a weak radio-frequency oscillator to match the natural frequency of nuclear magnetic moments precessing in a static magnetic field. When the frequencies match, the moments “resonate” and energy transfer between the RF field and the sample is optimized; this resonance creates an electrical signal in a pickup coil. By sweeping the magnetic field, one can leave the RF frequency fixed but tune the resonance itself to excite the sample and then see how quickly the the magnetization dies away by watching a “beat pattern.” In pulsed NMR, one applies a sequence of strong RF bursts or “pulses” to the sample that are very short in duration. The resulting signal, called the “free induction” is then optimized to tune the RF oscillator. The pulses are strong enough and short enough to reorient all of the spins in a coherent way. One can flip the magnetization upside down with a “π-pulse” (180 degrees) or sideways with a “π/2-pulse” (90 degrees). With the a sequence of pi-pulses, one can create the fascinating phenomenon of “spin echoes.” More on the two methods is given later in this introduction.
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Nuclear Magnetic Resonance2
标签:NMR核磁共振成像
积分:1 类型:技术书籍上传者:太白金星上传时间:2021-08-31
简介:Pieter Zeeman observed in 1896 the splitting of optical spectral lines in the field of an electromagnet. Since then, the splitting of energy levels proportional to an external magnetic field has been called the \"Zeeman effect\". The \"Zeeman resonance effect\" causes magnetic resonances which are classified under radio frequency spectroscopy (rf spectroscopy). In these resonances, the transitions between two branches of a single energy level split in an external magnetic field are measured in the megahertz and gigahertz range. In 1944, Jevgeni Konstantinovitch Savoiski discovered electron paramagnetic resonance. Shortly thereafter in 1945, nuclear magnetic resonance was demonstrated almost simultaneously in Boston by Edward Mills Purcell and in Stanford by Felix Bloch. Nuclear magnetic resonance was sometimes called nuclear induction or paramagnetic nuclear resonance. It is generally abbreviated to NMR. So as not to scare prospective patients in medicine, reference to the \"nuclear\" character of NMR is dropped and the magnetic resonance based imaging systems (scanner) found in hospitals are simply referred to as \"magnetic resonance imaging\" (MRI)
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PARAMETRICALLY NUCLEAR SPECTROMETER ARAMETRICALLY-ENHANCED UCLEAR MAGNETIC RESONANCE PECTROMETER PRO
标签:NMR核磁共振成像
积分:1 类型:技术书籍上传者:太白金星上传时间:2021-08-31
简介:Nuclear magnetic resonance (NMR) is a phenomenon discovered relatively recentlyin 1945, and has revolutionized medical imaging and chemical analysis since. Nuclei withnon-zero spin, such as protons, have an intrinsic magnetic moment and spin angularmomentum that can be manipulated using an externally applied static magnetic field.\r\nNuclear spins preferentially align with the static magnetic field DE to lower their energystate, resulting in a bulk spin magnetization in the field direction. When an appropriateoscillating magnetic pulse is applied, the nuclear spins can be reoriented perpendicular tothe direction of DE. Because of their intrinsic spin angular momentum, nuclear spinsprecess about DE before dephasing and returning to equilibrium parallel to the direction ofthe static magnetic field. This phenomenon is termed Larmor precession. Using a sensitivemagnetic coil perpendicular to DE, the precessing magnetization from the nuclear spins canbe detected. The properties of the signal, such as relaxation time, can be used tocharacterize the sample under analysis. [1]The high cost of the equipment to generate the intense static magnetic field,however, has been a major deterrent to the widespread adoption of NMR technology. Thehomogeneity of DE is directly related to the spectral resolution of the NMR signal, whichalso contributes to the cost. The Bruker BioSpin AVANCE 1000 NMR spectrometer, whichincorporates the world’s strongest superconducting NMR magnet at 23 T, has a list price of11.7 million Euros. [2]The Earth produces a magnetic field that can be utilized as the static magnetic fieldin NMR measurements, in lieu of an externally generated magnetic field. The strength of theEarth’s magnetic field varies approximately from 30 μT near the equator to 60 μT near thegeomagnetic poles. [3] The strength of the Earth’s magnetic field on the University ofBritish Columbia Vancouver campus (49°15'59", –123°15'13") is approximately 55 μT. [4]
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Permanent Magnet Based Magnetic Resonance Sensors
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:In 2006 patent EP2069769A2 described using magnetic resonance (MR), instead of fluorescence, as the detection method for microarrays. This covered the concept of binding magnetic particles, such as Superparamagnetic Iron Oxide (SPIO), to a surface in order to change the MR signal that would normally be expected from the fluid covering the surface to which the particles were bound. In this thesis, measurement techniques are presented, utilising both pulsed and continuous wave nuclear magnetic resonance (CWNMR), where surface bound magnetic nanoparticles disrupt the MR signal that would normally be detected in the fluid covering the surface, using low magnetic field sensors constructed from permanent magnets. A pulsed technique is presented with a sensor constructed using permanent magnets in a Halbach arrangement. Using a technique called Magnetic Resonance Disruption (MaRDi), it is shown that the T2 eff relaxation time of a test liquid, polydimethylsiloxane (PDMS), reduces as the proportion of the surface area covered with SPIO increases. In addition, a linear decrease in the signal amplitude from the PDMS as a function of SPIO coverage, which is observed both for an integral over 4096 NMR echoes and even just in the first echo. The latter result suggests the potential for a technique to be developed with simplified and low cost electronics. A CWNMR technique is also presented by revisiting the Look and Locker’s tone-burst experiments but modified to use a commercial marginal oscillator. Though observing the transient effect when a sweep coil is switched on, a parameter Tx can be determined that is related to relaxation time T1 that can subsequently be calculated with the aid of calibration samples. This Transient Effect Determination of Spin Lattice relaxation time (TEDSpiL) was automated using low cost microcontrollers. A potential industrial application of detecting moisture uptake through improperly stored dehydrated milk powder is also presented.
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Phil Lect1 instrum v3_ReducedSize
标签:NMR核磁共振成像
积分:1 类型:教程及课件上传者:太白金星上传时间:2021-08-31
简介:Phil Lect1 instrum v3_ReducedSize.pdf
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Physics of Magnetic Resonance
标签:NMR核磁共振成像
积分:1 类型:教程及课件上传者:太白金星上传时间:2021-08-31
简介:Physics of Magnetic Resonance • Magnetic Resonance Imaging – High resolution – High contrast – Tomographic – Non-invasive (non-ionizing) • Nuclear Magnetic Resonance (NMR) properties – Stimulated by magnetic fields and radio-frequency fields – Pulse sequences govern time varying application of these fields • Mainly for anatomy but can see function as well – Blood flow – Diffusion of water – Blood oxygenation: functional MRI (fMRI) for brain function
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PORTABLE AND AUTONOMOUS MAGNETIC RESONANCE
标签:NMR核磁共振成像
积分:1 类型:技术书籍上传者:太白金星上传时间:2021-08-31
简介:Nuclear magnetic resonance (NMR) is one of the most important tools for studyingmatter at the molecular level. Originally developed in the late 1940s and early 1950sindependently by the Purcell group at Harvard and the Bloch group at Stanford, NMRhas been heavily utilized in the physics and chemistry disciplines for studying physicaland molecular compositions of liquid samples. Since its inception, advancements inNMR technology has led to many new applications and uses being discovered, withthe arguably most well known application being magnetic resonance imaging (MRI). Other applications include investigation of porous media [4, 5], quality control for foodproducts [6, 7, 8], inspection of polymers [9, 10], the study of agricultural products[11], as well as many others [12, 13].
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Pulsed Nuclear Magnetic Resonance
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:To observe nuclear magnetic resonance, the sample nuclei are first aligned in a strong magnetic field. In this experiment, you will learn the techniques used in a pulsed nuclear magnetic resonance apparatus (a) to perturb the nuclei out of alignment with the field and (b) to measure the small return signal as the misaligned nuclei precess in the field. Because the return signal carries information about the nuclear environment, the technique has become widely used for material analysis. Initially, you will study the behavior of hydrogen nuclei in glycerin because the signal is easy to find and interpret. Samples involving other nuclei and other nuclear environments can also be investigated.
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Pulsed Nuclear Magnetic Resonance1
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:What we call “nuclear magnetic resonance” (NMR) was developed simultaneously but independently by Edward Purcell and Felix Bloch in 1946. The experimental method and theoreticalinterpretation they developed is now called “continuous-wave NMR” (CWNMR). A differentexperimental technique, called “pulsed NMR” (PNMR), was introduced in 1950 by Erwin Hahn. Pulsed NMR is used in magnetic resonance imaging (MRI). Purcell and Bloch won the NobelPrize in Physics in 1952 for NMR; more recently NMR was the subject of Nobel Prizes in Chemistry in 1991 and 2002. We have both NMR setups in the advanced labs: one is a variation ofthe CWNMR method, and the other is a pulsed NMR system. The physics underlying NMR is the same for both the continuous and pulsed methods, butthe information obtained may be different. Certainly, the words used to describe what is beingdone in the experiments are different: in the continuous-wave case one tunes a radio-frequencyoscillator to “beat” against the resonance of a nuclear magnetic moment in a magnetic field;in the pulsed case, one applies a sequence of RF pulses called π-pulses (180 degree pulses) orπ/2-pulses (90 degree pulses) and looks for “free induction decay” and “spin echoes”. Below, we give a very simplified introduction, based on classical ideas, to the physics of NMR. More thorough discussions, focusing on the CWNMR technique, may be found in in the booksby Preston and Dietz [1] and Melissinos [2] (see references). In particular, the chapter in Prestonand Dietz gives a nice description of the connection between quantum-mechanical and semiclassical approaches to NMR physics. For a comprehensive treatment of NMR, see the book bySlichter [3].
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Real-Time Magnetic Field Monitoring in Magnetic Resonance Imaging
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Imperfections in the magnetic gradient fields for image encoding can severelydeteriorate the quality of magnetic resonance imaging (MRI), especially in thecase of advanced imaging applications such as fast-acquisition, phase-contrastbased flow quantification, and diffusion-tensor imaging. Gradient field imperfections are caused by eddy currents induced in the conductive structures of theMRI scanner, gradient amplifier nonlinearities, and anisotropic gradient delays,as well as system instabilities and parameter drifts caused by heating. It is expected that by addressing these gradient-encoding disturbances, the diagnosticcapabilities of MRI could be significantly improved for both research and routine clinical applications. In this thesis, different approaches to improving thequality of MRI are investigated using a dedicated magnetic field monitoring system, especially in the context of the advanced imaging applications mentionedaboveThe performance requirements of dedicated magnetic field monitoring systems are derived from general MRI encoding considerations, and the respectivecapabilities of existing magnetometer techniques are explored. Implementationsof the most promising techniques, such as pick-up coils and nuclear magneticresonance (NMR) probes, are further studied in both theory and practice. Theanalysis shows that, of these two approaches, only the nuclear magnetic resonance probes provide a basis for delivering the desired performance necessaryfor improving image quality.
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Rotational resonance of magnetoinductive waves Basic concept and application to nuclear magnetic res
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Metamaterials research seeks to understand how the electromagnetic properties of a material can be changed, by inserting a set of usually identical elements in a random or periodic manner. The topic was popular after the second World War for applications in radar antennas and was further studied in the 1980s and 1990s in the search for chiral materials. A recent stimulus was the reevaluation of three seminal papers on, respectively, negative refractive index material by Veselago,1 the split ring resonator2 also known as slotted tube resonators3 and loop-gap resonators4 , and metallic rod structures5 which offer low plasma frequencies. In 1999 Pendry et al.6 showed that split ring resonators SRRs may produce negative permeability within a certain frequency range near to their resonant frequency. Smith et al.7 then combined SRRs and rods to produce a material with both negative permittivity and permeability. Later they validated Veselago’s prediction of negative refraction.8 Though some reservations have been expressed, negative refraction essentially follows from the existence of backward waves, which have formed the basis of a number of microwave devices.9 In fact, Lindell et al.10 have suggested that negative index media should be called backward wave media.
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Sensitivity Enhancement of NMR Spectroscopy Receiving Chain Used in Condensed Matter Physic
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Assurance of high measuring sensitivity is one of the most challenging issues for any nuclear magnetic resonance (NMR) spectroscopy system. To this end, we propose an accurate noise model of the entire probe-to-spectrometer receiving chain for condensed matter physics, based on the concept of noise figure. The model predicts the propagation of both the signal and noise levels in every component of the NMR spectroscopy receiving chain. Furthermore, it enables identification of the \"weakest\" component and, therefore, the optimization of the whole system. The most important property of the proposed model is the possibility to find system parameters that reduce the measurement time by an a priori calculation, rather than an a posteriori approach. The model was tested experimentally on several different samples. It was found that the measurement time can still be significantly shortened, down to at least one half of the measurement time, starting from optimized conditions with commercially available components. Thus, the proposed model can be used as a tool for both quantitative analysis of the noise properties and a sensitivity prediction of practical NMR systems in physics and material science.
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SENSITIVITY IMPROVEMENT OF A NUCLEAR MAGNETIC RESONANCE METHOD TO MONITOR A BIOARTIFICIAL PANCREAS
标签:NMR核磁共振成像
积分:1 类型:技术书籍上传者:太白金星上传时间:2021-08-31
简介:Non-invasive monitoring of implanted devices is becoming key in developing tissueengineered structures intended to provide alternative or complementary treatment to people with organ or tissue impairment and/or loss. Bioartificial pancreases for the treatment of Type I diabetes are an example of such structures under development. Nuclear magnetic resonance (NMR) imaging and spectroscopy have already shown their potential for monitoring of these pancreatic substitutes and detecting their early marker of failure. However, the sensitivity of these NMR methods was limited. The studies presented in this dissertation investigate sensitivity improvement by developing inductively-coupled implantable RF coil systems at high magnetic field strength not only for 1 H detection, but also for the detection of other informative, but less sensitive nuclei, such as 19F and 31P. An inductively-coupled implantable coil system was first developed for 1 H detection to demonstrate the use on inductively-coupled implantable coil system at 11.1 T. Secondly, a development of a receive-only inductively-coupled implanted coil system was investigated to further improve 1 H detection and increase localized spectroscopy performance. The feasibility of double frequency inductively-coupled implantable coil systems for simultaneous detection of 1 H31P and 1 H19F were explored next, toward the development of a multiple frequency system. The requirements of these coil systems for a complete monitoring of a bioartificial construct were discussed. In parallel to the coil system developments, the inclusion of an RF coil within the implanted pancreatic construct was also studied to address the restrictions it imposed on the construct design. The results for 1 H detection establish that large gains in signal-to-noise can be obtained with the use of inductively-coupled implanted coil systems when compared to the use of standard surface coils. This improvement provides a means to better analyze the structures of implanted bioartificial constructs and their changes over time on NMR images. It can also lower the limit of detection when spectroscopy is performed to detect choline NMR signal and allow for better quantitative analysis of bioartificial organ functions. A receive-only inductively-coupled implanted coil system was also successfully developed to further enhance localized spectroscopy since a more homogeneous NMR excitation magnetic field could be achieved with its use compared to the use of a transmit-receive system. 31P and 19F spectroscopy was also performed using single-frequency inductively-coupled implanted coil system for 31P detection to detect adenosinetriphosphate (ATP) and for 19F detection to detect perfluorocarbons (PFC). These results set the standards for the development of double-frequency inductively-coupled implantable coil systems. The feasibility of doublefrequency inductively-coupled implantable coil system was assessed as well. Furthermore, data shows that a coil-construct assembly allowed insulin-producing cells to function and stay viable for extended periods of time in vitro. The return to normoglycemia in diabetic mice after coilconstruct assembly implantation was also demonstrated while enhanced non-invasive monitoring of the implanted constructs was made possible using NMR methods.
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Signal feedback applications in low-field NMR and MRI
标签:NMR核磁共振成像
积分:1 类型:应用文档上传者:太白金星上传时间:2021-08-31
简介:Tuned pick-up coils with high quality factors Q are used in NMR and MRI for high-sensitivity and low-noise detection. However, large Q-factors introduce bandwidth issues at low frequency and the associated enhanced currents may cause significant radiation damping effects, especially with hyperpolarised samples. Signal feedback can be used to actively control these currents and adjust the detection bandwidth without resistive losses. Capacitive and inductive coupling methods are compared using detailed models and the operating conditions for efficient feedback with negligible noise penalty are discussed. Several high-impedance commercial preamplifiers have been found to affect the resonance characteristics of tuned coils in a gain-dependent way, or could not be used in low-frequency NMR because of oscillations at large positive gain. This is attributed to an undocumented internal feedback, and could be neutralised using external feedback. The implementation of an inductive coupling scheme to feed a suitably amplified phase-adjusted signal back into the PU coils of low-field NMR systems is described, and three experimental applications are reported. One system is used for NMR studies of distant dipolar field effects in highly polarized liquid 3He without or with radiation damping. The moderate intrinsic Q-factor (≈7) could be reduced (down to 1) or increased (up to 100) to control transient maser oscillations. Another system was used for MRI of water samples around 2 mT with Q ≈190 Litz-wire detection coils. The detection bandwidth was increased by actively reducing the Q-factor to obtain uniform sensitivities in images and avoid artifacts introduced by intensity corrections. Finally, parallel acquisition in MRI was performed using two separately tuned detection coils placed above and below the sample. They were actively decoupled using two feedback systems. For an imaging field of view smaller than the sample, artifact-free unfolded images demonstrate the efficiency of this active coil decoupling scheme.
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Simulation and Prototyping of an X-Nuclei MR Coil
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Multi-nuclei imaging (X-nuclei Magnetic Resonance Imaging (MRI)) applications based on different nuclei such as carbon 13C, fluorine 19F, sodium 23Na or phosphor 31P, offers a wide-range of methods for studies of e.g. metabolic processes or non-1H contrast agents. For this purpose, Radio Frequency (RF) coils with their resonance frequency adjusted to the different Larmor frequencies of the corresponding nuclei are required. In this thesis, a new approach of a X-nuclei receive chain (incorporating the RF coil and the Low Noise Amplifier (LNA), respectively) is introduced. Therefore, a new simulation-based Magnetic Resonance (MR) coil design flow is introduced in this thesis as a basis for defining the requirements for the new X-nuclei receive chain. This design flow takes the entire MR imaging process into account and is validated using a manufactured prototype coil, whose Signal to Noise Ratio (SNR) performance was optimized based on the presented design flow, by comparing the coil’s measured performance against the simulated results. Due to safety aspects, custom built coils can not be connected plug and play on a clinical MR system. To get around these limitations, a vendor independent receive-only system, which operates in parallel to an clinical MRI system (host system) is introduced. Comparing the afore mentioned simulation with corresponding measured results, the mean μ and the standard deviation σ of the relative error between the simulated and measured coil sensitivity pattern was found to be μ = 1.79 % and σ = 3.15 %, whereas the deviation between the simulated and measured voxel SNR was found to be less than 4 %. This validates the proposed simulations-based design flow, since the simulations are in good accordance with the measured results.
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Single chip dynamic nuclear polarization microsystem
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:The integration on a single chip of the sensitivity-relevant electronics of nuclear magnetic resonance (NMR) and electronspin resonance (ESR) spectrometers is a promising approach to improve the limit of detection, especially for samplesin the nanoliter and subnanoliter range. Here we demonstrate the co-integration on a single silicon chip of the frontend electronics of an NMR and an ESR detector. The excitation/detection planar spiral microcoils of the NMR andESR detectors are concentric and interrogate the same sample volume. This combination of sensors allows to performdynamic nuclear polarization (DNP) experiments using a single-chip integrated microsystem having an area of about2 mm2. In particular, we report 1H DNP-enhanced NMR experiments on liquid samples having a volume of about 1nL performed at 10.7 GHz(ESR)/16 MHz(NMR). NMR enhancements as large as 50 are achieved on TEMPOL/H2Osolutions at room temperature. The use of state-of-the-art submicrometer integrated circuit technologies should allowthe future extension of the single-chip DNP microsystem approach proposed here up the THz(ESR)/GHz(NMR)region, corresponding the strongest static magnetic fields currently available. Particularly interesting is the possibilityto create arrays of such sensors for parallel DNP-enhanced NMR spectroscopy of nanoliter and subnanoliter samples.
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The Exploration and Application of Nuclear Magnetic Resonance (NMR) An investigation into the compou
标签:NMR核磁共振成像
积分:1 类型:应用文档上传者:太白金星上传时间:2021-08-31
简介:Within the field of physics, there are many ways that one can analyze acompound to better understand its properties and how it functions when interacting withother materials. One of the various methods employed by scientists today is the methodof nuclear magnetic resonance spectroscopy. Before further explaining what NMRspectroscopy is, it is prudent to explain some fundamental facts and propertiesregarding atoms and how the application of a magnetic field can affect said atoms. Allatoms have a nucleus as a center and contained within said nucleus are nucleons. Thesenucleons, which are also referred to as protons or neutrons, have a spin and magneticmoment, which causes them to act in a manner similar to that of small magnets. Withthis established, one may now discuss how the application of a magnetic field and themeasurement of the effect said field has on the substance being analyzed can giveinformation about the material. NMR, or Nuclear Magnetic Resonance, has a long history of study, beginningprimarily in the 1940s through two separate researchers, Felix Bloch and Edward MillsPurcell. Their work led to the moment in 1952, where “the Nobel Prize for physics wasawarded to Felix Bloch and M. Purcell. In his Nobel lecture, 11 December, 1952,entitled ‘Research in nuclear magnetism’ Purcell already described all basic quantitiesand processes controlling NMR spectra” (Pfeifer 155). With the basics of nuclearmagnetic resonance established, later developments went into application. One exampleof this development in application came in the years following Bloch and Purcell as“Organic Chemists soon found that NMR spectroscopy was an ideal technique forelucidating or verifying the structure of moderate sized molecules” (Becker 297)
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The Quantum Origins of the Free Induction Decay Signal and Spin Noise
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Experiments are described that elucidate the quantum mechanical origins of the free induction decay voltage and of spin noise. It is shown that the experimentally measured FID voltage induced in a Hertzian loop receiving coil following a 90° pulse is typically two orders of magnitude too large to be accounted for by the current quantum theory of signal reception—coherent spontaneous emission. An experiment is then presented in which spin noise is easily observed in a circuit with a Q-factor of order unity, thereby undermining a popular hypothesis that such noise is due to spontaneous emission and is only observable because of the enhancement in the density of the radiation field in a high Q-factor tuned circuit, the NMR probe. Both the free induction decay and the spin noise are shown to be accurately predicted by near-field Faraday induction, which is described in the theory of quantum electrodynamics by an exchange of virtual photons. A heuristic approach to understanding the nature and role of virtual photons in the signal reception process is then given. Thus current popular statements that observation of the magnetic resonance phenomenon relies on the absorption and emission of radio waves are shown to be wrong
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TOWARDS CMOS NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY DESIGN, IMPLEMENTATION AND EXPERIMENTAL RESULTS
标签:NMR核磁共振成像
积分:1 类型:应用文档上传者:太白金星上传时间:2021-08-31
简介:Nuclear Magnetic Resonance (NMR) Spectroscopy is used intensively along with otherancillary spectroscopic and characterization techniques. The design and implementation ofHigh Throughput NMR Spectroscopy is a key challenge to accelerate the drug discoveryprocess. On the other hand, the current conventional NMR technologies are expensive andbulky. The development of novel handheld NMR spectroscopy is a key challenge towardsNMR spectroscopy for Point-of-Care (PoC) diagnostics applications. This thesis addresses the above-mentioned challenges of High Throughput NMRSpectroscopy and Handheld NMR spectroscopy by developing new integrated circuitsdedicated to NMR spectroscopy using Complementary Metal Oxide Semiconductor(CMOS) technology. Simulation and characterization results were also used to prove thefunctionality and applicability of the proposed techniques. We have designed two CMOSchips using 0.13-μm technology, first chip includes number of new vertical microcoils andLNA with 780 pV/√Hz at 300 MHz and the second one is a new dual-path NMR receiver.
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Triple resonant electromagnetic structures for polarization transfer in DNP
标签:NMR核磁共振成像
积分:1 类型:学术论文上传者:太白金星上传时间:2021-08-31
简介:Despite, its low inert sensitivity, it is irrefutable that nuclear magnetic resonance (NMR) isextremely useful for both analytical spectroscopy and imaging. As the study of magneticresonance evolved, detection instruments improved and magnets increased yielding modestimprovements to sensitivity. Ultimately, it is the polarization of nuclear spins betweenZeeman energy levels that dictate the NMR signal intensity. Several hyperpolarization methods exist in aiding to increase nuclear spin polarizationbut it is dynamic nuclear polarization (DNP) the offers the most versatility in application toan exhaustive range of nuclear spins. The method relies on transferring spin polarizationfrom unpaired electrons to nuclear spins facilitated my irradiation at the electron resonantfrequency. In 2003, a technique emerged based on DNP to produce polarized liquid-state solutions. The technique involves cooling a sample to approx. 1 K in a high magnetic field (≥ 3.35T) where electron spin polarization is very high and rapidly dissolving the sample with ahot solvent to produce the solution. Dissolution dynamic nuclear polarization enabled realtime surveillance of metabolic conversions in both spectral and spatial dimensions, findingemployment in the study of cancer progression and response to therapy. Polarizer systems have since rapidly evolved to primarily reach higher nuclear polarization levels, but also increase sample throughput, limit dependence on cryogenics andincorporate automation. The latest polarizer design realizes a variable field (up to 10.1T) cryogen-free polarizer system. This thesis serves to investigate the development of instruments to improve the polarization process in a system of that type. Herein a probe isdeveloped facilitating the ability to perform double resonance solid-state DNP experimentswith dissolution capabilities. Moreover, the design is optimized to minimize static heat load,manufacturing complexity and cost. To improve throughput another probe capable of performing cross-polarization is developed, yielding 27% 13C polarization with a 12 min build-up time that is twice the direct13C polarization and 4.4 times faster. Dissolution compatible coil geometries are explored. Techniques to design single and double resonant detection circuits including methods toevaluate their sensitivity is discussed. In low pressure environments arcing is probable dueto high voltages during pulsing. As such, arc detection methods and mitigation strategiesare explored and experimentally verified.

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