Concepts in magnetic resonance最新文献

{"title":"Suppression of linearly responsive residual water","authors":"Shanmin Zhang, Xianbin Yang, D. Gorenstein","doi":"10.1002/CMR.10003.ABS","DOIUrl":"https://doi.org/10.1002/CMR.10003.ABS","url":null,"abstract":"The residual water, coming from a region away from the center of the RF coil and therefore experiencing a much smaller flip-angle than the designed one, may not be well suppressed in certain water-suppression experiments. To suppress the residual water efficiently, a composite 90°x90°y90°-x90°-y pulse is used in the WET sequence, which de-excites molecules experiencing small flip-angles. The composite pulse, however, has two null excitation points near on-resonance, causing a severe loss of spectrum intensity and baseline distortion toward the null points. A phase inversion at each null point is found in the excitation profile of the composite pulse. This phenomenon is explored in detail. Because the residual water experiences a very small flip-angle, it can be treated as a linear spin system, i.e., its peak intensity is proportional to the flip-angle. Based on this principle, the residual water can be reduced dramatically by replacing the 90° pulse in the WET sequence with a 270° pulse for one out of every four scans. Unlike the composite pulse, this scheme does not introduce noticeable loss of spectrum intensity and baseline distortion.","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"14 1","pages":"102-111"},"PeriodicalIF":0.0,"publicationDate":"2002-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51498333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Receiver imperfections and CYCLOPS: an alternative description","authors":"D. Reichert, G. Hempel","doi":"10.1002/CMR.10004.ABS","DOIUrl":"https://doi.org/10.1002/CMR.10004.ABS","url":null,"abstract":"We present a quantitative approach to describe the spectral artifacts that are introduced into the NMR spectrum by imperfections of the receiver electronics of the NMR spectrometer (\"mirror image\" or \"ghost\", \"transmitter spike\"). In contrast to the commonly used graphical representation, it is based on a rigorous algebraic treatment and provides quantitative results on the intensities and phases of the artifacts easily. We apply this approach to the quantitative explanation of the well-known Cyclically Ordered Phase Sequence phase cycle (CYCLOPS) that serves to suppress the receiver imperfections and thus to remove the artifacts from the frequency spectrum. Finally, we compare the algebraic results with a graphical approach and demonstrate that the application of CYCLOPS minimizes the artifacts even if the spectrometer has deficiencies in the transmitter electronics.","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"14 1","pages":"130-139"},"PeriodicalIF":0.0,"publicationDate":"2002-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51498343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Solutions and linearization of the nonlinear dynamics of radiation damping","authors":"D. Rourke","doi":"10.1002/CMR.10005.ABS","DOIUrl":"https://doi.org/10.1002/CMR.10005.ABS","url":null,"abstract":"The techniques of Painleve analysis and Lie algebra analysis were applied to the nonlinear Bloch equations with radiation damping. Painleve analysis is useful in finding when explicit solutions exist to a nonlinear system. It was applied to the radiation-damped system with damping time Tr, and with T1 and T2 relaxation, but with no externally applied radiofrequency (RF) pulse. Two cases were identified where explicit solutions could be found. The first case ( 1/T1:0) is well known, the second case ( 1/T1=1/Tγ+1/T2) is apparently not previously known. Lie algebra analysis was used to show that the system with no relaxation, but with an externally applied RF pulse, could be transformed into a linear system. This simplifies the forward problem of finding the magnetization response to a given pulse. It also allows the inverse problem to be solved, where the pulse is calculated to result in a given magnetization response as functions of both resonance offset and radiation damping time.","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"14 1","pages":"112-129"},"PeriodicalIF":0.0,"publicationDate":"2002-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51497963","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Adiabatic radiofrequency pulse forms in biomedical nuclear magnetic resonance","authors":"D. Norris","doi":"10.1002/CMR.10007.ABS","DOIUrl":"https://doi.org/10.1002/CMR.10007.ABS","url":null,"abstract":"Adiabatic radio frequency (RF) pulses are in widespread use in biomedical magnetic resonance imaging and spectroscopy. The primary advantage of adiabatic pulses is that provided the condition for adiabatcity is satisfied they can be made insensitive to inhomogeneities in the RF field. In this pedagogical article the principles of adiabatic fast passage (AFP) are explained, and the use of AFP to invert both stationary and flowing spin systems is examined. The hyperbolic secant pulse is presented as a pulse capable of performing slice selective adiabatic inversion. Lower power alternatives to this pulse are described, and the principle of offset independent constant adiabaticity is elucidated. Instantaneous reversal of the orientation of the effective RF field as a means of producing excitation and refocusing pulses is presented, as are methods of obtaining slice selective excitation with these pulses.","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"1 1","pages":"89-101"},"PeriodicalIF":0.0,"publicationDate":"2002-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51498080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An introduction to hydrogen bond scalar couplings","authors":"A. Dingley, F. Cordier, S. Grzesiek","doi":"10.1002/1099-0534(2001)13:2<103::AID-CMR1001>3.3.CO;2-D","DOIUrl":"https://doi.org/10.1002/1099-0534(2001)13:2<103::AID-CMR1001>3.3.CO;2-D","url":null,"abstract":"The hydrogen bond (H-bond) has been recognized in science for more than 80 years as a concept to explain situations where a hydrogen atom is simultaneously binding to two other atoms. Due to the moderate energies necessary for their formation and rupture, hydrogen bonds play a fundamental role in many chemical reactions and most, if not all, interactions involving biological macromolecules. For both proteins and nucleic acids, H-bonds are the essential element in the formation of secondary structures and often they also participate in the stabilization of tertiary structures. Many properties of H-bonds have been studied by a large variety of experimental methods, including NMR spectroscopy. Recently, electron-mediated scalar couplings have been observed which connect magnetic nuclei on both sides of the hydrogen bridge. In contrast to earlier NMR observables, these couplings can be used to \"see\" all partners of the hydrogen bond, the donor, the proton, and the acceptor in a single COSY experiment. In addition, the size of the coupling constant can be related to hydrogen bond distances and angles. This article should serve as an introduction to these findings and illustrate their use by various examples. (C) 2001 John Wiley & Sons, Inc.","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"6 3","pages":"103-127"},"PeriodicalIF":0.0,"publicationDate":"2001-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50803804","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The relationship between ensemble quantum computing logical gates and NMR pulse sequence engineering exemplified by the SWAP operation","authors":"T. Schulte-Herbrüggen, O. W. Sørensen","doi":"10.1002/1099-0534(2000)12:6<389::AID-CMR2>3.3.CO;2-K","DOIUrl":"https://doi.org/10.1002/1099-0534(2000)12:6<389::AID-CMR2>3.3.CO;2-K","url":null,"abstract":"","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"7 4","pages":"389-395"},"PeriodicalIF":0.0,"publicationDate":"2000-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50804004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Biological effects and health implications in magnetic resonance imaging","authors":"A. Kangarlu, P. Robitaille","doi":"10.1002/1099-0534(2000)12:5<321::AID-CMR4>3.3.CO;2-A","DOIUrl":"https://doi.org/10.1002/1099-0534(2000)12:5<321::AID-CMR4>3.3.CO;2-A","url":null,"abstract":"In this work, the safety aspects of the Magnetic Resonance Imaging and Spectroscopy (MRI/MRS) systems are reviewed. Focus is placed on the interaction between the electric and magnetic fields generated by such instruments and the human body. An understanding of these interactions has become ever more important with the push to higher field strengths. Knowledge of MRI safety can not only guide RF coil and pulse sequence design but can also affect sequence selections, thereby ensuring safe and efficient system operation. Due to the signal to noise advantages of high field MRI systems, increases in the static magnetic field are inevitable. However, in addition to the static magnetic field, power intense sequences, fast gradient switching, and localized imaging/spectroscopy all have the potential of subjecting the human body to intense magnetic and electric field fluctuations. This further accentuates the need for a detailed understanding of the effects of exposure to these fields. In this work, some of the issues addressed are new, while others are well established. In either case, it is hoped that this compilation will enable all of us to pay greater attention to these matters and increase the current state of understanding through novel experimental studies. The discussion broadens the range of radio frequency effects to the microwave limit. This was accomplished in view of the latest efforts for realization of ultra high field (UHF) human MRI. In this regard, recently constructed ultra high field whole body systems will provide a new testing ground for safety issues. The proliferation of high field (1.0–3.0 tesla), very high field (3.0–7.0 tesla), and ultra high field (≥7 tesla) whole body MRI's calls for a review of the safety literature that can guide future studies of critical health related issues. An effort has been made to present an up to date analysis of the biological effects within MR, covering a wide range of properties from cellular and physiological to clinical. © 2000 John Wiley & Sons, Inc. Concepts Magn Reson 12: 321–359, 2000","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"19 8","pages":"321-359"},"PeriodicalIF":0.0,"publicationDate":"2000-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50803864","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Solid-state NMR imaging methods. part I: strong field gradients","authors":"D. Demco, B. Blümich","doi":"10.1002/1099-0534(2000)12:4<188::AID-CMR2>3.3.CO;2-Z","DOIUrl":"https://doi.org/10.1002/1099-0534(2000)12:4<188::AID-CMR2>3.3.CO;2-Z","url":null,"abstract":"NMR imaging has been shown to be a viable and useful approach to exploring spatial chemistry and molecular dynamics of a wide range of materials. NMR provides image contrast which is fundamentally different from that of other methods. The principles of NMR imaging and spatial information applicable to materials are reviewed, and examples of current development are given. Of fundamental importance for spatial resolution in solid-state imaging are the relationships between NMR linewidth, image resolution, signal-to-noise ratio, and measuring times. The principles of NMR with spatial resolution by frequency and phase encoding are introduced. The NMR line-broadening effect characteristic for dipolar and quadrupolar solids or quasisolids can be surpassed by strong field gradients or line-narrowing methods. Correspondingly, one class of NMR imaging methods uses stray fields, strong oscillatory gradients, or multiple-quantum coherences evolution. It is discussed in Part I. In Part II the basic principles of the second class using line-narrowing methods by magic-echoes, magic-angle sample spinning, multiple-pulse excitation, and magic-angle rotating frame techniques are presented. The possibility of recording spatially resolved spectroscopic parameters by these methods is also addressed. © 2000 John Wiley & Sons, Inc. Concepts Magn Reson 12: 188–206, 2000","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"22 1","pages":"188-206"},"PeriodicalIF":0.0,"publicationDate":"2000-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50803789","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimum window function for sensitivity enhancement of NMR signal","authors":"D. Traficante, Masoumeh Rajabzadeh","doi":"10.1002/(SICI)1099-0534(2000)12:2<83::AID-CMR3>3.3.CO;2-8","DOIUrl":"https://doi.org/10.1002/(SICI)1099-0534(2000)12:2<83::AID-CMR3>3.3.CO;2-8","url":null,"abstract":"","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"285 6","pages":"83-101"},"PeriodicalIF":0.0,"publicationDate":"2000-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50683202","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Protein structure in anisotropic environments: Unique structural fold from orientational constraints","authors":"J. Quine, T. Cross","doi":"10.1002/(SICI)1099-0534(2000)12:2<71::AID-CMR2>3.3.CO;2-I","DOIUrl":"https://doi.org/10.1002/(SICI)1099-0534(2000)12:2<71::AID-CMR2>3.3.CO;2-I","url":null,"abstract":"The mathematical foundation of the determination of protein structure from orientational constraints is described. The tools used are vector algebra, gram matrices, and determinants. The discussion begins in the general abstract setting and proceeds to a discus- sion of how the methods can be applied to the determination of protein structure using solid state nuclear magnetic resonance. Examples are given relating to the structure of the peptide gramicidin A. © 2000 John Wiley & Sons, Inc. Concepts Magn Reson 12: 71-82, 2000.","PeriodicalId":89665,"journal":{"name":"Concepts in magnetic resonance","volume":"60 4","pages":"71-82"},"PeriodicalIF":0.0,"publicationDate":"2000-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50682772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}