High-Field NMR vs Low-Field NMR

Generally, high-field NMR means the magnet field is higher than 1 Tesla, middle-field NMR means the magnet field is between 1 Tesla and 0.5Tesla, low-field NMR means the magnet field is lower than 0.5T. They have different application fields.Low-field NMR is used for analyzing the reaction among molecules. For example, water can be divided into combine water, free water according to water molecule’s phase, cross-link density of polymer. And high-field NMR is used for molecule structure analysis.

High-Field NMR
->1T (Imaging quality)
-superconducting magnet (Homogeneity)
-Heavy, expensive, higher maintenance cost
Low-Field NMR
-<1T (Less effect by ferromagnetic material )
-permanent magnet (no maintenance cost)
-Low weight, portable, inexpensive

Low-Field NMR analyzer is more suitable for porous media analysis

high-field-nmr-vs-low-field-nmr

Advertisements

Why Only Two Relaxation Times

The relaxation times T1 and T2 were described phenomenologically by Felix Bloch at al representing changes in the net magnetization (M) after RF-stimulation. T1 reflects changes along the direction (z-) of the main magnetic field; T2 reflects transverse (xy-) behavior. There are only two relaxation times because the directions “longitudinal” and “transverse” seem to encompass the cardinal directions in three-dimensional space. The transverse (x- and y-) directions are generally arbitrary and indistinguishable so only a single T2 value is usually applied.

However, some tissues and materials have T2 anisotropy, meaning their observed T2 values differ depending on orientation, so I suppose you could say there are more than one transverse relaxation time for these substances, but they are still called T2’s.

Additionally, in the rotating frame another type of relaxation time is frequency distinguished, T1ρ (“T1-rho”). This relaxation time is somewhat of a hybrid between T1 and T2 that can be measured in when a spin-locking pulse is applied to a system. See our paper from 1996 for further explanation:

Ulmer JL, Mathews VP, Hamilton CA, Elster AD, Moran PR. Magnetization transfer or spin-lock? An investigation of off-resonance saturation pulse imaging with varying frequency offsets. AJNR Am J Neuroradiol 1996.

I have never heard of the “duality” explanation above; it is not correct at all and should be abandoned/discouraged.

PQ001 MRI Contrast Agent Analyzer

Product Description:
The PQ001 NMR Analyzer was launched in 2008. After years of upgrading, PQ001 has many advantages such as small size, high precision, good repeatability, good stability and excellent cost/benefit performance. Based on these advantages, PQ001 has been widely used in MRI Contrast Agent Researches.

Basic Parameters:
  • Magnet: permanent magnet
  • Magnetic field intensity:0.5±0.08T
  • Probe: Ø15mm
  • Size (L x W x H): 1685mm×520mm×386mm
  • Weight: 134Kg

 Functions:
  • Relaxation analysis of T2*,T2 and T1

t1-t2-1

Jeffrey H Simpson NMR Case Studies

NMR Case Studies: Data Analysis of Complicated Molecules provides a detailed discussion of the full logical flow associated with assigning the NMR spectra of complex molecules while helping readers further develop their NMR spectral assignment skills.

The robust case studies present the logic of each assignment from beginning to end, and fully explore the available range of potential solutions. Readers will gain a better appreciation of various approaches and will develop an intuitive sense for when this particular concept should be implemented. This enhances the skill sets of readers by providing a host of methodologies potentially amenable to yielding correct assignments.

Readers will gain a better appreciation of various approaches and will develop an intuitive sense for when this particular concept should be implemented. This enhances the skill sets of readers by providing a host of methodologies potentially amenable to yielding correct assignments. Authored by a scientist with more than 20 years of experience in research and instruction, this book is the ideal reference for anyone in search of application-based content that addresses complicated molecules including corticosteroids, biomolecules, polypeptides, and secondary metabolites.

Features the nuclear magnetic resonance NMR system for EDU spectra of a number of large and interesting molecules, ranging from corticosteroids to secondary metabolites to large synthetically prepared molecules
Uses case studies to pair the spectral signals from the various sites of each molecule to their molecular counterparts in a process called assignment
Includes complex NMR system for research problems, aiding readers in the development of NMR spectral assignment skills
Features input from a leading scientist with over 20 years of research and instruction experience in the field

Authored by a scientist with more than 20 years of experience in research and instruction, this book is the ideal reference for anyone in search of application-based content that addresses complicated molecules including corticosteroids, biomolecules, polypeptides, and secondary metabolites.

Spin Dynamics: Basics of Nuclear Magnetic Resonance

For those studying biomolecules with NMR, the unofficial bible is of course the maroon colored Cavanagh book. Though this is an excellent book, it isn’t the best suited book for beginners. This is where Levitt’s book comes in: this is by far the kindest introduction to NMR that I have seen, with heavy emphasis on understanding the concepts first and the formalism later. The book is full of useful diagrams, detailed analogies, and exercises for the reader where other books only show equations. So borrows someone’s Cavanagh first, and if you get stuck after 20 pages then order yourself a copy of Levitt and you won’t be disappointed. If you already have studied NMR and are looking at how to apply it to proteins, then Cavanagh should suit you fine.

This book could simply be stated as an excellent attempt to introduce the foundations of bench-top NMR. It is a very good primer on all theoretical aspects that are essential to an understanding of the subject.
It offers a methodical, step-by-step approach. Useful tools and consistent terminology are the most attracting feature of this volume. It is well-illustrated; and controversial issues are highlighted in the “Notes” sections at the end of each chapter. It has illustrative problems at the end of each chapter, with solutions provided at the end.
Interestingly, the appendix covers many important aspects that are needed at a more advanced stage. Useful tools for the understanding of NMR are developed at appropriate stages. These include: the box notation for coherences, populations, density matrices and transitions; the origin of NMR spectra from individual coherence terms in the density matrix; origin of 2-D NMR signals as well as many important concepts in Fourier Transform NMR are described. The origins of relaxation enjoy a very readable and simplistic approach in the last chapter.
Whenever simplistic approximations are used, the author never claims of completeness or rigour. Distinction is made between terms that are physically correct and terms that are sometimes misleading, but enjoy widespread use in the NMR spectroscopy convention. The essential tools in quantum mechanics are outlined, product operator descriptions are used frequently and repetitively, that enhances understanding and provides more practice. Pictorial representations have been given where possible, a view-point beginners like myself find very useful.
One drawback, is a careful side-lining of the very important technique of using pulse-field gradients, although their cousin technique, named pulse-cycles is quite elaborately explained. I hope, the next issue of the book would also cover up this important technique.