Talk:Relaxation (NMR)

Adding section header

I have a serious problem with this page. NMR relaxation is a very broad phenomena (and very complicated), which has very different characteristics depending on the exact physical conditions where it occurs. I feel this page consideres only one specific case. For instance T2 (in contrast to T1) is much MORE dependant on the magnetic field in solution NMR on large molecules and in the case of small molecules they are nearely the same. NMR relaxation is an important issue in all applications of NMR (not just MRI). I think this page gives a very misleading picture of NMR relaxation, without explainig what NMR relaxation is. I would like to correct this page but, I know very little about NMR relaxation in the solid state or about the use of the concept in MR Imaging, so I would be gratefull for some feedback. -- Flogiston

• You forgot to sign your name. :) I am currently a student with a major in MRI, and still know very little about the whole picture of it, not to mention NMR in a standard chemistry sense. What I put on is to summarize some info about the relaxation I've learned these 2 plus years, since there were no more detailed info about this in Wikipedia as far as I knew. This page is not complete in my opinion. You can still make this page better by sharing your knowledge about it. --KasugaHuang 06:55, 5 December 2006 (UTC)

As someone who has spent a lot of his life doing NMR I can only agree that this article needs a lot of expansion. Unfortunately I don't have the time to do it. Topics that should be added would be Relaxation Mechanisms, Relaxation in organic vs inorganic systems, Molecular motions and their relationship to relaxation, Measurement of T1 and T2, Quadrupolar effects, Anisotropic media and many others. nmrtian

There should also be a section on T1 rho, spin-lattice relaxation in the rotating frame. -- jpdemers

is it just me or should the longitudinal relaxation refer to the component of M that is pointing PARALLEL to B0 instead of perpendicular? -dc

Section on why T1>T2>T2*

This section doesn't make any sense. Well, I guess it sort of makes sense, it doesn't actually say anything about why T1>T2>T2*.Fantumphool (talk) 15:17, 15 August 2008 (UTC)

I am not an expert on this in any way, but I do know a bit, and I've read this claim with similar vague explainations. It seems to me that this statement is being too confident in the model applied. I personally think the following makes a lot more sense, but am hesitant to put it in without someone backing me up:

"The following always holds true: T1 > T2 > T2*. This is because, if the perpendicular magnetisation decays more slowly than the z-component (ie. T2 > T1) then the components of the magnetisation vector would violate the Heisenberg uncertainty principle. This means that for systems where spin-spin relaxation has a greater effect than spin-lattice relaxation, a different model is needed, and so the labels T1 and T2 as used in this article do not apply."

This makes, to me, a lot more sense, but it is based mostly on intuition. Piemonkey (talk) 18:14, 27 October 2008 (UTC)

Those explanations ("not dephased by the time the sample had returned to equilibrium" and "would violate the Heisenberg uncertainty principle") do not seem to have a sound foundation. Mathematically, the phenomenological Bloch equations allow for T2 > T1. However, the reason T2 < T1 must come from the physical origin of relaxation. T1 represents the rate at which a spin comes into thermal equilibrium with the lattice. T2 represents the rate at which many spins reach thermal equilibrium amongst themselves. This happens, in a time much shorter than T1, since various forms of spin-spin couplings make rapid energy transfer possible. I am not yet sure if we can make a generalized statement about T1 > T2, a citation would be needed to support that statement. —Preceding unsigned comment added by 134.76.223.1 (talk) 22:23, 15 July 2009 (UTC)

From "High-resolution NMR techniques in organic chemistry; By Timothy D. W. Claridge"[1], T2 can never be greater than T1; however, additional mechanisms can operate to reduce T2. 134.76.223.1 (talk) 14:40, 9 July 2010 (UTC)

Comment

This was posted in the middle of the introductory section by 86.140.114.210:

it depends what kind of relaxation we have (if we observe orientation related proceses, then this explanation is correct, if not then it is not correct). In fact, most of spectroscopic technics are based on absorbtion of EM energy by matter (in most cases electron), and in this sense we have no orientation efects, but only changes in number of resonating particles. A fully relaxed state or equilibrium means that all free for that system absorbtion sites are able to bring their own contribution to the resonanse. The opposite notion is saturation, that means no more active (at that time moment) absorbtion sites. Resonance means that at the same time moment (or some very short time which does not affect significantly the spectrum, it has constant contribution) we have absorbtion in volume. This short time interval and sample volume (more precisely the thickness) contribute in the line broadening and are neglected in analysis. In fact, spins are oriented by the external magnetic field in order to obtain the resonance (in other words to get the organised simultaneous absorption). The described above event could take place only then after reaching equilibrium with the applied magnetic field, we sudenly switch it off and look in the temperature dependent spin depolarisation effect. In the sence of magnetic resonance, the relaxation simply means how fast reacting centers release the absorbed EM radiation (and it means that they are able to participate in the resonance again).

It isn't encyclopedic, which is why I moved it here, but I have no idea how correct or otherwise it is. Sectori (talk) 11:52, 8 January 2008 (UTC)

What is the dominant mode of relaxation in solid?

Thanks. —Preceding unsigned comment added by 139.140.100.32 (talk) 15:11, 6 June 2009 (UTC)

Dipole-dipole couplings —Preceding unsigned comment added by 134.76.223.1 (talk) 19:31, 15 July 2009 (UTC)

Relaxation Times and Relationship to correlation times & BPP theory

Hello In solids, relaxation is made by dipolar coupling, Quadrupolar nuclei interaction with electric fields, and chemical shift anisotropy. Please give some calculation details for the BPP theory. First, with 1.5 T and tau = 5e-12 I found w0.tau = 3.19-4 instead of 3.19-5. But, because the K factor is so high, this had not any consequences on the T1 found of 3.92 s (reported article T1 for water were 2200-2400 ms) ; this is the half of the value found. The worse thing in this section is the calculation of K .What are the values used to found K = 1.02×1010 s-2 ? Do you have used µ0=4 pi e-7 ? And for r^6 , the value of r is greatly important. This part of the article is of great importance for fondamental comprehension of the relaxation times.

I have background and publications in NMR relaxation, I will seek to update this page in the next few days or weeks. —Preceding unsigned comment added by Markf science (talk • contribs) 16:59, 8 March 2010 (UTC)

It does not make me sense that in dexoygenated blood T2 is longer than in oxygenated blood: oxygen is a paramagnetic species and should make T2 shorter, not longer. — Preceding unsigned comment added by 147.162.53.202 (talk) 14:41, 24 June 2015 (UTC)

OK: it is correct, since oxygenated haemoglobin is diamagnetic, while deoxygenated haemoglobin is paramagnetic. Sorry for that... — Preceding unsigned comment added by 147.162.53.202 (talk) 16:02, 24 June 2015 (UTC)

R7e6n5s (talk) 20:39, 4 March 2010 (UTC)R7e6n5s Thank —Preceding unsigned comment added by R7e6n5s (talk • contribs) 14:19, 4 March 2010 (UTC)

This section still sucks. Can someone put in a "non extreme case" where you actually get reasonable T1 and T2 times that aren't equal to K? 128.196.56.50 (talk) 21:23, 13 December 2013 (UTC)

Common relaxation times - graph?

The table of common relaxation times in human tissue might be more informative if someone created a graph plotting the different tissues on a scale of T1 and T2. I don't have the tools to do this properly myself but created a rough example. The axes are logarithmic because of the large range of values. human tissues plotted on the plane of T1 and T2 relaxation times

Perhaps the axes could even include common correlates of the values, like "increasing water content". — Preceding unsigned comment added by 24.158.55.115 (talk) 21:44, 20 September 2015 (UTC)

Was there a colour code/key for your png ? - Rod57 (talk) 17:50, 12 January 2018 (UTC)

No mention of Proton Density weighting

Since this article mentions T₁ and T₂ - should it not also mention PD weighting (as in Proton Density, NMR signal and MRI contrast) ? or is that specific to its use in medical MRI ? - Rod57 (talk) 17:56, 12 January 2018 (UTC)