tag:blogger.com,1999:blog-3300702123878659843.post4645654691936519293..comments2024-03-26T05:25:50.831-04:00Comments on University of Ottawa NMR Facility Blog: Echoes, T2 Measurements and DiffusionGlenn Faceyhttp://www.blogger.com/profile/05146575170575279335noreply@blogger.comBlogger12125tag:blogger.com,1999:blog-3300702123878659843.post-54975850576834416102023-10-17T13:44:03.298-04:002023-10-17T13:44:03.298-04:00Riley L.
I’m not sure I can provide an answer. I ...Riley L.<br />I’m not sure I can provide an answer. I have never seen a T2 measured where the total CPMG time was held constant with both tau and the number of loops varied. <br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-21137189640466167522023-10-17T13:15:42.229-04:002023-10-17T13:15:42.229-04:00Hello, I've been seeing two different methods ...Hello, I've been seeing two different methods for conducting T2 measurements with the CPMG pulse sequence. One described here where you choose a constant tau and vary the number of loops and the other where the total CPMG time is held constant and the tau and number of loops are changed. I'm curious if one method is better or there is a reason for one over the other? Riley L.https://www.blogger.com/profile/04709615846538993443noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-80507909909483591552019-05-27T12:23:32.163-04:002019-05-27T12:23:32.163-04:00Unknown,
The pulse sequence certainly doesn't ...Unknown,<br />The pulse sequence certainly doesn't prevent molecular motion. The losses due to diffusion are experienced during the tau delay periods. The diffusion losses are not additive from one tau period to another. Diffusion losses are thus reduced by using an echo train with short tau delays rather than repeated mesurements as a function of tau (with long tau).<br /><br />Glenn Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-20553928096744039152019-05-26T07:06:04.256-04:002019-05-26T07:06:04.256-04:00Hello,
Can you please expand on how using en echo-...Hello,<br />Can you please expand on how using en echo-train dismisses the effect of diffusion.<br />After all, even in the echo train sequence the molecules are still moving through the sample, so why won't we see the same signal loss X milliseconds into the echo-train as at a Hahn-echo with \tau=x milliseconds?<br />Are the consecutive 180 pulses somehow preventing the molecules from moving too far?Anonymoushttps://www.blogger.com/profile/15656560906981832231noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-79745310079835621102018-04-26T10:46:07.857-04:002018-04-26T10:46:07.857-04:00Ram,
One should choose values of tau which are at ...Ram,<br />One should choose values of tau which are at least 10 times the duration of the 180 deg pulse and short enough such that the diffusion during tau is not significant. For macromolecules tau can be quite large (hundreds of msec to seconds). For small molecules tau should be chosen msec to tens of msec.<br /><br />The only way I know to cross check the T2 is through a literature search. The measured T2 via CPMG must always be equal to or longer than that measured from the line width of the resonance (1/(pi*(width at half height))). It will also always be shorter than the T1.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-27370152819303593052018-04-25T08:23:44.446-04:002018-04-25T08:23:44.446-04:00Hi Glen,
What is the reasonable 'Tau' val...Hi Glen,<br /><br />What is the reasonable 'Tau' value (which is constant) between a 90deg and the 180deg pulse in case of CPMG echo train sequence for T2 measurements? I just need the minimum and maximum values of it for different samples if possible. Also, how to cross-check whether the measured T2 value for a certain sample is right or wrong? Thank you so much in advance.<br /><br />best wishes,<br />RamAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-3347761560635752502016-04-29T14:44:03.144-04:002016-04-29T14:44:03.144-04:00Emilia,
It is best to use the sequence with the CP...Emilia,<br />It is best to use the sequence with the CPMG echo train.<br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-33628156542519015162016-04-28T17:51:25.343-04:002016-04-28T17:51:25.343-04:00I Glenn,
Which sequence gives the more accurate va...I Glenn,<br />Which sequence gives the more accurate value of T2 to satisfy the relation with the line width?D=1/(pi*T2).<br />Thanks a lotAnonymoushttps://www.blogger.com/profile/15573340924331032646noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-4271442543203158282016-03-08T09:27:10.353-05:002016-03-08T09:27:10.353-05:00Ambrish,
I really do not know the answer to your q...Ambrish,<br />I really do not know the answer to your question. My feeling is that the CPMG method should work fine provided you use the integrals for analysis rather than signal height. You can confirm this by repeating your measurement in using a probe with a much lower Q where radiation damping is not an issue.<br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-2410271042028119312016-03-08T03:48:50.207-05:002016-03-08T03:48:50.207-05:00Hi Glenn,
Can T2 of water proton in 90%H2O+10%D2O...Hi Glenn,<br /><br />Can T2 of water proton in 90%H2O+10%D2O sample be calculated using Bruker standard CPMG pulse?<br />Will radiation dumping affect T2 relaxation of water proton? What pulse program should I use for T2 calculation of water proton in 90%H2O+10%D2O.<br /><br />Thanks<br /><br />Ambrishambrishhttps://www.blogger.com/profile/15339661927099084579noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-81085980759825269462015-04-10T08:17:05.725-04:002015-04-10T08:17:05.725-04:00Hi Julian,
Thank you for the question. The answe...Hi Julian,<br /><br />Thank you for the question. The answer is Yes.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-47542551468961595682015-04-10T06:49:17.526-04:002015-04-10T06:49:17.526-04:00Can T2 be calculated from the signal intensity of ...Can T2 be calculated from the signal intensity of each FID recorded for each echo of the last pulse sequence in your CPMG figure?<br /><br />Thanks<br />JulianJulian Haighhttps://www.blogger.com/profile/13189790510964997695noreply@blogger.com