relationship between molecular tumbling rate and T2 relaxation time

[zoey]

the image is here

who can explain the relationship between molecular tumbling rate and T2 relaxation time. Why it is the relationship like this as the image said above.

PS:The movement, or tumbling is rotation, vibration and translation of the molecule in which the hydrogen proton resides. Water molecules, which are the source of most of the signal in MRI, can be found in three states which affect their movement or tumbling.

[aelster]

I think the answer to your question is pretty completely explained on the following Q&A on my site:

http://mriquestions.com/dipole-dipole-interactions.html

If you need more, click on the "Advanced Discussion" tab and you will be taken to a secret hidden page (!) that will fill in even more details.

By the way, the image you chose from the revise MRI site is incorrect. There should be a dip, not a bump in the T2 curve near the Larmor frequency. Use the correct graph from my site instead.

[Allan]

Sorry to post in such an old thread, but I'm also a little confused about T2 dependence on "molecular tumbling" / "correlation time".

I liked the explanation of die T2 dip regarding molecular tumbling here:
https://mri-q.com/why-is-t1--t2.html

However, while browsing through the site I discovered this page:
http://mriquestions.com/bo-effect-on-t1--t2.html
with a bump near Larmor frequency.
Is this an error?

Trying to clear things up, I checked the reference (Bloembergen et.al. 1947). Adding to my confusion, Figure 14 shows a saddle, but not really a dip near Larmor frequency for T2.

thanks and best wishes,
Allan

[aelster]

(11-08-2018 08:37 PM)Allan Wrote:  Sorry to post in such an old thread, but I'm also a little confused about T2 dependence on "molecular tumbling" / "correlation time".

I liked the explanation of die T2 dip regarding molecular tumbling here:
https://mri-q.com/why-is-t1--t2.html

However, while browsing through the site I discovered this page:
http://mriquestions.com/bo-effect-on-t1--t2.html
with a bump near Larmor frequency.
Is this an error?

Trying to clear things up, I checked the reference (Bloembergen et.al. 1947). Adding to my confusion, Figure 14 shows a saddle, but not really a dip near Larmor frequency for T2.

thanks and best wishes,
Allan

Dear Allan,
You are quite correct and the figures are in error. The SBM equations predict only a "shoulder" or "saddle" at the resonance frequency, not a dip. I have corrected them in the last update. Thank you for drawing this to my attention. It is by careful readers/students like you that the web site keeps getting better and better.
With appreciation
Allen Elster