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MRI Forum: Regarding recovery and decay ...
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  Category:  Basics and Physics
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harry sanders

Sat. 7 Jun.08,
12:59
Regarding recovery and decay [basic phycisc]
Hi there,

I'm studying on some basic MRI physics. And my study book tells me when the RF pulse has been switched of the amount of magnetisation in the longitudinal plane increases and at the same time but idependently the amount of magnetisation in the transverse plane decreases. I was wondering if some one could explain to me why these 2 parameters do not have an influence on eachother. It seems way more logic to me that the recovery of longitudinal plane is because of the decrease of transverse plane. Sorry for my bad english and I hope some one could give me an explanation!

Yours,
Harry

John Jackson

Fri. 12 Sep.08,
08:48
Hi,

I'm not so sure but I think because different physical process are being involved. Longitudal relaxation has got something to do with energy exchange to the environment. Transverse relation occurs because of spin dephasing (magnetic inhomogenity.)

John

Sam Shelly

Sun. 2 Nov.08,
23:02
Right on.

Recovery and delay are two separate physical processes like the last guy said. It had me stumped for a while when I was studying as well. But read carefully and think hard about it...

T1 recovery is the return of net magnetization into alignment with b0.

T2 decay is a totally different process and is, as the previous person said, simply loss of net magnetization in the transverse plain due to dephasing. The more electrons that are precessing in phase in the transverse plane, the stronger the NMV is in that plane. And, hence forth, when the RF pulse terminates, the influence of b0 gradually dephases the electrons in the transverse plane. As they dephase, the transverse NMV decreases accordingly, until the next pulse hits, rephasing the electrons and starting the process all over.

Hope that helps. MRI physics is hairy and boring at times. Load up on expressos to stay awake and stick with it, because studying MRI physics can be like taking a bottle of sleeping pills.

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