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Result: Searchterm 'Rephasing'
found in 4 messages |
Result Pages: [1] |
More Results: Database (21) |
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N P
Fri. 18 Dec.09, 04:39
[Reply (5 of 12) to: '90 excitation pulse vs 180 inversion pulse' started by: 'Bjorn Redfors' on Sat. 27 Jun.09]
Category:
Basics and Physics |
90 excitation pulse vs 180 inversion pulse |
Ok. How about reading the thread before posting. We're not asking how a 180 rephasing pulse works. INVERSION VS REPHASING CONCERNING COHERENCE.
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n p
Fri. 11 Sep.09, 11:50
[Reply (3 of 12) to: '90 excitation pulse vs 180 inversion pulse' started by: 'Bjorn Redfors' on Sat. 27 Jun.09]
Category:
Basics and Physics |
90 excitation pulse vs 180 inversion pulse |
no hithesh n, that is a 180 rephasing pulse. thats not the question. the question is how is the net magnetization changed from the z plane to the -z plane without causing phase coherence, like the case of an inversion pulse. it is supposedly 2x as long or 2x as strong as the 90 degree pulse, but doesn't cause coherence. Why not is the question.
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Sam Shelly
Sun. 2 Nov.08, 23:02
[Reply (2 of 3) to: 'Regarding recovery and decay [basic phycisc]' started by: 'harry sanders' on Sat. 7 Jun.08]
Category:
Basics and Physics |
Regarding recovery and decay [basic phycisc] |
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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Reader Mail
Sun. 6 May.07, 17:28
[Start of: 'OVS & phase refocussing' 0 Reply]
Category:
Sequences and Imaging Parameters |
OVS & phase refocussing |
Why do we need to rephase spins in outer-volume regions after their excitation, still applying a crusher gradient afterward? Is this not too much work, rephasing and then dephasing them?
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