Introducing MRI: Excitation and Frames of Reference (8 of 56)

Рет қаралды 64,688

9 жыл бұрын

www.einstein.yu.edu - The eighth chapter of Dr. Michael Lipton's MRI course covers Excitation and Frames of Reference. Dr. Lipton is associate professor radiology at Albert Einstein College of Medicine and associate director of its Gruss Magnetic Resonance Research Center.

Пікірлер: 16

@palmtreebeautiful 9 жыл бұрын

Thank you so much for sharing this!! Dr. Lipton is such a great teacher.

@loukasstergioulas7518 6 жыл бұрын

One thing is not clear to me. How is the transverse magnetization lost ( which means dephasing of the protons ) when we keep the B1 magnetic field on for longer time so that we pass the 90 degrees flip angle to go to 180 degrees? It is suppopsed that the RF pulse is at the Larmor frequency so it should keep the protons in phase .By the way ,thank you for sharing this video.

@MarcinDrozd 3 жыл бұрын

How is it possible to pass the 90 degree angle? I can't understand it...

@Medical_Electronics_Horizon 4 жыл бұрын

Thanks Doctor for this excellent knowledge sharing

@shoratnazari7755 5 жыл бұрын

Yes, I thought all sources said that it aligned PARALLEL to B - zero! Ken thanks for asking this question! Tyler - thanks for clarification

@clydez1234 Жыл бұрын

I can't understand why the transverse magnetization would be equal to the original longitudinal magnetization...

@abbbee8918 2 жыл бұрын

I think everyone has the same questions and I have never been able to understand what happens after 90 degrees and am completely mystified as to what happens beyond 180 and 360 etc. I understand the idea of phase coherence and how resonance brings this about. I also understood from other sources that an increasing proportion of protons are forced into the higher (anti parallel) state by taking on this energy, but he hasn’t explained it like that. Even so I am a long way off understanding what is actually going on. Any help would be greatly appreciated

@wesslesyt3304 Жыл бұрын

they actually use a 180 degree RF pulse when doing a spin echo sequence (T2*) it flips the NMV 180 degrees

@user-yy4pi3bw3u 2 жыл бұрын

What happen to transverse magnitization if we turn B1 on more than 90 ?

@wesslesyt3304 Жыл бұрын

well they use 180 degree pulses for T2* (spin echo scans) this is the only one i know of

@user-yy4pi3bw3u Жыл бұрын

@@wesslesyt3304 Spin echo not used for T2*

@kiwiboy4458 4 жыл бұрын

what does he mean by “around the static magnetic field ?”

@TheOlgaStudio 4 жыл бұрын

He means around the axis of the B0 externally applied magnetic field, I suppose he called it static because, unlike the perpendicular B1 magnetic field, it doesnt change its direction in time (B1 does as to cause aligned precession)