MRI basics: part 2 : alignment and precession

In part 2 of my MRI series, I discuss how an external magnetic field affects the magnetic moment of the hydrogen nucleus.
In particular, how it aligns and precesses.
Both are explained at length in a non technical fashion
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[@githice]

This was exemplary demonstration of the elusive MRI physics, my saviour as I get into Medical Imaging Equipment science exam, be blessed

[@burgertblom2733]

This is an excellent video. Usually people neglect the beta spin state in representations of the magnetization vector, and also do not explain incoherence. This explains it perfectly and also the link between T1 and T2 relaxation.

[@panchamiop3117]

this was just incredible.....loved it...thanks so much for this video

[@eduardosoccer7]

Thank you for your video. You made it look easy.

[@drmksu38]

I don't know how to say this video is wonderful 🤦🏻‍♀️❤️❤️❤️❤️😩شكرا

[@interwebzful]

the cage around the head is not to keep them still but to send RF energy, sometimes to receive it too, depending on design

[@AA-hi7ic]

Thank you so much for this video! It’s didactically perfect, even for people with no background in physics!

[@yidinggui8468]

Wonderful explanation! really helpful!

[@esmeraldaelhamzawy9114]

Wow you're the best illustrator ever, I loved how you used the toy to illustrate spin!

[@PhysicsHigh]

Thanks for your feedback.

[@saraahmed632]

Thank you so much for the video. This was a very good explanation and I understand this whole topic much better now.

[@PhysicsHigh]

Glad it helped.

[@sudheershamsudheensudhi5822]

Thankyou so much for this use full vedio

[@platinramadani3335]

Thank you for the great video! I have 1 question: why do the magnetic moment vectors not actually align exactly with the vector of the magnetic field that is applied? In other words, why does it actually "wobble" why doesn't it just stand still in 1 direction? Is it some quantum physics reason that I don't know or is it that you just converge to that optimal state the stronger the applied magnetic field is?

[@badrlinux6786]

Great Job, thankyou please give us more video about basics of MRI

[@PhysicsHigh]

Have you seen the others in the series? You watched video 2 in a series of 5

[@souad_joubbane]

An Arabic poet said: Stand up for the teacher and glorify him... He could have been a messenger... thank you so much for all your videos..

[@PhysicsHigh]

Thankyou for your kind feedback.

[@curiouscat8396]

Can U please do one on the Stern-Gerlach experiment. How do half of those valence electrons/silver atoms get aligned antiparallel?

[@semorgh2854]

Is it possible to make a video about: if we spin a mole of Proton Isotopes what would be the total magnetism B0. Thanks in Advance.

[@curiouscat8396]

Ah, yes, but, how do some of these protons get aligned antiparallel, in the first place? Must the 2 protons in the H2O have opposite spin, due to Pauli exclusion principle? If so, then the only protons left over, to align parallel, are the H+ & OH- ions, neutrons in the heavy water not having much of a magnetic moment.

[@autmanmansour6996]

In one of his lectures on MRI, Dr. Michael Lipton mentions that the net magentic moment vector is antiparallel to the external magnetic field, could you please comment on that?

[@PhysicsHigh]

Woo am I to argue with Dr Lipton, but all the texts/sources I have found state that the net magentic moment vector is parallel, since there are more parallel that antiparallel when aligned in an external field

[@whyurlapsmellsgood69]

Clarification since I heard this somewhere else. The vectors going directly left and right or directly front and back in the parallel direction don’t cancel out right? They just add to the net vector.

[@PhysicsHigh]

If you have two vectors that are 180° to each other, then they will cancel out however, most of these vectors are not like this. The components that are directly opposite (horizontal )to each other or cancel out but they will have also vertical components that are in the same direction giving a net result in the vertical direction.

[@sywaddr11]

Do we have a sayingon what cause proton and neutron spin?

[@DarrenReynoldsBly]

In the first video you explained that protons don't literally spin; it's a historical term. Yet in this video, you explain about precession using a spinning gyroscope, and begin to explain the phenomenon caused by the radio pulse. How is the second video reconciled with the first, please?

[@PhysicsHigh]

The fact that it processes gives rise to the inference that it seems to have the property of spin, although they actually don’t physically spin.

[@4pharaoh]

If the atoms are free to move, why precess? Why do they just not align fully with the magnetic field? In your example one end of the gyroscope is fixed ridged, we could say it does not want to precess but you force it by making one end rigid, (if not with the table then with gravity). Secondly,why align parallel AND anti-parallel, surely a free particle will flip so that it is no longer anti-parallel. I may just be thick. Good video though, thanks.

[@AEPalo]

Good questions. I'm not the uploader but I highly suggest checking out a paper titled "Is Quantum Mechanics necessary for understanding Magnetic Resonance?" by Lars Hanson, specifically page 8. You should be able to find a free copy of the pdf online.

[@PhysicsHigh]

When the B field is applied the atoms never align perfectly. There will always be a small angle deviation from the B field. That will result in the precession. The parallel vs antiparallel is a quantum effect. The ratio between them is very similar. Almost 50:50. However there is a slight difference (less) due to anti parallel being at a higher energy level. That results in s NET amount being parallel.

[@jns3255]

Great videos, but where's part 3!!?

[@PhysicsHigh]

part 3 will be published 27 Feb, part 4 and 5 are in the works

[@jns3255]

Hi. Thank you. Great videos thanks for making them

[@sinethakmeemana1911]

4:46 could you please explain the table smack

[@PhysicsHigh]

+Sineth Rajawasam haha. It's a editing cue which I didn't cut out.