Introducing MRI: Generating an NMR Signal: Resonance and Excitation (7 of 56)
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- čas přidán 22. 09. 2014
- www.einstein.yu.edu - The seventh chapter of Dr. Michael Lipton's MRI course covers Generating an NMR Signal: Resonance and Excitation. Dr. Lipton is associate professor radiology at Albert Einstein College of Medicine and associate director of its Gruss Magnetic Resonance Research Center.
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Amazing lecture as always. Thanks Dr. Lipton.
Great clarity and pace, thank you!
Phenomenal lecture series! Thank you!
this explanation is masterful. An Electronic Engineer right here working with imaging systems. I never expected to be actually studying anything health related, but i gotta say this is very interesting...
thank you soooo much for putting these lectures here.they r saving my life :) i am a masters student of medical imaging but i hv started my studies after 8 yrs so i was struggling with my basic knowledge of physics .these are great thanks again :)
As an MRI student i find this presentation extremely helpful and enhancing to what i know so far.
Essential Oil Diffusers can u teach me how or help im pay u actual money for showing me how real scan works and demonstrate what’s in the software like siemens or Ge and how to know if there is motion or not
@@AaBb-xh9ds Most text books give an easier explanation. Also i'm not sure about explaining the software. I don't want to give you wrong information. I graduated last year from MRI school and i still have bit of a fresh idea of how things work. I would say google has a lot of free information. Go on MRImaster.com . Also MRI-q.com helped me, there are many reliable websites to help with your questions.
I hope that helps ...
Thank you sir for this great explanation.. I'm a Radiography student and this helped me alot to attend my exam very well.. Thank you so so much sir 🙏🏻🥰
18:00 Actually the E would also ring (very softly) because E is a harmonic of C meaning it is produced in the overtones of the note. But a tuning fork is designed to minimise harmonics so the E tuning fork would only resonate for a few seconds.
Thanks a lot Professor! Extremely helpful
Very clear explanation. Thank you so much
These videos help a lot.
You talk about the voltage from the coil: are there datasets available with that voltage data? I'm looking for something before k-space.
Really amazing lecture!
I would have a question: the net magntization vector is tilted via forcing phase-coherence of the processing "magnets". Is the phase of the spins of E2 now aligned to the phase of the spins of E1 too? Or do they get aligned with a 180° shifted phase? If all phases are aligned regardless of the energy state, then the transversal vector should have a higher magnitude than the original non-tilted one, because now 100% of the protons contribute to it.
@ 13:33 E1 being a higher energylevel than E2 does not feel good. Review: @ 30:14.
Why the longitudinal protons aligned half -half antiparallel ( of course to cancel the longitudinal magnetisation,but how ?)
Sorry Dr Lipton, could I clarify, if you're adding B1 (the perpendicular STATIC magnetic field), wouldn't that change to axis upon which the protons rotate?
I didn't really catch why the protons suddenly precess in phase after the perpendicular RF pulse is applied and not before? what's the difference other than the direction?
Two questions:
1) let's say in a 1.5T machine, is B0 = 1.5T or B0 +B1=1.5 T ?
2) So basically MRI machine discriminates between water content of different tissues, right?
Something I don't understand is why cancelling out the longitudinal NMV (at 90 degrees) results in a transverse NMV that is the same magnitude as the longitudinal one? Why do the transverse components of the parallel and anti-parallel protons add up (at B1 maximum) to exactly the same magnitude as the longitudinal field at rest? Does anyone have a good explanation? Did I just miss something in the video?
It's simply not true. If there is no B1 and only B0, the macroMagMomZ = magMomOfOneProton * cos(alpha) * % * N, where alpha - precession angle, % - percentage of excess of protons oriented anti-|| (he said 6p/10k), N - total num of protons in the sample. If now we have turned on B1 and wait until macroMagMomZ becomes 0 such that macroMagMomR reaches the max, the macroMagMomR = magMomOfOneProton * %% * N, where %% - the percentage of protons that rotate in phase. If %% = 100%, then macroMagMomR = magMomOfOneProton * N.
Please correct me if I am wrong.
Why is it the transverse component that is having precession and not the longitudinal component
Great Concept.
Thank you for a fantastically clear lecture series. I know its an analogy with regards to individual spins but one thing I am not understanding is why the growth in transverse magnetization appears to be at the expense of the longitudinal component. If adding energy causes phase coherence, then as the transverse components of individual spins stop canceling out, I can see how there would be increase of the transverse component but I don't see why the longitudinal component would change or decrease because the vertical components should remain aligned. It seems there would indeed be rotation of the net magnetization vector but it would be due to the addition of a rotating transverse component to the existing longitudinal component and therefore could never become fully transverse or perpendicular or 90 degrees to Bzero. Am I missing something?
Thanks for the reply. I'm not sure I quite follow but its plain that the rotation of the net magnetization vector to 90deg requires another process than just phase coherence which by itself should not affect the longitudinal component. I think it has to do with the population shifting towards higher energy state which apparently points in the opposite direction to the the original net magnetization vector. Eventually you shift the population just so such that 50% point one way and 50% point the other canceling the longitudinal component. This wasn't immediately clear but I can dig it.
Did you found out if your theory is correct? (I mean that the sum of parallel and anti-parallel protons are exact the same. So it cancels out the longitudinal vector. That only leaves the transverse vector due to the coherence of the frequencies of the protons.
Does it also mean if a 180 degree RF-pulse was given, that every proton has a higher energy state? (Or that the vector sum is much more higher?)
@@tuanneman from what I understood, placing this amount of protons into a static B forces them to dispose their own magnetic field parallel or antiparallel to the B lines.
this comes out in an antiparallel grade, which is proportional to how much intense B is, but never reaches a transverse magnetisation, unless you hit the protons with supplementary resonance-coherent EM waves.
what I don't get to understand is, if we do have to components in the magnetisation, one parallel and the other perpendicular to the static field, why do we lose parallel component if we simply get to synchronise protons' precession. I hope to understand going further,
The longitudinal component doesn't matter. Whether its zero or present, it will not be measurable by the receiver coil (in the above case, the coathanger wire voltmeter), since its perpendicular to the coil and does not cut it while rotating
@@IndyMactavish Incorrect. The T1 signal is entirely based on the longitudinal component, of course it matters. It can't be measured directly from the perpendicular direction but it's definitely important. He talks more about T1 relaxation and how to measure it in parts 11 and 12 later.
czcams.com/video/PN8cHwamcJA/video.html Is it Ella or is it Memorex?! The ad is he is referring to at 15:40
Is the NMV parallel or antiparallel to the B? So far, throughout this lecture series, I have seen the NMV drawn antiparallel to B. From what I understand the NMV is caused by a small excess of low energy nuclei that are parallel to B.
Great lecture series so far. I have found it very helpful. Thank you.
Nevermind! I see this question was addressed in part 5. Thanks!
The lecturer is a little confusing.
There a three vectors: the external magnetic field B0 (1.5 T), the magnetic moment of the proton u, and the magnetic field of the proton due to its magnetic moment Bp. In lower energy state the z component of u is parallel to BO and the z component of Bp is "antiparallel" to B0.
The radio frequency (alternating B and E fields) interacts with the magnetic moment only, in classical physics there is no B B interaction (in quantum field theory it is a higher order interaction, very very weak).
👏🏽👏🏽👏🏽
OMG why couldn’t you have been my teacher
I had understand that under external magnetic field,more protons are aligned parallel, resulting in growing on net magnetization vector in z direction.when we give RF pulse,protons go to higher energy level and flip opposite direction,anti parallel and also bring protons in phase,this results in transverse magnetization which can be measured.Here we were told that there are more protons in antiparallel direction,6 in 10000 in 1.5 Tesla,thus NMV is very little but opposite direction of magnetic field or Z axis.i am confused 🤔
The M-vector can not be detected AS LONG AS it is parallel to the B-field. The B-field is in comparison to the M-field much bigger