2 жыл бұрын
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@dem890 6 күн бұрын
Thank you so muchh.
@MRIPhysicsEXPLAINED 2 күн бұрын
Thanks for watching! New video coming this weekend!
@Lethmyr_ 6 күн бұрын
Doesn't the precession happen as soon as the protons enter the magnetic field? A combination of the field b0 and the spin angular momentum of the protons cause them to precess. The RF pulse just tips the alignment of that precession and causes phase coherence. In other words how would the lamor frequency work if the protons did not already precess at that frequency?
@MRIPhysicsEXPLAINED 6 күн бұрын
These are good questions, and as always with MRI physics there are layers of ever finer details you will find the more specific you try to understand it. When we talk about precession in MRI physics, what we're really referring to is the precession of the net magnetic vector. Yes, the individual protons precess about their axis when put into a magnetic field. You don't even need an MRI machine, we're in a magnetic field right now on Earth. But does this generate signal in our MRI machine? So we need to get these individual precessing protons aligned, and with enough energy from our magnetic field, we can cause more to align with the field than the random orientations caused by the background kinetic energy. This is what builds our net magnetic vector, and it doesn't necessarily mean all the individual protons are in phase with each other, but there is a net magnetic vector due to their alignment. The RF pulse then tips all of these aligned protons off the B0 axis, and they precess together at the larmor frequency, generating our signal. It is the dephasing of the orientation that causes our signal loss. Check out this article for more information: www.mriquestions.com/how-does-b1-tip-m.html
@Pk-xh9wg 18 күн бұрын
Nice video. ❤🎉
@MRIPhysicsEXPLAINED 15 күн бұрын
Thanks for watching and commenting!
@lucaya 20 күн бұрын
Lectures up until now were great but this one sucks. The animations are just too hard to understand, also you said the refocusing pulse is ninety degrees to reverse the direction of the rotation of the magnetic vector you have to flip 180 degrees, so more hydrogen ions generally pointing opposite the B zero field instead of in the same direction.
@lucaya 20 күн бұрын
I’m just saying this as a fan so that you can improve your channel
@MRIPhysicsEXPLAINED 20 күн бұрын
Ha I will be the first to admit my animations are rudimentary and not the best, and this is a very difficult subject so not quite sure how to present this in a different way but the key point is if we're able to invert the spins with a strong enough RF pulse, the receiver coil will see a reversal of the spins that causes rephasing of our spins and signal. The screw example at the end is the most tangible example of this I could think of. This is just to get a grasp on what's going on before proceeding to the pulse sequences, starting with the spin-echo sequence kzbin.info/www/bejne/rHyZgZh5hdWCgrs where we flush out this idea out a little more so maybe check out that video and see if it helps further clear up these concepts.
@karthikraju6286 20 күн бұрын
Why larmor frequency for csf and fat is different 5:50
@MRIPhysicsEXPLAINED 20 күн бұрын
This is because we have changed the magnetic field across the x-axis so that the CSF voxel see a different field strength than the fat voxel, and remember that the Larmor frequency is directly related to the magnetic field strength for each voxel. Hope this helps!
@lucaya 21 күн бұрын
Great thanks
@MRIPhysicsEXPLAINED 20 күн бұрын
Glad it was helpful!
@lucaya 21 күн бұрын
Excellent!
@MRIPhysicsEXPLAINED 20 күн бұрын
Thanks for watching and commenting!
@michaelwinkler8047 23 күн бұрын
Great thanks
@savsvolumetricvisualizatio6150 23 күн бұрын
Great!
@MRIPhysicsEXPLAINED 22 күн бұрын
Hope it helped and thanks for commenting!
@michaelwinkler8047 23 күн бұрын
Great work!
@MRIPhysicsEXPLAINED 22 күн бұрын
Thank you! Cheers!
@michaelwinkler8047 23 күн бұрын
Great lecture thank you.
@MRIPhysicsEXPLAINED 22 күн бұрын
Thanks for watching and commenting!
@marcochiarini3168 26 күн бұрын
Grate video!!
@MRIPhysicsEXPLAINED 22 күн бұрын
Thank you!
@marcochiarini3168 27 күн бұрын
Amazing video
@MRIPhysicsEXPLAINED 27 күн бұрын
Thanks for commenting!
@marcochiarini3168 27 күн бұрын
If all my MD professor ware like you I would definitely take seriously 100% attending. Thanks a lot!
@MRIPhysicsEXPLAINED 27 күн бұрын
Such a nice comment, thanks so much and glad you are finding the videos helpful!
@marcochiarini3168 27 күн бұрын
Amazing video
@MRIPhysicsEXPLAINED 27 күн бұрын
Thanks for watching!
@zer0legend109 28 күн бұрын
This perplexing, I got to know how to calculate it when there is only a phsse shift, but how do we go calculating it when there is also a frequency shift at the time we measured the signal
@MRIPhysicsEXPLAINED 27 күн бұрын
The frequency localizing gradient is not a shift but an encoding of different frequencies along the x-axis. Since we create this gradient magnetic field, we know which frequencies should be where spatially along the frequency encoding axis, so we when we break our raw signal down into frequencies via the Fourier Transform, we get this information. Check out the dedicated frequency encoding lecture here for further info if you haven't already: kzbin.info/www/bejne/eorNYoaCg9Wjh68
@marcochiarini3168 28 күн бұрын
Amazingly beautiful
@MRIPhysicsEXPLAINED 27 күн бұрын
Thank you! Cheers!
@AmitJoshi-fu4ir Ай бұрын
Add Fourier transform and K space lecture.
@MRIPhysicsEXPLAINED Ай бұрын
Right around the corner, stay tuned!
@oscarlubega Ай бұрын
this is amazing work...... and i have seen many teachings on ADC/DWI
@MRIPhysicsEXPLAINED Ай бұрын
Glad to hear it was helpful and thanks for commenting!
@PrashathSiva Ай бұрын
❤
@MRIPhysicsEXPLAINED Ай бұрын
😊
@franciscofernandomoralessa8344 Ай бұрын
Thanks for this amazing set of lectures; Question... in the Noa image when the hand pokes the vectors I understand in whats its said that only after the poking of the protons start to precess, or that move already exist before the stimulation?
@MRIPhysicsEXPLAINED Ай бұрын
Hello, thanks for commenting and great question! While the individual protons will have some baseline spin like all atoms and particles, they are not precessing all together as one. We need to impart them with some angular energy with our RF pulse to get them precessing as one unit together. Hope this helps!
@kalogerakisbookings1336 Ай бұрын
Great work!
@MRIPhysicsEXPLAINED Ай бұрын
Thank you! Cheers!
@Theextremepessimist Ай бұрын
I have to watch these videos more than once.
@MRIPhysicsEXPLAINED Ай бұрын
Me too 😂
@palpytine Ай бұрын
Well, now, you just had to go and introduce FLAIR. As I'm sure you must be aware, that now means you're contractually obliged to cover *all* the common inversion recovery sequences.
@MRIPhysicsEXPLAINED Ай бұрын
😂 It's been a lingering around in the back of my mind somewhere, but first have to wrap up this diffusion weighted imaging series! Next up, DTI
@TaejinMin-q3p Ай бұрын
This is EPIC!
@MRIPhysicsEXPLAINED Ай бұрын
😂
@EriqHover Ай бұрын
niceee
@MRIPhysicsEXPLAINED Ай бұрын
Thanks for watching!
@tsrmstefanobiagini 2 ай бұрын
Great video, could you make a video about difference between monopolar and bipolar dwi and on the meaning of 3 scan 4scan 3diagonal gradients (siemens) Thank you!!
@MRIPhysicsEXPLAINED 2 ай бұрын
Will definitely put it on my radar, thanks for watching and commenting! Nearing the final stages of the next lecture on DTI, should be a good one so stay tuned!
@Pendergeist 2 ай бұрын
I really vibe with these videos and your sense of humor
@MRIPhysicsEXPLAINED 2 ай бұрын
Thank you! Hopefully can bring a little entertainment to an otherwise dry subject!
@t1relaxation 2 ай бұрын
I noticed that the T1 relaxation times are constant. So does the MRI tech choose the TR time only to control TE or does the tech choose both TR and TE? I'm taking the ARRT test in December 2024
@MRIPhysicsEXPLAINED 2 ай бұрын
In general, the chosen TR time will affect T1 image contrast, and the chosen TE time will affect T2 image contrast and these values will remain constant for that sequence. For most sequences, these parameters are all ready chosen and optimized so the technologist simply picks the appropriate "protocol" to run. However, you can certainly manually go in and change the values of TE and TR, albeit this will change the contrast of the picture and you'll likely get an angry call from your local radiologist :)
@jakobthomsen1595 3 ай бұрын
Wow, that's fascinating! Thanks for explaining this!
@MRIPhysicsEXPLAINED 2 ай бұрын
My pleasure!
@jakobthomsen1595 3 ай бұрын
Really cool 🙂
@MRIPhysicsEXPLAINED 3 ай бұрын
Thanks again for commenting!
@jakobthomsen1595 3 ай бұрын
cool 🙂
@MRIPhysicsEXPLAINED 3 ай бұрын
Thank you!
@jakobthomsen1595 3 ай бұрын
Great video series! Ok, so if I understand correctly the magnetization recovery process can be described (omitting constants) by a differential equation f'(t)=1-f(t) where t is time, f'(t) is the re-magnetization rate which is proportional to 1-f(t) i.e. the difference missing to "fully magnetized", where f(t) is the current magnetization proportion (1 meaning 100% magnetized). Because the constant 1 vanishes when taking the derivative f'(t) must be -f(t) which means it must be the exponential function with negative exponent: f'(t) = -e^-t and f(t) = e^-t, because the exponential function is the only function that is its own derivative. And to account for the re-magnetization speed or respectively the re-magnetization time we introduce a scaling factor 1/T1. Which gives us the full formula 1 - e^(-t/T1). And because this function approaches 1 i.e. full re-magnetization only in the limit t -> infinity, we choose some finite time instead. With t/T1 = 0 meaning full de-magnetization the next obvious choice is to choose t/T1 = 1 i.e. t = T1 which gives us 1-e^-1 = 1-0.37 = 0.63 approximately. Phew, I think I got the math part 🙂
@MRIPhysicsEXPLAINED 3 ай бұрын
You got it my friend! With those math skills you might want to get into this teaching hobby as well!
@sameerchandorkar365 3 ай бұрын
Thanks
@MRIPhysicsEXPLAINED 3 ай бұрын
Wow thank you so much!! Your support really means a lot, working on the next lecture now as we speak so stay tuned!
@jakobthomsen1595 3 ай бұрын
Very well explained! BTW the 63% looks suspiciously like 1-exp(-1)
@MRIPhysicsEXPLAINED 3 ай бұрын
Thanks for commenting! I actually did a deep dive on this 63% and did a little segment on it in the Q&A video here, check if out if you'd like to learn more kzbin.info/www/bejne/aYvNnmStqquibK8
@jakobthomsen1595 3 ай бұрын
@@MRIPhysicsEXPLAINED Neat!
@minakshi2412 3 ай бұрын
Great video.. you made it super interesting to learn, thank you!
@MRIPhysicsEXPLAINED 3 ай бұрын
Awesome to hear it helped, thanks for commenting!
@julessoto137 3 ай бұрын
STRONG WORK. Thank you
@MRIPhysicsEXPLAINED 3 ай бұрын
Thanks for watching and commenting!
@DrMdAbdulHafeezMalik 3 ай бұрын
It was easiest explanation I have encountered till now ,Plz post more videos
@MRIPhysicsEXPLAINED 3 ай бұрын
More are in the works!
@DrMdAbdulHafeezMalik 3 ай бұрын
Thank you y
@MRIPhysicsEXPLAINED 3 ай бұрын
Glad it helps and thanks for the comment!
@MRIPhysicsEXPLAINED 4 ай бұрын
LINK TO CLINICAL FLOW CHART 👇👇👇 radiofreedia.org/approach-to-abnormal-restricted-diffusion/
@Obscure121gw 4 ай бұрын
Local AM radio stations operate between 540 and 1700 kHz, not 68 MHz. FM radio stations operate between 88 and 108 MHz which is slightly higher than your example of a 1.5T magnetic field.
@MRIPhysicsEXPLAINED 4 ай бұрын
Thanks for the comment. This (should have been) already corrected with a caption that pops up during this segment saying the band is analog TV and into the FM range.
@sehrish9847 4 ай бұрын
Waiting for more videos.Excellent explanation.
@MRIPhysicsEXPLAINED 4 ай бұрын
Thank you! More videos are in the works!
@KokebGebremeskel 4 ай бұрын
This is truly Amazing! Thank you so much!
@MRIPhysicsEXPLAINED 4 ай бұрын
Thanks for watching and commenting!
@interwebzful 4 ай бұрын
that was good
@MRIPhysicsEXPLAINED 4 ай бұрын
Thank you!
@keegansimyh 4 ай бұрын
Question: how were we able to localize in the Z-X plane before when we were also using gradient magnetic fields in both these axes?
@MRIPhysicsEXPLAINED 4 ай бұрын
Hello, check out the lectures on slice selection kzbin.info/www/bejne/rGnNiGuBZt5ggac and frequency encoding kzbin.info/www/bejne/eorNYoaCg9Wjh68 where we go in-depth on how to localize the signal in the Z and X dimensions in you haven't already. If you still have questions let me know!
@keegansimyh 4 ай бұрын
@@MRIPhysicsEXPLAINED I'm confused about why we don't get the same problem at 7:55 in the Z-X plane. I can see that using frequency gradient in the X and Y axes causes the same frequencies to repeat and thus we can't resolve along (x+y=c). But why do we not get the same problem when using frequency gradient in both the Z and X axes? How are we still able to resolve voxels along those diagonals?
@MRIPhysicsEXPLAINED 4 ай бұрын
The beautiful thing about the slice select gradient technique is that we don't have to resolve the signal in the z direction, the gradient is turned on along the z-axis so that when we apply our RF pulse and tune it to the region of the body of interest along the z-axis, we know all the signal we receive is coming from that slice alone. We simply just then turn off the z-axis gradient, the protons in the slice fall back into precession at the Larmor frequency, and the problem then turns simply into localization along the x and y axes for which we do the frequency encoding and phase encoding techniques. Now in 3D MRI acquisition we do replace this slice select gradient technique with a true image encoding gradient along the z-axis, but that will require a little extra knowledge to understand which we'll cover in future lectures 🙂
@RayJacobsenJr 4 ай бұрын
As an MRI Field Service Engineer, it is my job to ensure that all the intricate MRI Physics are functioning properly every day. I'm grateful for the "MRI Physics EXPLAINED" channel on KZbin, now I can direct people with questions to this resource. Your efforts are much appreciated, please continue to create valuable content.
@MRIPhysicsEXPLAINED 4 ай бұрын
Thank you for the comment and for keeping these amazing machines running! We've got a whole set of advanced lectures coming that will get into some engineering topics so stayed tuned!
@josephdays07 4 ай бұрын
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@MRIPhysicsEXPLAINED 4 ай бұрын
Hello, thank you for sharing!
@MRIPhysicsEXPLAINED 4 ай бұрын
LINK TO CLINICAL FLOW CHART 👇👇👇 radiofreedia.org/approach-to-abnormal-restricted-diffusion/
@karlitadr11 4 ай бұрын
Thank you, I appreciate your pedagogy and humor!!🧠😂💯 KEEP IT GOING!!!
@MRIPhysicsEXPLAINED 4 ай бұрын
Much thanks!! Check out the channel this weekend for a NEW lecture!