You have made understanding MR Physics so easy! Your sense of humour is icing on the cake. Feeling confident taking the ARRT after watching your videos. Thank you so much!
Thanks so much. 🎉 I have some stuck with this kind of knowledge. I have been reading many lectures about MRI. Could I ask you some question, Mister? 1. Some of people said that: The flip angle is determined by proportion of spin state "up and down" after exciting pulse. Is that correct? 2. After 90 RF pulse, a number of spin up will be equal to spin down. The spins which is resonated will be in phase. It is explained by quantumn machenics. But it seems to confuse me. Maybe is there something force them to be in phase? Also I don't know why 180 RF pulse cause it too. Somewhere in the internet, they explained understandably in the vector frame that the fast spin will catch up the lag spin and despend on the direction you put 180 pulse in. But when i try to apply it into the picture of spin-state, it makes me impossible to understand. 3. About 180 RF pulse in spin echo, after 90 exciting pulse, the transverse magnetization will gain conherence a little bit then dephasing with T2* decay. When we do a series of another 180 RF pulse, we have some coherence peaks. However, they gradually descrease magnitude and when we connect these peaks, we have T2 Decay. What make these peaks become smaller and smaller after 180 RF pulses. 4. After 90 RF pulse, we add a RF 180F Pulse. Now the vector B1 maybe >180? Is that mean the more spin up state becomes spin down? Could you do me a favor? 😭 I stuck with these problems a few days.
Thanks for the comment and great questions my friend! I think you are getting at a really frustrating point in that yes all of the physics governing magnetic resonance imaging are indeed covered by the laws of quantum mechanics, but trying to visualize what is going on at the quantum level is near impossible and for good reason! If the position and spin are mere statistical quantities resolved at measurement, how can we truly know their precise number and position/orientation? I think at best we can say a statistical number of these spins will be more aligned with the magnetic field B0 than randomly, our RF pulse will imbue a statistically higher number of these spins with a coherent precessional frequency and flip angle to produce a signal and so forth. But I think the visuals we use to depict these in a classical sense still hold a great degree of truth of what's going on. As to question #3, what makes the peaks become smaller is the ever increasing disorder of the system that begins as soon as we apply our initial RF pulse. Think of it like friction in the real world, we will always have irrecoverable energy loses with any system we put energy into whether it be your car or an MRI machine (excluding semiconductors!). We actually talk about this in the Turbo-Fast Spin Echo here: czcams.com/video/ZW7dw-zL9_M/video.html Hope this helps!
Thanks for this! I noticed at 6:23 in video you discussing spinning after RF pulse, wouldn't they be "wobbling" around a vector pointed in the y-xis? As opposed to circling all the way around like that? Sorry probably dumb question
No question is dumb, thanks for the commenting! It can be really hard to picture how this process plays out in 3D space but the axis of precession is the Z-axis. The net magnetizations in each voxel are vectors that can be oriented in any direction. At first, right after our initial RF pulse, they are aligned i.e. "in-phase", all precessing coherently about the z-axis, but naturally they begin pointing in different directions as time goes on and they became more and more disordered i.e. "dephased" but the axis of procession as a group remains the Z-axis. What is important when considering signal generation is how these vectors project into the XY-plane, as shown in the mentioned animation. Hope this helps!
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.
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 czcams.com/video/vK6PeCPpOLY/video.html 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.
Hey Dr TE, I've just started MRI and this series has been so helpful! Love your animations and your humour :D
Awesome to hear it's helping, check back later this week for a new episode!
Amazing!!! Best MRI lectures on CZcams!
Too kind! Thanks so much for commenting and the support!
You have made understanding MR Physics so easy! Your sense of humour is icing on the cake. Feeling confident taking the ARRT after watching your videos. Thank you so much!
So happy to hear they helped and thanks for putting up with all the bad jokes! Best of luck on your exam, you got this!
Your lectures are the best on CZcams yet. Thanks a million!
Too kind! Thank you so much for watching and commenting!
You coming clutch on my studies bruh!
Glad I could help!
Amazing video
Thanks for commenting!
Thanks so much. 🎉
I have some stuck with this kind of knowledge. I have been reading many lectures about MRI. Could I ask you some question, Mister?
1. Some of people said that: The flip angle is determined by proportion of spin state "up and down" after exciting pulse. Is that correct?
2. After 90 RF pulse, a number of spin up will be equal to spin down. The spins which is resonated will be in phase. It is explained by quantumn machenics. But it seems to confuse me. Maybe is there something force them to be in phase? Also I don't know why 180 RF pulse cause it too. Somewhere in the internet, they explained understandably in the vector frame that the fast spin will catch up the lag spin and despend on the direction you put 180 pulse in. But when i try to apply it into the picture of spin-state, it makes me impossible to understand.
3. About 180 RF pulse in spin echo, after 90 exciting pulse, the transverse magnetization will gain conherence a little bit then dephasing with T2* decay. When we do a series of another 180 RF pulse, we have some coherence peaks. However, they gradually descrease magnitude and when we connect these peaks, we have T2 Decay. What make these peaks become smaller and smaller after 180 RF pulses.
4. After 90 RF pulse, we add a RF 180F Pulse. Now the vector B1 maybe >180? Is that mean the more spin up state becomes spin down?
Could you do me a favor? 😭 I stuck with these problems a few days.
Thanks for the comment and great questions my friend! I think you are getting at a really frustrating point in that yes all of the physics governing magnetic resonance imaging are indeed covered by the laws of quantum mechanics, but trying to visualize what is going on at the quantum level is near impossible and for good reason! If the position and spin are mere statistical quantities resolved at measurement, how can we truly know their precise number and position/orientation? I think at best we can say a statistical number of these spins will be more aligned with the magnetic field B0 than randomly, our RF pulse will imbue a statistically higher number of these spins with a coherent precessional frequency and flip angle to produce a signal and so forth. But I think the visuals we use to depict these in a classical sense still hold a great degree of truth of what's going on.
As to question #3, what makes the peaks become smaller is the ever increasing disorder of the system that begins as soon as we apply our initial RF pulse. Think of it like friction in the real world, we will always have irrecoverable energy loses with any system we put energy into whether it be your car or an MRI machine (excluding semiconductors!). We actually talk about this in the Turbo-Fast Spin Echo here: czcams.com/video/ZW7dw-zL9_M/video.html
Hope this helps!
@@MRIPhysicsEXPLAINED I'm really grateful to you. Hope your channel would be well-known ❤️❤️❤️
Hello from Kazan, Russia!
Big thanks for your videos!!!
Hello there and thanks for commenting! Cheers from the USA my friend!
Waiting for new video on turbo fast echo sequence
In the works my friend!
Thank you so much pro
Thank you, new lecture coming soon!
Extremely good content 🎉 thanks
Thanks for commenting and watching!
Thanks for this! I noticed at 6:23 in video you discussing spinning after RF pulse, wouldn't they be "wobbling" around a vector pointed in the y-xis? As opposed to circling all the way around like that? Sorry probably dumb question
No question is dumb, thanks for the commenting! It can be really hard to picture how this process plays out in 3D space but the axis of precession is the Z-axis. The net magnetizations in each voxel are vectors that can be oriented in any direction. At first, right after our initial RF pulse, they are aligned i.e. "in-phase", all precessing coherently about the z-axis, but naturally they begin pointing in different directions as time goes on and they became more and more disordered i.e. "dephased" but the axis of procession as a group remains the Z-axis. What is important when considering signal generation is how these vectors project into the XY-plane, as shown in the mentioned animation. Hope this helps!
Thank you!! What I needed was to go back to your earlier excellent videos on t1 and t2 decay contrast from about a year ago 😅
@@RobertWilliamsserving Awesome glad they helped!
How the hell do I understand this now??
I ask myself this daily when it comes to MRI Physics 😂
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.
I’m just saying this as a fan so that you can improve your channel
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 czcams.com/video/vK6PeCPpOLY/video.html 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.