I am radiographer who undergoes training in MRI recently! Your channel is very helpful to me as which makes the difficult physics less horrifying !Thankyou
Your videos are a blessing. I remember all the hard work trying to figure out by myself quantum physics (for dummies 😂😅) in order to understand MRI physics when I was applying to radiology residency. Also your illustrations and animations are very pretty
Your videos are so helpful! I was having difficulty learning MRI physics alone from a book, and your videos have been a game changer. You make mri physics so easy to understand. You’re a great teacher!! Thank you!!
Thanks @meemsisme! Comments like this really make my day 🙌. That's exactly why I started this channel - the textbooks are so dense and often concepts seem more difficult than they really are!
You are the best!!!! coming from a psychology background with a least knowledge in physics and had to learn it for my fmri course. You are saving lives man
I really love your videos. I'm trying to get more used to the MRI terms and concepts because I decided to narrow my studies a little bit more. I'm a biomedical engineering student in Brazil and most of the things about these topics are in English. It took me a lot of time to manage Reading and listening to the articles and academic books in English. But your videos are crystal clear and helped me a lot. ❤ I already had MRI classes at college, but now, I can understand the big picture a lot better.
Thank you for your video series! A lot of my PhD project involves MRI physics, and this is the perfect refresher for the course I did last year--and taught extremely well! Most textbooks are overwhelming and very maths heavy, but I'm picking up more of the theory here and visualisations than I did in class :)
I'm so glad you've found it helpful! I started the channel because I found that information from textbooks was taking so long to digest! Good luck for your PhD 👍
Great video as always! Making a difficult concept easy to understand with analogies and amazing diagrams! Been following you since earlier this year and now you've achieved worldwide fame on Radiopaedia! You are a hero and inspiration to radiology trainees across the world. Hope you're not overworking yourself - must be time intensive making all this content.
I proudly reached this episode and cant wait to see the rest, your way of clarifying the points is special, a big respect ♥️ Will you explain CT next?🌹
Thank you for this amazing videos sir ❤ it helped a lot to understand what MRI actually is and its mechanism. Eagerly waiting for the upcoming videos 😊
Really impressive videos that clearly explain difficult to apprehend concepts in MRI physics! Thanks a lot for doing this for us! Could you please try to explain why nuclear spins precess around the Z-axis instead of just aligning themselves strictly parallel? Thanks in advance!
Thank you! Precession is caused by a quantum property of the hydrogen known as spin angular momentum. Because the hydrogen has a non-zero spin (non-zero inherent angular momentum) it will precess in an external magnetic field. There are some videos around where the process is explained using a bicycle tire and the gyromagnetic angular momentum of the tire causes precession (with gravity being the external magnetic field). And I find this is a good physical model to conceptualise the process of precession in the quantum world. As to why particles have these properties? Who knows?
@@radiologytutorials I am a new student in medical physics and I have a lesson about MRI and its function.you cant imagine how it was difficult for me and made me feel too bad. Your videos make everything completely clear for me and you dont know how much I feel comfortable with my lesson and all of this is because of your videos. Thank you so much
quick question! when the protons align in the transverse plane when rf pulse is applied, the protons do not physically flip to 90 degrees rather it is the same amount of parallel to anti-parallel protons precessing in phase which causes the NMV to be in the transverse plane. Is this correct?
Excellent question. In short, yes, the protons do not physically flip. The net magnetisation vector as a whole reacts in the bounds of classical physics principles. In the quantum realm (at proton level) we cannot assume any specific orientation or magnetic moment for an individual proton/spin (Heisenberg uncertainty principle). It’s useful to think of it as you have described, protons precessing in phase but even this has limitations - which starts to go beyond my level of understanding. Hope that helps 🙂
Hi Chelsea. Plan is to have them done by this Friday. I’ve been frantically working on it to make it perfect (hence no video here for the past three weeks). Will make a post here on TH-cam when it’s ready. Thank you for your support 🙂
Happy holidays Dr. Nel. I was wondering about the RF pulse, because I hear some people talk about the RF pulse as though we are sending electromagnetic radiation in the radio wave range, and some people talk about it in the sense that we are turning on and off the RF coil at a frequency that is in the same Hz range as radio waves, and so no electromagnetic radiation, just a magnetic field that resonates with the precession frequency. But then some say electromagnetic radiation is a magnetic field because electroMAGNETIC... Could you help me win an argument, I mean, understand what an RF pulse actually is? As always, thank you for tutorials no one deserves but everyone needs.
How many videos u r planning for MRI and CT sir...just to have a bare idea since my exams are starting next month and ur videos are very helpful for preparing radiology physics 🙏🙏🙏
How does the magnetization vector go past 90 degrees? Is there a second RF pulse applied when it’s at 90degrees. It doesn’t seem to make sense that the angle the protons can be flipped can be larger than the vector of the transverse magnetization force
Excellent question! A 90 degree RF pulse is a specific pulse strength for a specific period of time. If we were to increase the duration or the strength then the spins would pass 90 degrees. At first this makes no sense. Why would spins pass full transverse magnetisation? Difficult to answer in text but I'll try! The answer lies in quantum theory. When we place a hydrogen (with non-zero spin) in a magnetic field it will align with the magnetic field either in parallel (low energy) or antiparallel (high energy) direction. At any given moment the spin can exist in both the parallel and antiparallel states. On average slightly more will be parallel. Which gives us our net magnetisation vector. When we talk about flipping spins we are in fact talking about the net magnetisation vector. The RF pulse is adding energy to the system and causing resonance. The added energy allows more spins to fall in the antiparallel (higher energy state). This is the basis for how the net magnetisation vector can flip past 90 degrees. I wish I could draw a diagram but I hope that is a good start for understanding. Feel free to ask more if it still doesn't make sense! Michael
I have one question sir...Can you please explain in details why those protons showing higher and lower energy states to allign parallel and antiparallel directions? It will be very helpful.
Difficult to explain in a comment but I’ll try. Any atom with a non-zero spin value will have what’s known as a magnetic moment (it is useful to think of the atom as a small bar magnet) due to the atoms inherent spin angular momentum. Much like a bar magnet will align with a magnetic field, so will atoms with a non-zero spin. Where it gets more difficult to understand is why do these atoms lie in both the parallel and antiparallel directions. This is due to the quantum mechanical properties of the protons. This is definitely beyond the bounds of this course. Protons can have what is known as spin up and spin down (which determines the alignment in a magnetic field). It seems illogical that some protons would naturally align in a higher energy state - this energy comes from thermal energy (which is the reason the absolute number of protons in each state is dependent on temperature). It gets more complicated than this still. Any proton at any given point in time can exist in both the parallel and antiparallel states until measured (kind of like Schrödinger’s cat 🐈⬛) This is known as Heisenberg Uncertainty principle. I’m not doing the physics any justice with this explanation, but if you are interested I would suggest reading further into quantum theory. Warning it gets weird, very weird..
I was struggling with this concept too. While researching, the quantum physics was getting weirder and weirder. I found one explanation that said "it's just easier to stay parallel because it requires less energy/effort...others wont simply follow this and will stay antiparallel" haha at this point I stopped trying to understand why this really happened and just learnt it that way
Not sure I understand your question fully. But hopefully this helps. Hydrogen protons in fat and water will only resonate when the RF pulse frequency matches the precessional frequency. The rate at which the net magnetisation vector reaches 90 degrees is the same (for water and fat). You are correct that water and fat have slightly different precessional frequencies in the same magnetic field- therefore only those with the frequency that matches the RF pulse will resonate. We use an RF pulse that actually has a range of frequencies (bandwidth) which will ensure water and fat at the same location will resonate. When we talk about relaxation, as you mention in the second part of your question. This only occurs once the RF pulse is turned off. Then, there is definitely a difference between the rates at which water and fat dephase. This dephasing/ loss of transverse magnetisation (T2) has to do with the spin spin and spin lattice interactions in the different tissues (this has nothing to do with the RF pulse and this is what contributes to T2 contrast in the image). Hope that helps a little 🙂
The flip is due to protons resonating in phase. You are right, if an RF pulse is applied for long enough the flip past 90 degrees is due to spins existing in higher energy (antiparallel) states.
can someone Please explain why the Protons suddently are in Phase? do only those protons get flipped that accidently share the same phase and all the rest is getting left out? or is the energy of the RF impuls big enough to allign all the Protons of the same Frequenzy ?
The slice selection gradient causes protons to precess at different frequencies along the z axis (head to toe of the patient). Only protons precessing at the same frequency as the frequency as the radiofrequency pulse will start to resonate in phase. These protons will be at the same location (slice) along the z axis due to the slice selection gradient. Spins that are precessing at a different frequency to the radiofrequency pulse will not precess in phase and the net magnetisation vector will remain in the longitudinal plane. Not sure if that answers your question.. let me know
@@radiologytutorials thank you so much for the answer. But my problem is that in the same voxel, same lamor frequenzy, same Material, they precess at different phases. So what causes them to all go in phase. If it is the radio frequency that forces them all in phase I don't understand how. Only explanation I can imagine is if you blow at something that is spinning it either goes faster or changes direction if you hit it in the wrong moment. So only the protons that are already in phase by accident get flipped and all those that are in a different phase don't get flipped by RF Impuls because they are in the wrong position. So can you please explain how it really happens?
Okay i found an answer that satisfys me: Based on 'hanson._concept_mri_2008_quantum', the reason why the precessions appear to be in phase after the RF impulse is because they aren't. The RF impulse is not able to change the phase of the precession or the spin. However, it can change the energetic probabilities of the energy states, which alters their net direction, as if they are flipped. Then, the main magnetization vector is rotated by 90° relative to the B0 vector. But the spins are still precessing around the B0 vector, hence the relaxation." @@radiologytutorials
has anybody reading this comment happen to take their registry and PASS after watching these videos?? along with reading your school books and other study sources? My test is 11/2
Man it's impressive enough to understand these concepts, but to be able to explain them so clearly is simply on another level.
Haha, thanks mate!
Omg yes 🙌🏼
I am radiographer who undergoes training in MRI recently! Your channel is very helpful to me as which makes the difficult physics less horrifying !Thankyou
Great to hear. That's the goal. Make physics less horrifying!
You are so great. You answered to all comments. 👍✌️👊
Your videos are a blessing. I remember all the hard work trying to figure out by myself quantum physics (for dummies 😂😅) in order to understand MRI physics when I was applying to radiology residency. Also your illustrations and animations are very pretty
Im from India, We dont have much develpoed educational institutes as your illustrations are.
Thank you Teacher ❤
Your videos are so helpful! I was having difficulty learning MRI physics alone from a book, and your videos have been a game changer. You make mri physics so easy to understand. You’re a great teacher!! Thank you!!
Thanks @meemsisme! Comments like this really make my day 🙌. That's exactly why I started this channel - the textbooks are so dense and often concepts seem more difficult than they really are!
Finally this is making sense! Brilliant videos you are a great teacher!
Excellent! that's all I can ask for. Hope it continues to make sense throughout the course 😊
You are the best!!!! coming from a psychology background with a least knowledge in physics and had to learn it for my fmri course. You are saving lives man
What an explicit tutorial 👏
Thank you very much for this great MRI physics series. My professor could definitely learn something from your teaching skills!♥
Oh wow! Thank you. That’s very generous. I’m glad this has been helpful 🙂
I really love your videos. I'm trying to get more used to the MRI terms and concepts because I decided to narrow my studies a little bit more. I'm a biomedical engineering student in Brazil and most of the things about these topics are in English. It took me a lot of time to manage Reading and listening to the articles and academic books in English. But your videos are crystal clear and helped me a lot. ❤
I already had MRI classes at college, but now, I can understand the big picture a lot better.
Thank you for such a lovely comment! Love hearing about people's journeys to the channel 🙌
Thank you for your video series! A lot of my PhD project involves MRI physics, and this is the perfect refresher for the course I did last year--and taught extremely well! Most textbooks are overwhelming and very maths heavy, but I'm picking up more of the theory here and visualisations than I did in class :)
I'm so glad you've found it helpful! I started the channel because I found that information from textbooks was taking so long to digest! Good luck for your PhD 👍
Great video as always! Making a difficult concept easy to understand with analogies and amazing diagrams!
Been following you since earlier this year and now you've achieved worldwide fame on Radiopaedia! You are a hero and inspiration to radiology trainees across the world.
Hope you're not overworking yourself - must be time intensive making all this content.
Thank you so much for such a lovely comment! Lucky to be doing something I'm passionate about 🥳
You are seriously awesome. The way you explain things is marvelous. keep going.
That's so kind! Thank you for your support 🤗
I proudly reached this episode and cant wait to see the rest, your way of clarifying the points is special, a big respect ♥️
Will you explain CT next?🌹
I’m cross training into MR and these free videos are sooo much better than the course I paid for ❤
Very useful explanation! Gracias from Spain.
Very useful video sir ....u made it too easy to understand ❤thanku so much
Its so great to understand suxh difficult topics with this ease
I'm learning so much from you, thank you for these awesome videos. Im so shocked at the quality especially because this is FREE
I'm so glad they've been helpful!
Sir in this lecture I’m getting clear idea on transverse and longitudinal magnetisation……🙏.powerful concept in simple words.
Thank you. It should keep getting clearer over time. Hope you’re well Dr Kumar 🙏🏻
Thank you for this amazing videos sir ❤ it helped a lot to understand what MRI actually is and its mechanism. Eagerly waiting for the upcoming videos 😊
Thank you so much. I'm so glad you are finding this series useful. Working hard on the next videos 🙂
You are amazing man. Now I fully understand it.
Really impressive videos that clearly explain difficult to apprehend concepts in MRI physics! Thanks a lot for doing this for us! Could you please try to explain why nuclear spins precess around the Z-axis instead of just aligning themselves strictly parallel? Thanks in advance!
Thank you! Precession is caused by a quantum property of the hydrogen known as spin angular momentum. Because the hydrogen has a non-zero spin (non-zero inherent angular momentum) it will precess in an external magnetic field. There are some videos around where the process is explained using a bicycle tire and the gyromagnetic angular momentum of the tire causes precession (with gravity being the external magnetic field). And I find this is a good physical model to conceptualise the process of precession in the quantum world. As to why particles have these properties? Who knows?
Your lectures on Physics are quite amazing. Will you be making same kinda videos on nuclear medicine physics?
Thank you! The plan is to cover CT next then move on to nuclear med 🙂
I dont know how I say you thank you. your video is impressive great. I am really happy finding your channel.
I’m so glad you found the channel 🙌🏼 thank you for taking the time to comment ❤️
@@radiologytutorials I am a new student in medical physics and I have a lesson about MRI and its function.you cant imagine how it was difficult for me and made me feel too bad. Your videos make everything completely clear for me and you dont know how much I feel comfortable with my lesson and all of this is because of your videos. Thank you so much
You are amazing explaining that
quick question! when the protons align in the transverse plane when rf pulse is applied, the protons do not physically flip to 90 degrees rather it is the same amount of parallel to anti-parallel protons precessing in phase which causes the NMV to be in the transverse plane. Is this correct?
Excellent question. In short, yes, the protons do not physically flip. The net magnetisation vector as a whole reacts in the bounds of classical physics principles. In the quantum realm (at proton level) we cannot assume any specific orientation or magnetic moment for an individual proton/spin (Heisenberg uncertainty principle). It’s useful to think of it as you have described, protons precessing in phase but even this has limitations - which starts to go beyond my level of understanding. Hope that helps 🙂
@@radiologytutorials thank you for your response! Ive been watching your videos to study everyday! Please keep posting
Amazing course. What tool do you use for your animations?
Love the videos and appreciate them greatly but I was curious if you'll be uploading the MRI question banks soon? Thanks!
Hi Chelsea. Plan is to have them done by this Friday. I’ve been frantically working on it to make it perfect (hence no video here for the past three weeks). Will make a post here on TH-cam when it’s ready. Thank you for your support 🙂
Thanks doctor.. Points noted... See you in the next tutorial
See you there!
Thanks for superb lectures, looking forward to the next one! 😍
Next one will be out on Monday 👍🏼 planning on getting 3 out per week. Thanks for watching!
Thank you very much
Superb expplaination
Thank you ☺️
Thank u so much 🙏🙏
Pls, Do video on CT physics
Happy holidays Dr. Nel. I was wondering about the RF pulse, because I hear some people talk about the RF pulse as though we are sending electromagnetic radiation in the radio wave range, and some people talk about it in the sense that we are turning on and off the RF coil at a frequency that is in the same Hz range as radio waves, and so no electromagnetic radiation, just a magnetic field that resonates with the precession frequency. But then some say electromagnetic radiation is a magnetic field because electroMAGNETIC... Could you help me win an argument, I mean, understand what an RF pulse actually is? As always, thank you for tutorials no one deserves but everyone needs.
How many videos u r planning for MRI and CT sir...just to have a bare idea since my exams are starting next month and ur videos are very helpful for preparing radiology physics 🙏🙏🙏
Probably about 20-25 MRI videos. Not sure yet for CT but they won’t be out before your exam 😖
Okay sir...Thank you so much for your kind reply
Much awaited. Thank you Sir.
Thank you and we are hopeful for further lectures🙏
Can you make videos about : ultrasound physics, flouroscopy physics and contrast media as well ? So educatory videos thanks.
Hey!i m unable to find video 1 and 2 on MRI physics?
The hydrogen atom also has an electron why doesn't the total magnetic moment cancel out?
does higher gyromagnetic ratio increase S/N ratio?
How does the magnetization vector go past 90 degrees? Is there a second RF pulse applied when it’s at 90degrees. It doesn’t seem to make sense that the angle the protons can be flipped can be larger than the vector of the transverse magnetization force
Excellent question! A 90 degree RF pulse is a specific pulse strength for a specific period of time. If we were to increase the duration or the strength then the spins would pass 90 degrees. At first this makes no sense. Why would spins pass full transverse magnetisation? Difficult to answer in text but I'll try!
The answer lies in quantum theory. When we place a hydrogen (with non-zero spin) in a magnetic field it will align with the magnetic field either in parallel (low energy) or antiparallel (high energy) direction. At any given moment the spin can exist in both the parallel and antiparallel states. On average slightly more will be parallel. Which gives us our net magnetisation vector. When we talk about flipping spins we are in fact talking about the net magnetisation vector.
The RF pulse is adding energy to the system and causing resonance. The added energy allows more spins to fall in the antiparallel (higher energy state). This is the basis for how the net magnetisation vector can flip past 90 degrees.
I wish I could draw a diagram but I hope that is a good start for understanding. Feel free to ask more if it still doesn't make sense!
Michael
@@radiologytutorials thank you for the response. This is my second time going through your course and its making more sense to me now!!
Thanks a lot sir, 🎉
👌🏼
I have one question sir...Can you please explain in details why those protons showing higher and lower energy states to allign parallel and antiparallel directions? It will be very helpful.
Difficult to explain in a comment but I’ll try. Any atom with a non-zero spin value will have what’s known as a magnetic moment (it is useful to think of the atom as a small bar magnet) due to the atoms inherent spin angular momentum. Much like a bar magnet will align with a magnetic field, so will atoms with a non-zero spin. Where it gets more difficult to understand is why do these atoms lie in both the parallel and antiparallel directions. This is due to the quantum mechanical properties of the protons. This is definitely beyond the bounds of this course. Protons can have what is known as spin up and spin down (which determines the alignment in a magnetic field). It seems illogical that some protons would naturally align in a higher energy state - this energy comes from thermal energy (which is the reason the absolute number of protons in each state is dependent on temperature). It gets more complicated than this still. Any proton at any given point in time can exist in both the parallel and antiparallel states until measured (kind of like Schrödinger’s cat 🐈⬛) This is known as Heisenberg Uncertainty principle. I’m not doing the physics any justice with this explanation, but if you are interested I would suggest reading further into quantum theory. Warning it gets weird, very weird..
I was struggling with this concept too. While researching, the quantum physics was getting weirder and weirder. I found one explanation that said "it's just easier to stay parallel because it requires less energy/effort...others wont simply follow this and will stay antiparallel" haha at this point I stopped trying to understand why this really happened and just learnt it that way
Thanks ✨
Pleasure Diego!
Thank you doc❤ muah
Thanks doc! 🧡🧡
Pleasure 🧡
Is the Resonance time for the protons in fat and water the same?
Not sure I understand your question fully. But hopefully this helps.
Hydrogen protons in fat and water will only resonate when the RF pulse frequency matches the precessional frequency. The rate at which the net magnetisation vector reaches 90 degrees is the same (for water and fat). You are correct that water and fat have slightly different precessional frequencies in the same magnetic field- therefore only those with the frequency that matches the RF pulse will resonate. We use an RF pulse that actually has a range of frequencies (bandwidth) which will ensure water and fat at the same location will resonate.
When we talk about relaxation, as you mention in the second part of your question. This only occurs once the RF pulse is turned off. Then, there is definitely a difference between the rates at which water and fat dephase. This dephasing/ loss of transverse magnetisation (T2) has to do with the spin spin and spin lattice interactions in the different tissues (this has nothing to do with the RF pulse and this is what contributes to T2 contrast in the image).
Hope that helps a little 🙂
Thanks a million ❤ You explain it a million times better than my lecturer
Is the flip the result of some Protons now being anti-parallel, because they absorbed the energy applied?
The flip is due to protons resonating in phase. You are right, if an RF pulse is applied for long enough the flip past 90 degrees is due to spins existing in higher energy (antiparallel) states.
can someone Please explain why the Protons suddently are in Phase? do only those protons get flipped that accidently share the same phase and all the rest is getting left out? or is the energy of the RF impuls big enough to allign all the Protons of the same Frequenzy ?
The slice selection gradient causes protons to precess at different frequencies along the z axis (head to toe of the patient). Only protons precessing at the same frequency as the frequency as the radiofrequency pulse will start to resonate in phase. These protons will be at the same location (slice) along the z axis due to the slice selection gradient. Spins that are precessing at a different frequency to the radiofrequency pulse will not precess in phase and the net magnetisation vector will remain in the longitudinal plane. Not sure if that answers your question.. let me know
@@radiologytutorials thank you so much for the answer. But my problem is that in the same voxel, same lamor frequenzy, same Material, they precess at different phases. So what causes them to all go in phase. If it is the radio frequency that forces them all in phase I don't understand how. Only explanation I can imagine is if you blow at something that is spinning it either goes faster or changes direction if you hit it in the wrong moment. So only the protons that are already in phase by accident get flipped and all those that are in a different phase don't get flipped by RF Impuls because they are in the wrong position. So can you please explain how it really happens?
Okay i found an answer that satisfys me: Based on 'hanson._concept_mri_2008_quantum', the reason why the precessions appear to be in phase after the RF impulse is because they aren't. The RF impulse is not able to change the phase of the precession or the spin. However, it can change the energetic probabilities of the energy states, which alters their net direction, as if they are flipped. Then, the main magnetization vector is rotated by 90° relative to the B0 vector. But the spins are still precessing around the B0 vector, hence the relaxation." @@radiologytutorials
Thanks Dr
You’re welcome 😊
Super ❤
Thank you ❤️
May I ask if you know anything about studying radiology in Canada for international students (undergraduate)?
Ooft. Sorry, don’t know anything about it 😖
@@radiologytutorials it’s okay + thank you so much for your tutorials. They helped me with my anatomy final exam 🤍
Sir do you plan for fluro and mammo lectures.
Absolutely 💯
@@radiologytutorials Thank you Sir
❤
❤❤
F
has anybody reading this comment happen to take their registry and PASS after watching these videos?? along with reading your school books and other study sources? My test is 11/2
Did u pass?
❤❤
❤️❤️
❤❤