MRI T1 Relaxation & Contrast EXPLAINED | MRI Physics Course Lecture 6

[@Minisynapse]

As someone with (apparently) a passion for pedagogy (I'm a phd student on psychology (neuroscience actually but formally psych)), much respect for taking this kind of an approach. You delve into the topic not from the traditional "tell it like they told you" approach, but instead you use your own journey and the difficulties on your path to isolate areas where misunderstandings and confusions occur, and avoid those issues by tackling them before they even emerge. This approach is very intelligent and kind of "pre-avoids" the crucial misunderstandings you clearly know might occur when delving into MRI physics. As much as I respect ALL educational content creators online, those who really nail the pedagogy garner the most appreciation because there's a very clear desire to help others not suffer like you did when you were learning. That is also my drive as an educator: to help others learn what I learned but not suffer as much as I did while at it...to make it easier, more enjoyable, entertaining, fascinating, intuitive. That's how I felt watching this too. I felt like I received very important heuristics for understanding T1 and T2 imaging and all the intricacies and points of confusion that might emerge, and I feel like you nailed the fundamentals and created a solid cognitive ground on which to stand on for your viewers. You are clearly aware HOW you comprehended MRI physics and are now sharing those lessons. Beautiful!

[@MRIPhysicsEXPLAINED]

A little lost for words, thank you so much for taking the time to write such a kind and heartfelt comment! It is hearing from people like you that makes the trials and tribulations of making these videos all worth it in the end and motivates me to produce more content and improve myself as an educator as well. I can tell from just your words and self reflection that you will be/are a great educator yourself. While some may pressure you to create lectures with clear bullet point beginning and ending objectives to follow, it's equally ok to start with an idea or passion and let your curiosity and creativity flow and craft a story to tell. If you put your heart into it, people will see that and connect, and you've got a fan here for any and all of your education endeavors!

[@joopvanbroekhoven]

I did a PhD on magnetic resonance (ESR and NMR) in 1967. MRI did not yet exist at that time. I am long retired from industry but this marvellous series is very interesting revival for me.

[@MRIPhysicsEXPLAINED]

Awesome to hear, one of the true early pioneers!

[@takauyamurengwa1250]

I'm grateful for your emphasis on grasping concepts,,, I had waited long for this great episode, so worth it. Looking forward to the next one

[@MRIPhysicsEXPLAINED]

Thanks so much for the support and glad it was helpful!

[@rik4351]

I love how little this focuses on the maths, which is a great point of confusion for myself. Students will get taught that the time to repetition is related to the T1 weighting because of some parameter in a formula, but it is never actually explained what the real world effect of that would look like. Great video series!

[@MRIPhysicsEXPLAINED]

Thank you! I struggled myself trying to piece together where these numerical T1 definitions fell into the imaging process until I realized we have no control over it, only TR!

[@chrisdao]

this is amazing! I've been watching a few different videos from different content creators and I love love love your videos, i especially like how you answer all of those werid silly questions because I for one sometimes get caught up on those tiny insignificant details and here you are explaining them in such an easy way. like you just said fooorget about the 63% and last week I was trying to think about the contrast i'll see at such and such times :D lol

[@MRIPhysicsEXPLAINED]

Thanks so much! So happy to the hear the videos have helped make the subject clearer and hopefully a little entertaining!

[@aaqibzyt]

On my only day off in a week after long ass duties i am watching these videos to understand how beautifully MRI works cuz it is so satisfying. Finally someone is calling out random bs definitions.

[@MRIPhysicsEXPLAINED]

That's about the greatest compliment you could give, thank you so much and glad you are enjoying them! I will eat my words a little because there is an explanation for the definition for T1 that I went into depth on in the first Q&A video here kzbin.info/www/bejne/aYvNnmStqquibK8, but still not really applicable for our images.

[@thepirl903]

Oh interesting, I hadn't considered that the animation of the of the T1/T2 relaxation vectors coming together at the same time gave the impression that they 'completed' relaxation simutaneously. That's a good catch, I'll have to fix that animation on those slides for future talks. Brilliant series mate! Cheers

[@MRIPhysicsEXPLAINED]

Oh wow, feel like I'm talking to one of my heroes here! Seriously thank you for the excellent videos on your channel, one of the only sources I've seen that pieces together the net magnetization, Larmor Frequency and magnetic induction with hands down the best animations. They actually were a major inspiration for my own videos and I hope you didn't mind me referencing a few of the clips (this was the only one I suggested a slight change to) and made sure to encourage everyone to see the original videos on your channel. I'm involved in a new project to support free radiology video education at radiofreedia.org/ (the site is only about 10% built so still in a very rough draft) but if you're interested, I would love to embed your videos in the physics section or any other educational videos you'd be interested in contributing. Thanks again for commenting and cheers to you too!

[@thepirl903]

Glad to hear they're helpful and was flattered to see them referenced here! There's definitely always things to improve so it's helpful to hear what parts raise questions - especially since I'm a physicist not a radiologist, heh. The free radiology education is a brilliant idea, would be happy to contribute in some capacity - keep me posted. Keep up the great vids mate!

[@MRIPhysicsEXPLAINED]

@@thepirl903 Awesome look forward to it! Let me work on the site a bit more and I'll let you know when it's in a more final form to get your thoughts. And if you don't mind, shoot me an email at [e-mail] when you get a chance for future communication. Thanks again!

[@MRIPhysicsEXPLAINED]

Hello again! I've uploaded your videos to radiofreedia.org, please check it out and let me know if you approve! Cheers

[@marcochiarini3168]

If all my MD professor ware like you I would definitely take seriously 100% attending. Thanks a lot!

[@MRIPhysicsEXPLAINED]

Such a nice comment, thanks so much and glad you are finding the videos helpful!

[@janeabdo4491]

once again amazing content, thanks for making my studying easier!

[@MRIPhysicsEXPLAINED]

Glad it helped!

[@tay2twimming]

Got my MRI physics exam tomorrow 😂😂😂 You‘re a life-saver! Greetings from Germany

[@MRIPhysicsEXPLAINED]

Cheers from the US and good luck on your exam!!

[@tay2twimming]

@@MRIPhysicsEXPLAINED thank you so much for the clear concise explanation. I‘m a visual learner and the animation helped me tremendously. I was hoping to find Lecture 7 but I guess I will have to wait 😂😅

[@shahadab6294]

Thanks a lot :) one question: is the energy produced from the protons re-aligning again with the external magnetic field is basically heat energy or an RF wave or mix of both?

[@MRIPhysicsEXPLAINED]

Mainly heat. Further info on this can be found in the article below! www.mriquestions.com/what-is-t1.html

[@ishitapatel4659]

amazing lectures, what a gem.

[@MRIPhysicsEXPLAINED]

Many thanks!

[@nikoulei5041]

Great video to clear out my confusions! Thank you!

[@MRIPhysicsEXPLAINED]

Glad it was helpful, thanks for the support!

[@Quazlyy]

Thank you for this amazing video series! I really helped me prepare for my MRI related Master's thesis. One note about the 63%. It's not as arbitrary as one might think. This definition allows us to write the relaxation curve as (1-e^(-t/T1)) (I'm disregarding some scaling factors here). If we plug in t=T1, we get 1-1/e, which is approximately 63%. The choice of the base 'e' could be seen as arbitrary, but it is quite natural in my opinion. The same argument can be made for T2 with 37%.

[@MRIPhysicsEXPLAINED]

Thanks for supporting and excellent point! Was jesting on this topic a little because it tends to cause great confusion on the imaging side when introduced but great to know it is based in logic!

[@MinaRahmani-dh4nx]

Your videos are awesome!!

[@MRIPhysicsEXPLAINED]

Thank you!!

[@canerozturk5977]

I didn't really understand one point about T1 signal. Why the second RF pulse gets us the signal from only the fully recovered portion of the longitudinal relaxation? Why doesn't it resets the situation to full transverse magnetisation? I thought the 90 degree RF pulse affected all protons in the area and excite them into transverse magnetisation.

[@MRIPhysicsEXPLAINED]

It can be really hard to visualize what's going on! Check out the lecture on "The Echo" which helps visualize this process better. kzbin.info/www/bejne/r6rRqn17odSFp5Y

[@tomways8332]

Struggling a bit here. Could you tell me why bone has a longer net-magnetisation relaxation time than CSF? Since CSF has more water molecules, therefore higher proton numbers, why does bone take longer when it has less of everything mentioned above? Shouldn't the more protons = longer time for them to relax? Yet bone has less and takes longer? This is why I'm confused, thanks.

[@tomways8332]

You mentioned bone has a low signal, which means that it spins very minimally, therefore producing less signal. Shouldn't this mean it should be faster than CSF to relax since CSF has more protons and produces higher signal? Thanks!

[@MRIPhysicsEXPLAINED]

Thanks for the comment and good question! I think the first thing to realize is that T1 recovery time is not directly related to the number of protons but is an intrinsic property to the tissue itself, relying not only on the protons in a tissue but the chemical structure they are in and the local environment. Here is a chart that shows examples of T1 recovery times and notice how they can be very different for muscle than say liver, both of which are "soft tissues" mriquestions.com/why-is-t1--t2.html As for the figures in the lecture, the bone is shown to highlight the differences in T1 times but this requires a bit more explanation. The fact is that cortical bone contains so few protons it appears black on MRI! Any signal you see in bone is mostly from the marrow, which is either fat or red blood cells. And a more subtle point, not all tissues will reach the same magnetization if you wait long enough. Remember this magnetization comes from slighty more protons being aligned with the magnetic field than against. If the substance starts off with much less protons, it will not build as strong of a net magnetization, and you will see very little signal, as in the case of cortical bone. Thus, bone is drawn as a much smaller curve, with a much smaller net magnetization built over time than the rest of the tissues. Does this help?

[@pantrywarriors9577]

I am a bit confused, does T1 itself contribute to the image? Does the literal physical process of T1 recovery induce a current in the coils?

[@MRIPhysicsEXPLAINED]

Not significantly. Try to think of T1 recovery as the potential energy of the system. To induce current, we need both to have built up this magnet within the body and then for it to rotate or "precess" via our RF pulse. It is the rotation of this magnetic vector which causes the coil to see a varying magnetic field which then induces the current via Faraday's law, and the amount of current generated will depend on how big of an internal magnetic we've built. The magnetic vector is then lost due to T2 decay, i.e. the nice proton alignment we initially built up becomes randomly aligned again. T1 "recovery" is the process of realigning the protons again with B0, rebuilding our potential energy. Now since every voxel of tissue will undergo this rebuilding process at different rates, if we apply our next pulse before we give all the voxels enough time reach their full strength, we will generating varying currents for each voxel based on differences in their T1 recovery time. This is why we can build a contrasted picture derived from T1 recovery times. Note that if we wait long enough before applying our RF pulse so that each voxel achieves its maximum magnetic potential, we won't have T1 contrast! I know this is a lot to explain through words but if you haven't seen it yet, I think the next video illustrates this process well visually! kzbin.info/www/bejne/pKm0eHWPi6-oo6c

[@27Denty]

🎉🎉

[@clown8170]

Thank you

[@MRIPhysicsEXPLAINED]

Thanks for watching!

[@amlevi1726]

can't wait for next lecture! to bad my DWI and perfusion tecniques exam is two weeks from now! :D

[@MRIPhysicsEXPLAINED]

Thanks for the support and be sure to check out the channel tomorrow! (hint hint)

[@jakobthomsen1595]

Very well explained! BTW the 63% looks suspiciously like 1-exp(-1)

[@MRIPhysicsEXPLAINED]

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]

@@MRIPhysicsEXPLAINED Neat!

[@TAHA-TOUABA-RADIOGRAPHER]

Thank you very much pro

[@9678willy]

lettice

[@MRIPhysicsEXPLAINED]

😂