Hello fellow struggling MRI learners, don't worry if you don't understand the very last bit of the video about how to measure T1. It makes a lot more sense if you watch the rest of the series first. Best of luck!
@15:48 The student ask how to measure T1. It becomes apparent that this question was inserted in post editing as the audio is different and there is a student missing from the table. Most importantly, this section is confusing and I did not understand it because the instructor is using terms and processes that have not been yet described in previous videos (TR and TE).
6:20 In principle loss of coherence (transverse relaxation) can happen without loss of energy. 8:30 Mistake: NO it is not a logarithm grow it is 1-e(-t/T1). 18:51 He has not yet defined TE or TR but he uses both in explaining how to measure T1.
I skipped back to hear how TE came in and was like "THAT'S THE FOURTH TIME YOUR PHONE HAS GONE OFF PUT IT ON VIBRATE!!" Valid criticisms here I guess, consider them for the course, but excellent public good here, thank you.
Since the stronger magnets affect T1 by making it longer and minimize differences-- Q: Why bother with stronger magnetic field above 3T if it has affects that seems (as I understand) to minimize contrast? I really enjoy these videos! Thank you!
I have a question I can't seem to find anywhere, to anyone who can answer me (I'm Italian, so italian answers are also welcome). I understand that T1 and T2 are two different properties, the first one based on re-gaining of longitudinal magnetization (so, re-gaining of antiparallel precessing protons, taking B0 as the reference direction) and the latter based on losing of trasversal magentization (so, losing of phase coherence in the precession). But as different entities, how is there such a RF pulse that tilt by 90° the magnetization vector, so that the resulting transversal magnetization depends on the beginning longitudinal magnetization? Maximum longitudinal magnetization happens in resting condition, by the tiny difference in parallel and antiparallel precessing protons (6/10.000, as he says), while maximum transversal magnetization happens (i suppose) when the totality of the protons are in phase of precession. After a 90° RF pulse, parallel/antiparallel = 1 (so, parallel - antiparallel = 0, meaning that 6 protons over 10.000 swapped their verse) but I imagine that phase coherence involves much more than 6/10.000 protons. Why, if we apply another 90° RF pulse when longitudinal magnetizion has not totally recovered, the resulting transversal magnetization is also lower (meaning that not all the protons initially capable of gaining phase coherence gained it back)? Thanks to anyone who will answer (or at least, try to), it may be that some of my assumptions are wrong, correct me please if it is the case
TR is repetition time so time between first pulse and second pulse. for example in spin echo, where you're applying a 90 degrees pulse followed by a 180 degrees pulse, it would be the time between the first 90 degrees pulse and the second 90 degrees pulse. it's only in the case of repeating a sequence (which is often what happens in real life). TE is the echo time, so time between between pulse and when the echo happens. for context, echo is when there has been a recovery of phase coherence during T2 decay, due to the 180 degrees pulse flipping the protons. in spin echo, TE would be the time between the 90 degrees pulse and the peak of the echo, where you generally visualize your image. He doesn't explain those in this video, check video 15 for more info
Thanks for the awesome lecture Dr. Michael. My question is how are we detecting T1 relaxation from receiver coil, won't any coil in longitudinal direction will get overloaded with current induced by strong magnetic field. With Regards, Akshaykumar, Resident Radiology, Delhi
It is because of planes in which they are happening are in perpendicular directions! T1 is happening in longitudinal axis while T2 is happening in transverse axis. Bigger question is how are we detecting T1 relaxation, won't the receiver coil get overloaded by current?
There is (IMHO) a better explanation of how and why T2 and T1 vary in this video: ruclips.net/video/djAxjtN_7VE/видео.html Essentially, once the 90 degree RF pulse is sent, the precessions of all protons are in phase (i.e line up) with each other, and hence the individual magnetic moments of all the protons add up to form a macroscopic transverse rotating magnetic vector, rotating at the Larmor freq. However, over time, the some protons slip out of phase as they lose energy until all protons are precessing at different phase angles, and the net transverse field drops to zero. This is T2 relaxation. T1 relaxation is a different process, and occurs as protons which were knocked into the high energy state by the 90 degree pulse lose energy and fall back to the low energy state. As they do this, their magnetic moments start lining up with the background magnetic field, and hence build up the net longitudinal field. The lost energy is dumped into surrounding tissues as heat.
best ever series of lectures i have ever watched
what a time to be alive
Hello fellow struggling MRI learners, don't worry if you don't understand the very last bit of the video about how to measure T1. It makes a lot more sense if you watch the rest of the series first. Best of luck!
Henry H where are the rest of the lessons.?
@@jimmyjoepesci just check the channel. They have a playlist made of the entire course 🙂
@15:48 The student ask how to measure T1. It becomes apparent that this question was inserted in post editing as the audio is different and there is a student missing from the table. Most importantly, this section is confusing and I did not understand it because the instructor is using terms and processes that have not been yet described in previous videos (TR and TE).
6:20 In principle loss of coherence (transverse relaxation) can happen without loss of energy.
8:30 Mistake: NO it is not a logarithm grow it is 1-e(-t/T1).
18:51 He has not yet defined TE or TR but he uses both in explaining how to measure T1.
please, Do u have a good text book for such principles of mri?
Dr. Lipton is one my inspirational teachers, even I don´t know him in person.
I skipped back to hear how TE came in and was like "THAT'S THE FOURTH TIME YOUR PHONE HAS GONE OFF PUT IT ON VIBRATE!!" Valid criticisms here I guess, consider them for the course, but excellent public good here, thank you.
63% comes from 1 - 1/e.
Since the stronger magnets affect T1 by making it longer and minimize differences--
Q: Why bother with stronger magnetic field above 3T if it has affects that seems (as I understand) to minimize contrast?
I really enjoy these videos! Thank you!
Must have missed something in the break :( TR? TE? Hopefully becomes clearer later.
I think it is repetition time and echo time
Given the context I would say they're relaxation time and excitation time respectively.
Hello bonob0123. You can find documentation regarding the effect of TR and TE on T1 and T2 at this link: mriquestions.com/image-contrast-trte.html
I have a question I can't seem to find anywhere, to anyone who can answer me (I'm Italian, so italian answers are also welcome).
I understand that T1 and T2 are two different properties, the first one based on re-gaining of longitudinal magnetization (so, re-gaining of antiparallel precessing protons, taking B0 as the reference direction) and the latter based on losing of trasversal magentization (so, losing of phase coherence in the precession).
But as different entities, how is there such a RF pulse that tilt by 90° the magnetization vector, so that the resulting transversal magnetization depends on the beginning longitudinal magnetization?
Maximum longitudinal magnetization happens in resting condition, by the tiny difference in parallel and antiparallel precessing protons (6/10.000, as he says), while maximum transversal magnetization happens (i suppose) when the totality of the protons are in phase of precession.
After a 90° RF pulse, parallel/antiparallel = 1 (so, parallel - antiparallel = 0, meaning that 6 protons over 10.000 swapped their verse) but I imagine that phase coherence involves much more than 6/10.000 protons.
Why, if we apply another 90° RF pulse when longitudinal magnetizion has not totally recovered, the resulting transversal magnetization is also lower (meaning that not all the protons initially capable of gaining phase coherence gained it back)?
Thanks to anyone who will answer (or at least, try to), it may be that some of my assumptions are wrong, correct me please if it is the case
Can anyone explain what TR and TE is
TR is repetition time so time between first pulse and second pulse. for example in spin echo, where you're applying a 90 degrees pulse followed by a 180 degrees pulse, it would be the time between the first 90 degrees pulse and the second 90 degrees pulse. it's only in the case of repeating a sequence (which is often what happens in real life).
TE is the echo time, so time between between pulse and when the echo happens. for context, echo is when there has been a recovery of phase coherence during T2 decay, due to the 180 degrees pulse flipping the protons. in spin echo, TE would be the time between the 90 degrees pulse and the peak of the echo, where you generally visualize your image.
He doesn't explain those in this video, check video 15 for more info
Part of the video is missing
Thanks for the awesome lecture Dr. Michael.
My question is how are we detecting T1 relaxation from receiver coil, won't any coil in longitudinal direction will get overloaded with current induced by strong magnetic field.
With Regards,
Akshaykumar, Resident Radiology, Delhi
Faraday's law says EMF generated proportional to rate of change of mag flux, main mag field not changing.
Great explanation!
Is regain of longitudinal magnetization and decay of transverse magnetization a simultaneous process with respect to a single proton?
from what i understood yes, but not at the same rate. T1 recovery is much longer than T2 decay
If T1 and T2 are happening at the same time, how cannot they be symmetric, I found it confusing
It is because of planes in which they are happening are in perpendicular directions!
T1 is happening in longitudinal axis while T2 is happening in transverse axis.
Bigger question is how are we detecting T1 relaxation, won't the receiver coil get overloaded by current?
The "symmetry" is lost in time as well. T2 happens faster than T1.
There is (IMHO) a better explanation of how and why T2 and T1 vary in this video: ruclips.net/video/djAxjtN_7VE/видео.html
Essentially, once the 90 degree RF pulse is sent, the precessions of all protons are in phase (i.e line up) with each other, and hence the individual magnetic moments of all the protons add up to form a macroscopic transverse rotating magnetic vector, rotating at the Larmor freq. However, over time, the some protons slip out of phase as they lose energy until all protons are precessing at different phase angles, and the net transverse field drops to zero. This is T2 relaxation.
T1 relaxation is a different process, and occurs as protons which were knocked into the high energy state by the 90 degree pulse lose energy and fall back to the low energy state. As they do this, their magnetic moments start lining up with the background magnetic field, and hence build up the net longitudinal field. The lost energy is dumped into surrounding tissues as heat.
This makes so much sense, thanks dude.
Thanks dr
Good