T2 Relaxation, Spin-spin Relaxation, Free Induction Decay, Transverse Decay | MRI Physics Course #4
High yield radiology physics past paper questions with video answers
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Once flipped into the transverse plane by the radiofrequency pulse the net magnetisation vector starts to lose the transverse magnertisation. This loss is primarily due to spins dephasing over time (a proportion of transverse magnetisation loss is due to spins aligning with the main magnetic field). Dephasing occurs due to spin-spin interaction and transfer of energy. The time taken to lose 63% of the transverse magnetisation vector is known as the T2 constant. In reality the measured signal loss is faster due to magnetic field inhomogeneities. This decay time is known as free induction decay/ T2* decay. We will examine how using a spin echo pulse sequence can account for this loss of signal. We will also illustrate how changing TE (time of echo) will enhance or negate T2 relaxation differences in tissue and ultimately determine the T2 contribution to contrast in the image.
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Not sure if the question banks are for you?
If you're here, you're likely studying for a radiology physics exam. I've spent the last few months collating past papers from multiple different countries selecting the most commonly asked questions. You'll be surprised how often questions repeat themselves!
The types of questions asked in FRCR, RANZCR AIT, ARRT, FC Rad Diag (SA), ABR qualifying Core Physics and MICR part 1 are surprisingly similar and the key concepts remain the same throughout. I've taken the most high-yield questions and answered them in video format so that I can take you through why certain answers are correct and others are not.
Happy studying,
Michael
#radiology #radres #FOAMrad #FOAMed
Nobel prize award winner. You have my vote!!
Haha 🤣 Appreciate it!
binge watching these like a netflix series lol. Really great work, Dr. Nel. Thanks a lot for making these videos.
This whole playlist has been AMAZING!!! Each one covers the given topic better than any other videos I've seen AND does it in half the time. You are the best :)
Wow, thank you! That means a lot 😊
Amazing work , you have made MRI physics possible to me . Thank you
I'm so glad 🙌. Thanks for your support!
I've seen so many videos and this is the only one that has ever made sense! Thansk
That’s so good to hear!
😂in between the video, i get out off face, but after apply 180 degree magnetic field, finally catch up a little! Thank you for your efforts! Highly appreciated sir!
Haha, imagine we had a 180 degree pulse at our disposal 😯
you saved my life! now i understand it all so much better :) keep on enlightening us with your wonderful videos! THANK U !!!!!!!!!
I'm so glad! Thank you 🙂
Much awaited lecture, thanks a lot sir Michael 🎉
Hope it made sense 🤞🏼 T1 relaxation will be uploaded tomorrow 🎉
Perfect as always. well explained. thank you so much.
Wonderful analysis, thank you!
Thank you. That's very kind of you 😊
Interesting like always,cant wait next part T1 relaxation keep safe doc!
Thank you Bedilu ☺️ T1 relaxation will be out tomorrow. Glad they’ve been interesting
Great explanation..thank you for these lessons.
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Thank you for all the great videos! Is there a book that you follow for creating your lectures videos?
Thanks a lot for this explanation: it really helped me to better understand the concept!
That’s excellence to hear 🎉
Your knowledge and the ability to explain it are truly unparalleled. Thank you.
Wow, thank you! Glad you're enjoying the videos!
Thanks for this awesome video! Helped me understand
So glad it helped 🙌 thanks for your support
Superb lecture like always! Thanks 🙏🏻
Appreciate it Nick 👌🏼
Thank you for being amazing as always, this was well explained ! I had a little bit of confusion when you said that because of magnetic field inhomogeneity the spins are going to precess with different frequencies and thats why T2* are generated. but since we have different frequencies how do we send an RF pulse that will match these changing frequencies due to inhomogeneity and knock them out of the Z-axis to the x,y axis in the first place???
i think it is local inhomogeneity rather than a field effect and this would explain why there is local signal void associated with metal, etc.
I had a question! At the diagram at 15:50, looking at TE2 --> is this approximately when we have lost 63% of the signal and basically why we need to time our echo appropriately to get a good image? Also!! Thank you so much for these videos! I'm an MRT(R) from canada, a new graduate looking to take MRI in 2024, so these videos are a big help!! If you need any help vetting questions or writing new ones for your x-ray bank, let me know and I'd love to give back!
I'm studying chemistry in my masters now and your video was really helpfull, thanks a lot!
Great to hear!
Superb lecture
Thank you!
Why is it that a 180 degree RF pulse rephrases all the moments, but the transverse magnetization hits a ceiling at the T2 decay curve? If it is only an issue of how long the RF pulse is on for, then why would having it on for the duration of a 90 degree pulse restore full transverse magnetization and break the ceiling of the T2 decay curve. Something quantum? As always, thank you!
Hi 👋 Not quite sure what you're asking exactly. The 180 degree pulse will only cause rephasing of spins if a previous 90 degree pulse has been applied prior. The first 90 pulse flips the spins in to the transverse plane. The spins will then decay at T2* - some will dephase faster than others depending on tissue type. If we then apply a 180 degree pulse the spins that dephased faster will now be lagging behind the spins that had slower T2* decay. This allows the faster spins to catch up with the slower spins at the TE when the spins will be in 90 transverse plane. If we were to only apply a 180 degree pulse as our first RF pulse the spins would flip a full 180 degrees and have no transverse magnetisation. They will decay at a rate of T1 (ie. regain longitudinal magnetisation) but have to T2 decay because there is no transverse magnetisation in the sample. This is actually a key feature of inversion recovery sequences which we will cover in two weeks time. I may be completely off what you were asking! Feel free to rephrase your question if I haven't answered it! Hope you're doing well!
If you're asking why can spins with a 180 RF pulse 'break through' the 90 degree angle (because surely once they resonate at 90 degrees and we continued to apply an RF pulse they wouldn't continue to flip to angles above 90) then yes you are right, this is due to a quantum property. It has to do with energy states of the spins (at resting state with just the main magnetic field spins are in two energy states - lying parallel [low energy] and antiparallel [high energy]). In the quantum world the spins can exist in both states until measured. Continuing the RF pulse for a longer period of time adds energy into this system and allows the a slight majority of spins to now exist in the antiparallel state (higher energy), therefore they are flipping past the 90 degrees. I hope I'm making some sense, very difficult to explain in text 😅
This was exactly what I was trying to understand, watching again with your explanation really helped! Thank you for the detailed response!
Sir , can you explain bulk magnetization of mri
Thanks so much for your great exaplanation and videos. When 180 pulse applied , the slower spin will be trailing behind the faster spin right. How they catch up ? Couldnot understand that concept
Practically when do you apply the 180° flip for a T2 weighted image? T2 relaxation is 63% of transverse signal loss. Do we then flip it when the T2* relaxation signal is at 37%? Is there an automated mechanism that does that because the fewest radiology technicians can react within milliseconds. Also the time T2 is different for different tissues. If the flip was done as I figured which of the 37% signal times(T2 of muscle, fat, CSF) would we take for the T2* flip?
Can I use your animations and slides for teaching purposes? Best MRI course I came across❤
Another question for you! At 15:00-15:50... you said this basically that we flip to 90 degrees and turn off the RF pulse and immediately sample. this is where I'm confused.... I thought the TE was when we... flip to 90 ... (wait) ... flip to 180 ... (wait) = TE. and sample here! so am I understanding this right? basically this explains the contrast differences between different tissues.... flip to 90 ... (wait 1 second) ... flip to 180 ... (wait 1 second) TE. and sample here! = small differences / all white flip to 90 ... (wait 2 seconds) ... flip to 180 ... (wait 2 seconds) TE. and sample here! = appropriate differences lets say at 37% transverse mag left. flip to 90 ... (wait 5 seconds ) ... flip to 180 ... (wait 5 seconds) TE. and sample here! = small differences / all black, no signal. in all of these examples we found the T2 values of the tissues souly based on the spin-spin interactions because we applied an RF pulse, waited some time (A), applied a second 180 RF pulse and waited that exact same time(A) and sampled the data. am i understanding this correctly?
Sir I want to buy a complete MRI course if you have
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Do video on CT scan physics 🙏
Once I've finished the MRI series, I will move on to CT
@@radiologytutorials ok. Sir
At 12:36, your explanation does not make sense. I mean both fast and slow spins are experiencing the same changes in their phase, so nothing changes and the leading one will remain the leading again. Could you please explain a bit ?
What a shit!!! Amazing explaination😱
I think that the video shows something that doesn’t really makes sense. In the longitudinal plane the net magnetisation vector is not processing because the individual atoms’ spins are out of phase. If somehow they were IN phase the Net magnetisation vector would have been processing in the exact way you show at the Course 3 11:15 minute. So, I m thinking that when the B1 magnetic field is applied, it turns the net magnetisation vector at the transverse plane, But now, we have every atom processing IN phase and this leads to the movement of the now vertical Net magnetisation vector. This movement I think should be the same with the one you show at the course 3 11:15 as a mentioned before and not as the rotational movement you show at the video. Showing the NET vector changing direction (becoming continuously parallel and anti parallel with the B1) doesn’t make any sense to me. I’m a medical student and I’m trying to figure it out so please, answer if you can. Thank you, your videos help too much!
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