MRI Slice Selection | Signal Localisation | MRI Physics Course #7
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- čas přidán 27. 06. 2023
- High yield radiology physics past paper questions with video answers
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We've spent the last few videos looking at how signal is generated in MRI and how loss of transverse magnetisation and gain of longitudinal magnetisation provides contrast in an image. Over the next three talk we will discuss how signal is localised in a MRI slice. We'll start with slice selection in the z axis and then move on to frequency encoding and phase encoding gradients in the x and y axes respectively.
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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
This man deserves an award for how well he explains these topics and how helpful his videos are
exactly!
I dont think i have ever commented on a youtube video in my life. But i have to express my thankfulness for your videos and how you always give a recap/refresher to remind us on previous topics. I have my registry soon and these videos have been helping tremendously and can't thank you enough!!!
Thank you for commenting on this one! So glad these videos have been helpful 😊
Wow! The amount of effort I could imagine making this video is commendable. This is a very precise topic. I am really amazed how you have put your explanations into animations. I am really thankful to you for making this series. I am watching this again and again to get my concepts clear. Thank you very much!!!
agree. Cant imagine how much time it takes to make the various animations in your videos. Thank you so much looking forward to the entire MRI series as a radiology resident in the US
Thank you so much! It means the world to me that these videos are helping 🙂 Definitely makes the effort worthwhile 🙏🏻
How much time you have spent to make these incredible videos. I dont think you are doing this solely for the money. I cant believe how much satisfaction you are gaining by reading the lovely comments. I wish I had such brilliant ability to teach others. I wish you all the good luck in life Micheal. ❤
You have done for Radiology Physics what 3Blue1Brown did for Calculus! Hats off!!!!
I'm anaesthetic MRI lead clininician at my hosp.......and never really had a clue how the MRI worked 🙈 so thanks for this! Really appreciate how awesome everything is explained!
I'm so glad you found this helpful!
a MRI lover who loves to teach...thanks for great explanations ❣
You are so welcome!
Excellent work! You finally made physics easy to understand !
I'm so glad! Thank you!
Thank you so much !
Dude! Your program is 10x better than any book, or the MRI schooling I had 15 years ago. It's all due to the actual *moving* diagrams, as well as your brilliant explanations and analogies.
Just like some chrome extensions do (i.e. Adblock plus), you need to mention and post a link to submit donations, whilst keeping the actual videos free on CZcams. Unfortunately, I'm guessing that it might be a violation of CZcams's policies, but if not, you absolutely must do that. I'd give ABP donations occasionally over the years when they'd ask, and your material is much, much more deserving.
I wish I found your material earlier than several days before my exam. I couldn't find any decent CZcams pages on the subject before that. One, though explaining on a whiteboard well and myself thinking it was the best, didn't even get the basics of parallel vs anti-parallel correct. I just quit looking for alternatives after that.
Being that your material is much more recent and thus lesser known at the moment, I hope you pop up as the top search result as soon as possible to help others. Thanks.
TL;DR: YOUR MATERIAL MAKES MRI SCHOOLS OBSOLETE!!
Had I known about you and your channel, Michael, I would've done the ARMRIT exam earlier. I need to imagine all these things in my head for me to learn it and you made it happen. I'm taking my exam in a few weeks. More power to your channel and God Speed! You and your team are truly gifted. Thank you for sharing this to us.
I'm so glad the videos have been helpful! Best of luck with your exam. Please do let me know how it goes. Really appreciate your kind words 😊
These are all just absolutely fantastic.
Thank you Dalton!
Thank you sir. Your concepts are on point. It’ll be better if you can release more videos as we have our exams on 15th of july.
Who is this guy? I can’t believe I’m not only understanding but even enjoying this!
Thanks Doc
amazing video, mock exam in 2 weeks.. wont be able to finish revising by reading the books. This helps a lot. Thank youuu!!
Good luck with the studying Audrey! you've got this 🙌
Thanks a lot sir Michael, 🎉very much excited for this new video
Hope you found it useful! Thanks Fazal
Thanks a lot sir for conceptual understanding🙏🙏
Always a pleasure Sohail. Thank you!
This is wonderful explanation
Thank you. Really appreciate it 🙂
Thank you for such tremendous effort. The way of teaching is pretty clear. i have recommended your channel to my friend. (MRI Engineer)
Awesome! Thank you so much for spreading the word 🥳
Thank you!
i don't usually write comments, but this time i have to. you are great! this is so helpful. so thank you!
Wow, thank you. I’m glad it was helpful 🙂
Wonderfull, thank you!!
My pleasure! 🙂
Thanks a lot for the lecture, really helped refreshing my knowledge. One thing I find confusing is that your SSG-in-time graph implies that one would have the SSG turned on during the refocussing 180deg pulse. I can't seem to understand what the purpose is of using such configuration, given that the slice of interest was already selected after the 90deg pulse. I get the point of the 180deg pulse but I don't understand why we'd use a gradient here again, could you maybe elaborate on this? Respectully, Wouter.
Thank you.
Wow 🤯 thank you! That’s very kind. Made my week 🙏🏻
Lucky to be ur first viewer!
I’m the lucky one ☝🏼 thanks for watching!
Thank you doctor 😘
You're welcome 😊
Thank you for the great video, it really helped me a lot, but one question, why there are no rephasing slice selection gradient when the 180 degree RF pulse is applied?
The 180 degree rf pulse is the rephasing mechanism.
Thank you for wonderful lecture..I have a one question ? First slice selection gradient are applied after 90 pulse or before 90 degree pulse
why do we not use a rephasing SSG for the 180 degree RF pulse and only for the initial 90 degree pulse?
Waited alot
Was out of town for a week so couldn’t film. Also making all these 3D models and animations from scratch. They will keep coming though, >120 videos filmed this year so far 🙂 hope you found it useful at least
In correspondence with the 180-degree pulse, I see another gradient. Does this mean that simultaneously with the 180-degree pulse, a gradient equal to the initial one is applied?
Thanks alot
Pleasure Merlo 🙂
Thank you for these amazing videos. Could you please clarify to me the difference between receiver bandwidth and transmit bandwidth? Because I have read in some books that they have different action on the SNR. I'm confused
Pleasure! The term bandwidth means range of frequencies. Transmit bandwidth refers to the range of frequencies that make up the radiofrequency pulse - the larger the transmit bandwidth the thicker the slice selected and therefore higher signal to noise.
Receiver bandwidth refers the the range of frequencies across the frequency encoding direction of a slice (it is completely separate process to transmit bandwidth). I cover this concept more in the bandwidth talk of this series - hopefully that video will help 👍🏼
Hi professor！Your video was truly fantastic; your explanation was very clear. I'm really grateful. I have a question I'd like to ask you: since in TE (echo time) the protons in the slice are precessing in phase, making it impossible to determine the exact location of the signal within the slice, why do we need the rephasing gradient step? Wouldn't it be possible to know where the signal is coming from at TE without rephasing? Is the purpose of rephasing to ensure that all the protons in the entire slice precess in phase? If so, what is the objective of doing this?
Hi! Great question. At the end of the RF pulse the protons are in phase, at TE the protons are rapidly dephasing due to T2* decay. They are also dephasing because the gradient we apply in the x direction (frequency encoding gradient) causes spins to precess at different frequencies. These different frequencies allow us to localise signal but we lose transverse signal even quicker as a result of the gradient field. The rephasing gradient allows us to recover some of this lost signal. I go over this in depth during the gradient echo talk (part 1). Check that video out and it should make more sense 🙂
Thank you so much! I'll check out the gradient echo video. Again, I love your tutorial videos! I really appreciate your efforts@@radiologytutorials
Why there is no rephasing pulse after 180 degree pulse
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Stupid question, so to adjust the T2 contrast we adjust the TE time, does that mean we adjust when 180pulse is applied since it must be half way between 90 pulse and TE?
Great question. Exactly, if it's a spin echo sequence the 180 degree pulse must be moved in proportion to the change in TE.
@@radiologytutorials thank you so much!
Feels like my tuition fee should hand it to you instead of my uni
😂 love this!
So there will be no table movement in MRI like in CT as a whole...gradient coils will take up the work and plotting signal in K space and acquire the data. Am I right sir??
Good thought. There is table movement in MRI. In theory we could do all the slice selection with the gradient coil and RF pulses. However, the main magnetic field is the most homogenous in the centre of the scanner. Therefore, we will often move the patient (like we do in CT) to ensure the slice we are imaging is near the centre of the magnet.
@@radiologytutorials okay sir...Thank you for your kind reply ☺
Any time. Feel free to ask anything 🙂
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