I need one clarification. I understand fully the flow related enhancement effect for incoming "fresh spins" which are excited with a maximum longitudinal magnetization . But isnt it true that on the subsequent 90 degree excitations some of the latter out flowing spins will also contribute to this flow related enhancement and like said in previous videos their signal will still be spatially localized correctly assuming the flow is perpendicular to slice? Therefore I assume there must be a "magic TR" which is a function of slice thickness and flow velocity for which the flow related enchancement is maximised. Very short TR means the steady state signal from outflowing spins will be low whereas for very long TR the spins have flown far away from the receiver.....Therefore this magic TR value must be somewhere in the middle of these extremes.
@25:50 Contrast enhancend TOF is actually used - with the idea of increasing signal for areas of slow flow, which are problematic in normal TOF, as well as against the overestimation of stenoses; although I would be thankful if anyone could explain the reason for how this is beneficial?
hello! thank you very much for sharing this video! regarding 2d e 3d technique: basically in terms of slice thickness what is the difference? i mean.. how much thick could a 2d slice be and a how much thin could a 3d "slab" be? when does a slice finish to be a "slice" and start to be a "volume"????
I had watched all the videos from the first until this but i don’t know in wich you explained about dephasing at 2,3 4,6 and 6,9 , I missed something? I now that there is a difference in the frequency of precession between fat and water and other tissus but I don’t understand how do you know that we need Exactly TE at 6,9 ?
Rajae STIHA chemical shift between water and fat il around 220 Hz at 1.5T, which means fat and water precessions have different speed which is 1 second divide for 220 cicles per second (Hz), that makes around 4,5 ms. Every integer cycle (so every 4,5 ms) you get water and fat in phase, every half of cycle (so 2,25 - 6,9 - ...) you get them out of phase
Or just learn some proper English like most foreigners do for their study. If u expect to understand this complicated level of physics and medicine, English is peanuts anyway :)
The best explanation of the TOF and the work of Saturation Bands! Thank you Dr. Lipton!
How is both time of flight effect and high velocity signal loss occurring in spin echo imaging
I need one clarification. I understand fully the flow related enhancement effect for incoming "fresh spins" which are excited with a maximum longitudinal magnetization . But isnt it true that on the subsequent 90 degree excitations some of the latter out flowing spins will also contribute to this flow related enhancement and like said in previous videos their signal will still be spatially localized correctly assuming the flow is perpendicular to slice?
Therefore I assume there must be a "magic TR" which is a function of slice thickness and flow velocity for which the flow related enchancement is maximised. Very short TR means the steady state signal from outflowing spins will be low whereas for very long TR the spins have flown far away from the receiver.....Therefore this magic TR value must be somewhere in the middle of these extremes.
@25:50 Contrast enhancend TOF is actually used - with the idea of increasing signal for areas of slow flow, which are problematic in normal TOF, as well as against the overestimation of stenoses; although I would be thankful if anyone could explain the reason for how this is beneficial?
Nicely explained! Thanks!
hello! thank you very much for sharing this video!
regarding 2d e 3d technique: basically in terms of slice thickness what is the difference?
i mean.. how much thick could a 2d slice be and a how much thin could a 3d "slab" be?
when does a slice finish to be a "slice" and start to be a "volume"????
I had watched all the videos from the first until this but i don’t know in wich you explained about dephasing at 2,3 4,6 and 6,9 , I missed something? I now that there is a difference in the frequency of precession between fat and water and other tissus but I don’t understand how do you know that we need Exactly TE at 6,9 ?
Rajae STIHA chemical shift between water and fat il around 220 Hz at 1.5T, which means fat and water precessions have different speed which is 1 second divide for 220 cicles per second (Hz), that makes around 4,5 ms. Every integer cycle (so every 4,5 ms) you get water and fat in phase, every half of cycle (so 2,25 - 6,9 - ...) you get them out of phase
Math. The difference between fat and water precession is around 3.5 parts per million. You can insert any number you want to as an example
please, add spanish traslate, please :) very nice video
Or just learn some proper English like most foreigners do for their study.
If u expect to understand this complicated level of physics and medicine,
English is peanuts anyway :)