Introducing MRI: Spatial Localization and k-space: Review and Q&A (25 of 56)

www.einstein.yu.edu - The twenty-fifth chapter of Dr. Michael Lipton's MRI course covers Spatial Localization and k-space: Review and Q&A. Dr. Lipton is associate professor radiology at Albert Einstein College of Medicine and associate director of its Gruss Magnetic Resonance Research Center.

[@akhileshdixit1091]

best study material and way of presentation

[@dharmendrabaghel]

Great lecture! I come from the computer science background still having fun learning MRI.

[@thin009]

Really Great Lecture!
But I do have one question: The measured signal which contains out of several different frequencies looks like a sine function with an decreasing amplitude (which makes sense). But in the last lecture (Number 23 and 24) the signal was just an exponential decay which rises again after the 180 degree pulse and the measurment of this Echo leads to the symmetric matrix in the k-space. But with the decaying sine signal in this lecture I dont understand how we get an symmetric matrix in the k space (for example because it would have negative values aswell).
So my question is: The combination of the sine waves with different frequencies form a new sine wave and we only detect/calculate the envelope of the signal and write it in the k-space matrix? (But then the fouriertransformation wouldnt lead the right frequencies)

[@turdferguson3400]

Please fix the order of the lecture series in the playlist. It jumped from lecture 9 to lecture 25.

[@tuhinchakraborty1790]

Good lecture...i have one question why we apply multiple phase encoding gradient??? Instead.we can apply two different phase gradient that can also gives phase change...

[@rfmonkey4942]

sounds like a bulk sampling device is in order "lika an SDR" so exiting to even think about

[@eglen7664]

the level of explanation is awesome, thank you so much!

[@tameembhat415]

Thank you for such a nice lecture. I have one simple question... When you apply a frequency encoding gradient why there is no phase shift though i think it is there when protons precess at different frequency

[@lalithsharan4734]

You are right, there is a phase shift introduced. However, this can be rectified in the pulse sequence, where you generally apply a dephasing gradient shortly after you introduce a gradient field.

[@peterphan8991]

May I ask where is the first lecture?

[@kerekesreka8091]

Does the multiple sampling of the one signal mean that it equals as many TE?

[@EinsteinCollegeofMed]

Kerekes Reka Hi, can you please clarify your question, perhaps adding some detail so that Dr. Lipton can review it?

[@kerekesreka8091]

***** How long does the sampling go on under one TE? When does the sampling begin and when does it end? In some courses the prof. draws the FID as long as the whole process (beginning from the RF pulse and ending at the TE with the G of frequency).

[@Soroush592]

+Kerekes Reka TE corresponds to the time point at which we do our measurement after each repetition (at the end of TR). So when you say TE=10 ms, it means we will do our measurement 10 ms after the application of 90 RF pulse. This does not mean that we measure in all of this 10 ms. However, the measurement is not done in a single instant, as it is physically impossible, rather it is done over a time window around TE (say TE-1.5 to TE+1.5 ms) and that is where we record our signal.

[@daviddavies7871]

@@EinsteinCollegeofMed years later lol. I'm confused in that I thought each line of k space was sampled from 1 TE/TR period, but here you're saying that every line of k space from a whole slice is sampled from 1 TE/TR?

[@takeoverusa]

Shady but that’s Medicine