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So we've been discussing this in the classroom and I really can't say if my answer to this question is correct since there could be various answers to this.

I know that to have a high-resolution image, we have to move to higher frequencies and lower wavelengths. But the way MRI works is in contradiction to what I mentioned above since MRI uses RF which is high in wavelength and low in terms of frequency, however, it has high spatial resolution and high contrast compared to what we would expect.

What explains that?

A non-physics major here.

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  • $\begingroup$ I know that to have a high-resolution image, we have to move to higher frequencies and lower wavelengths. Is this always true? $\endgroup$
    – Daddy Kropotkin
    Commented Mar 16, 2021 at 15:22
  • $\begingroup$ Logically speaking, it seems reasonable to say that yet it seems that there are other factors like SNR, CNR, FOV, B0 and B1 fields involved. I'm baffled to be honest. Been looking for a solution, but I failed. $\endgroup$
    – user668687
    Commented Mar 16, 2021 at 15:41
  • $\begingroup$ If you could provide some references and tell us where you get this info from, it'll be easier for people here to help (make sure you include this in the question above). $\endgroup$
    – Daddy Kropotkin
    Commented Mar 16, 2021 at 21:59

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Image formation in MRI is fundamentally different from other imaging methods such as optical microscopy, x-ray imaging, or RADAR, where image resolution is determined in part by the wavelength of light used.

In MRI, you're detecting the resonant RF coming from the target atom or molecule (with conventional MRI used for medical imaging, it's usually hydrogen). Gradient magnetic fields applied to the sample/imaging volume cause a position dependent variation in the frequency of the resonant RF signal. How the RF signal is detected and sampled to pick out the different frequencies (and therefore the location in space where the signals originated) determines the image resolution.

MRI image contrast, on the other hand depends on several factors. One of these is how long you wait between the excitation RF pulse and detecting the resonant RF signal emitted by the sample.

This is the imaging process in a very small nutshell. There is of course a lot more to it.

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  • $\begingroup$ Could you please provide some supplementary read like articles or any related to this? I would really appreciate that. (the more, the better I can get good at it) $\endgroup$
    – user668687
    Commented Apr 1, 2021 at 7:52
  • $\begingroup$ MRI isn't my specialty and most of the references I have are fairly technical and not easily digestible. A Google search for "MRI physics" should bring up plenty of stuff for you to go through though. $\endgroup$
    – imabug
    Commented Apr 8, 2021 at 12:22
  • $\begingroup$ Yeah I did find a few underlying reasons for that but they were not really technically acknowledged (I reckon they are mostly for general audience(I'm a biomedical engineering student though and been looking for some technical read)) $\endgroup$
    – user668687
    Commented Apr 10, 2021 at 5:57
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    $\begingroup$ Any textbook on medical imaging physics (Bushberg, Wolbarst, etc) will cover the essentials of MRI. AIP published a book a long time ago called "NMR in Biomedicine: The Physical Basis" that's a collection of the seminal papers in NMR and MRI. Might be something you can get through your library via ILL if they don't already have a copy. $\endgroup$
    – imabug
    Commented Apr 11, 2021 at 10:58
  • $\begingroup$ Thank you so much! That's a good idea to read these. $\endgroup$
    – user668687
    Commented Apr 12, 2021 at 14:51

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