How radiology works - an extensive collection of articles and online videos about the physics and mathematics of x-ray imaging. Recommended!

https://howradiologyworks.com/

https://www.youtube.com/channel/UC3MTvd6kJizu7S_2-lyPXuA

An Interactive Guide To The Fourier Transform
https://betterexplained.com/articles/an-interactive-guide-to-the-fourier-transform/

Nuclear physics for medicine
http://www.nupecc.org/npmed/npmed2014.pdf

The Fourier Transform and its Applications
https://see.stanford.edu/materials/lsoftaee261/book-fall-07.pdf