The website e-mri.org used to have excellent interactive online demonstrations of basic concepts regarding spin states, sequences, and k-space, but it doesn't seem to be available anymore. I did save quite a few screen captures and included them in a lecture I gave a year ago in case anyone is interested:

http://www.mindboggle.info/lectures/PETc...

It also includes information from the website: http://www.cis.rit.edu/htbooks/mri/insid...

Cheers,
@rno

--
arno klein
arno@binarybottle.com
asst. professor of clinical neurobiology
columbia university