This book is a quick read, and it breaks down in reeeeally simple terms the physics behind MRI. It is far from satisfyingly complete (it is after all 100 pages, filled with cartoon drawings and large text), but it is a great way to get started before reading more advanced material. While it may look a lot like a children's book, it contains truely relevant information, but mainly gives you a mental image that helps you cope with these atomic level concepts. No math involved.
The only negative aspect was the extremely poor editing. Many pictures did not include reference titles, even though they were cited in the text, sentences missed verbs, or had the wrong punctuation. It was a bit of a mess.
Also, it does not ultimately tell you everything that matters in fMRI.