Final answer:
The three dimensions critical to understanding MRI are the position of each galaxy on the sky (two dimensions) and the distance of each galaxy from us (the third dimension).
Step-by-step explanation:
The three dimensions that are critical to understand Magnetic Resonance Imaging (MRI) are:
- Position of each galaxy on the sky (two dimensions)
- Distance of each galaxy from us (the third dimension)
These three dimensions are important because they allow us to map large parts of the universe in three dimensions, which in turn helps in understanding the distribution and structure of galaxies.