Is a week enough to view changes in mri or ct scan from water intoxication or what ? and how long period is enough to being detect in mri scan?

Nope, don't hurry...: Managing water intoxication is heavily based on the progressive evolving clinical pictures, and the tests such as mri, ; ct of skull/brain, which are, to an extent, optional. Generally, clinical pictures and electrolytes are all what we need; others are optional. Now, if you're slowly and surely getting better in electrolytes and mental alertness, it's absolutely no hurry to repeat.