Can mri evaluate thickness of the fascia perfectly in an individual?can it also detect weakness?

Nothing : In medicine is perfect. Mri is good at looking for fascial thickness, edema, and tears however.

Imperfect: Mri can look for inflammation and tears. Weakness is a sensation felt by the person, people react to injury differently, so this cannot be judged on mri. There is no set "normal" for fascial thickness. It varies in each person as well. However, one can look at the normal portion to assess if another area is too thick or thin for that person.