Q: 1. What is an MRI?
2. I have a numbness from the ankle to the knee. What could be the reason?

A:1. MRI stands for Magnetic Resonance Imaging- a test to study the anatomy of any part of body. It is noninvasive, painless and is highly accurate though slightly expensive.
2. The problem described by you appears to be Peripheral Neuropathy a disease affecting nerves. Your best bet would be a nerve test called-NCV/EMG done by some Neurologist. However a prior neurological consultation is desirable.