Can an md diagnose dyslexia? Can MRI imaging diagnose dyslexia and if so how do I get my son tested

Some Developmental/ Behavioral Pediatricians test reading decoding & comprehension. Child psychologists, neuropsychologists & commercial programs like Lindamood-Bell do, also. Dr. Sally Shaywitz used functional MRI's to show that different parts of the brain are activated in readers vs. non-readers during reading tasks, but this is for research only. Read her book "Overcoming Dyslexia" for explanation.
Neuropsychologist. There are specially trained pediatric neuropsychologists who are phd level psychologists who are trained to diagnose specific learning disabilities including dyslexia. Your pediatrician my need to make the referral for testing. This is not a diagnosis done with an mri.
Sometimes, and no. A doctor may diagnose dyslexia if given a good description from the parents and a teacher. No x-ray or MRI diagnoses dyslexia. However, dyslexia should be diagnosed with testing by the child's school district (depends only on where he lives). This is required of all school districts in america. Then, parents can pay for another opinion from private testing clinics if parents want more information.