 - MRI and MRS scan of the head: These tests use a magnetic field and radio waves to obtain images of the brain and detect changes in certain brain chemicals that may be affected by HIV infection. Both procedures are done at the same time. The patient lies on a table that is moved into the scanner a narrow cylinder, wearing earplugs to muffle loud knocking and thumping sounds that occur during the scanning process. The procedure lasts about 50 to 60 minutes, during which time the patient can communicate with the staff. 