MRI is the method of choice in diagnostics (including early detection) of formations and focal changes in the brain substance and not only.
Research can be carried out depending on the results obtained during the first study. For example, on the first MRI of the brain, the conclusion: There were no data for the presence of pathological focal changes. Accordingly, the next MRI can be performed in 1 year (there is no harm from MRI at all), if there are any changes, the doctor himself will determine the timing of the next MRI. Also, the timing of the MRI depends on the patient's complaints.
In order to decide whether you need to do an MRI and how often, you need to consult a doctor (neurologist, therapist, etc.).
Yes, regular MRI will help identify a small tumor that has not yet manifested itself and timely diagnose its malignancy. You can also take an immunological profile for the detection of autoantibodies to proteins of the nervous tissue, if there is an increase in these autoantibodies in dynamics, then it is worth doing an MRI.