Magnetic Resonance Imaging (MRI), once brain tumor symptoms of AN have been identified, is the most important diagnostic tool for acoustic neuroma. The use of this remarkable technology beginning in 1985 has significantly advanced early detection of even the smallest tumors, and MRI’s ability to produce a clear, three-dimensional image has greatly improved treatment planning as well. The MRI scan is a painless procedure lasting about 40 to 45 minutes. No radiation is involved in the procedure. A contrast agent (gadolinium) is administered intravenously so that the tumor will appear on the scan as a bright white (enhanced) area. For patients who may feel claustrophobic in the tunnel-shaped “closed” MRI machine, a mild sedative can be used. Less constrictive “open” MRI machines have been introduced, but are not recommended for the imaging of acoustic neuroma. Patients are warned that, because strong magnetic fields are generated, an MRI scan is not suitable for everyone, e.g., a patient with a cardiac pacemaker.