Functional MR imaging of the brain is a specialized MR study where the radio waves in a strong magnetic field are used to measure the quite and tiny metabolic changes that take place in an active part of the brain. Physicians know the general area of the brain where speech, sensation, memory and other functions occur. However the exact location varies from individual to individual. Injuries and diseases, such as stroke or brain tumor, can even cause function to shift to other parts of the brain. Functional MR imaging cannot only help the radiologist to look closely at the anatomy of the brain but can help them to determine precisely which part of the brain is handling critical functions such as thought, speech, motor activity, and sensation. This information can be critical when planning surgery or radiation therapy.