MRI machines resemble long, narrow tubes that have both ends open. You lie down on a movable table that slides into the tube's opening and by using a microphone, you can communicate with them. Radio waves are directed at your body by the MRI machine, which creates a strong magnetic field around you. There are no moving parts around you, and you can't feel the magnetic field or radio waves. The internal part of the magnet produces repetitive tapping, thumping, and other noises during the MRI scan. If you want to block out the noise, you might be given earplugs or have music playing.   Contrast material, usually gadolinium, may be injected through an intravenous (IV) line into a vein in your hand or arm; certain details are enhanced by the use of this contrast material. There are very few allergic reactions associated with gadolinium. The duration of an MRI can range from 15 minutes to more than an hour. It is important to remain still when taking pictures since movement can blur them.   You may be asked to do a number of small tasks during a functional MRI, such as movements or answering simple questions. The attending physician can pinpoint which parts of your brain control these actions this way. The MRI results will typically be made available to patients within one to two weeks.