PET scans can also be expensive. Functional magnetic resonance imaging (fMRI) is a technique for measuring brain activity. It takes advantage of the fact that when neurons in a particular region are active, more blood is sent there. Advantages include that fMRI scans can resolve up to 3 cubic millimeters and are becoming even more powerful. One disadvantage is that any small movement can ruin the images. fMRI can map metabolic changes that indicate brain activity, to show an image with increasing precision, which parts of the brain are active while certain tasks are performed or while thoughts/emotions are processed. Magnetic resonance imaging (MRI) uses a strong magnetic field and radio waves to produce detailed images of the body's structures and organs. Advantages include that an MRI does not use radioactive material, therefore making it safe. An MRI can depict a slice of the brain taken from any angle and create a 3D image of the brain, and can produce more complicated information, allowing small tumors to be detected. The disadvantages of MRI are that any movement affects the image. Exposure to magnetism can be dangerous, brain function cannot be shown (only structure), no casual relationship can be determined, and it is also