MRI safety

Unlike other imaging forms like X-rays or CT scans, MRI doesn't use ionizing radiation. MRI is increasingly being used to image fetuses during pregnancy, and no adverse effects on the fetus have been demonstrated, Filippi said.

Still, the procedure can have risks, and medical societies don't recommend using MRI as the first stage of diagnosis.

Because MRI uses strong magnets, any kind of metal implant, such as a pacemaker, artificial joints, artificial heart valves, cochlear implants or metal plates, screws or rods, pose a hazard. The implant can move or heat up in the magnetic field. 

Several patients with pacemakers who underwent MRI scans have died, patients should always be asked about any implants before getting scanned. Many implants today are "MR-safe," however, Filippi said.

The constant flipping of magnetic fields can produce loud clicking or beeping noises, so ear protection is necessary during the scan.

Functional MRI

In addition to structural imaging, MRI can also be used to visualize functional activity in the brain. Functional MRI, or fMRI, measures changes in blood flow to different parts of the brain. 

It is used to observe brain structures and to determine which parts of the brain are handling critical functions. Functional MRI may also be used to evaluate damage from a head injury or Alzheimer's disease. fMRI has been especially useful in neuroscience — "It has really revolutionized how we study the brain," Filippi told Live Science.

Diffusion MRI

This form of MRI measures how water molecules diffuse through body tissues. Certain disease processes — such as a stroke or tumor — can restrict this diffusion, so this method is often used to diagnose them, Filippi said. Diffusion MRI has only been around for about 15 to 20 years, he added.