Magnetic resonance imaging uses sophisticated technology to image the inside of the brain and spine.  It has the ability to show images in three planes;  1)axial (the body is shown in slices across, like slicing a salami), 2) coronal (the slices are taken from side to side, like a crown extending over the head, from one ear to another), and 3) sagittal (from front to back, like the arrow shot by Sagittarius (therefore the name sagittal)).

While an MRI does not show bone anatomy as well as Computed Tomography (CT), it is excellent at showing soft tissue.  In particular, brain, spinal cord, and nerves are well seen.  A contrast agent known as gadolinium may be injected to show tumors, which often appear bright white on MRI.

There is no known adverse effects to a fetus, from MRI. 

Contrindications
(conditions for which MRI cannot be used) are:

• cardiac pacemaker, implanted neurostimulators, cochlear implants
• ferromagnetic aneurysm clips
• metallic implants or foreign bodies with large components of iron or cobalt
• metal fragments within the eye
• stents, coils or filters placed within the past 6 weeks

Relative contraindications:

• claustrophobic patients, although some may tolerate the procedure with sedation
• critically ill patients where monitoring during the procedure may be impaired
• obese patients:  size limitations may not permit the patient to fit within the closed bore MRI scanners;  an open MRI may be needed, although, depending upon the open scanner, image quality may suffer
• metal implants within the area of interest may impair good image quality