Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) produces high resolution images of the inside of the body differently than any other form of imaging. It produces two-dimensional and three-dimensional images that can identify very specific types of tissues and answer specific medical questions. In addition to showing tissue abnormalities, it can also be used to view blood flow within the body.

MRI is most widely used for diagnosing or identifying tumors and masses, viewing torn ligaments or cartilage, diagnosing spine problems, diagnosing strokes, and diagnosing multiple sclerosis (MS).

How it Works

The MRI technology uses a powerful magnet that affects the protons or hydrogen atoms within the body and forces them to align to the magnetic field. Most of the protons will cancel each other out by aligning in opposite directions, but the ones that don’t can be manipulated by radio frequency (RF) pulses that are specific to hydrogen atoms. The pulses cause those protons to spin at a specific frequency and in a specific direction that is based on the type of tissue being viewed and the strength of the magnetic field. Additional low strength magnets called gradient magnets, begin working at this point and allow the MRI machine to narrowly target very small regions for viewing. These regions, which are essentially slices of the body, can be viewed from any angle. They can slice in any direction without having to move the body as you do in x-rays. The atoms return to their original position once the RF pulse is turned off, and in doing so release energy that is detected, amplified, and interpreted by a computer.

Normal tissue and abnormal tissues respond differently to the magnetic field of the MRI machine. This creates variations in the signals released by the body's hydrogen atoms, which in turn creates variations in the images produced. This allows radiologists to more easily determine what is normal and what is not normal.

What to Expect When You Have an MRI
The MRI machine is a large cube-shaped machine with a wide cylinder (tube where either your entire body enters, or just the part of the body that is to be imaged. While inside the tube you will be able to communicate with the nurses and technicians during the entire scan. While very few patients ever suffer claustrophobia during the procedures, medicines may be offered to relieve these symptoms, if necessary.

Screening
Because of the extremely powerful magnet that the machine uses, you will be screened prior to the exam to make sure you have no metal objects either on or within your body that might interfere. Metal within your body can be as big a problem as metal on the outside of your body, if it is magnetic. Typically, newer metal surgical implants pose no threat because they are made of nitinol or tungsten and are not magnetic. Shrapnel, metal shavings, or even some types of pins and clips inside your body may cause problems and could mean you will not be able to be scanned. Those items could potentially be bent or shifted by the magnetic field of the MRI machine.

People with pacemakers and aneurysm clips cannot be scanned because the magnet could make the pacemaker malfunction and could make the aneurysm clip shift and tear the artery it is attached to. Even the technicians must remove any metal objects from their clothing or bodies prior to entering the scan room because the strength of the magnet will pull the objects into the machine.

Landmarking
Once you have been screened and cleared for your scan, a technician will place an imaging coil around the area of your body to be scanned. The imaging coil is the part of the machine that applies the radio frequency pulses. They will then position you so that the part of your body to be scanned falls within a criss-crossed light beam. This is called landmarking.

The Scan
The scan will last anywhere from 20 minutes to an hour. The images are collected during time segments of 3 to 10 minutes. During this time you have to remain completely still (normal breathing is ok) so the images will not be distorted. Between these segments you may be able to move slightly, but you cannot change your position.

The MRI machine makes relatively loud noises as the scans are taking place. This is due to the gradient magnets turning on and off. It sounds like a series of short grinding bursts. You will be given earphones to wear and may listen to music during the exam.

Results
Once the scan is complete the radiologist will read and interpret the scan. Then your physician will share the results with you.