MRI: A Guided Tour

Shades of Gray

Here’s a picture (sagittal view) of your spine! Now it’s clear what the trouble is. See the dark disc that, unlike the others, protrudes into the spinal canal? That’s a herniated disc compressing the nerves of the spinal cord. Ouch!

Herniated disc.

Believe it or not, MRI scans can display more than 250 distinct shades of grey, each reflecting slight variations in tissue density or water content. It is in those subtle shades that radiologists unlock the secrets of the tissues. For example, abnormal tissue, such as a brain tumor, will look different than the normal tissue surrounding it. The technologist and radiologist have the ability to alter imaging parameters (like the timings of the RF pulse and gradients) to emphasize areas of injury or disease or to acquire higher image resolutions.

Now that your scan is over, you’re free to move around – do jumping jacks, dance a jig, celebrate your liberation. Unstop your ears, trade in the hospital gown for your street duds, reclaim your jewelry and watch. The MRI has not changed anything about your body or its chemistry. In fact, unlike X-rays or CT scans, you can have as many MRI scans as often as is necessary to diagnose your ailment and track your recovery after treatment.

We hope that the bad news about your back has been tempered by a newfound appreciation for the beauties of science and the wonders of technology. If we’ve whetted your appetite for more information on the topic, you might visit some of the Web sites listed on the next page.

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Thanks to the Magnet Academy's scientific adviser on this article Sam Grant, an assistant professor of engineering with the Florida A&M University/Florida State University College of Engineering and an expert in MRI at the Magnet Lab.