During the diagnostic process, our doctors will sometimes send us to be examined using machines like X-Rays, CT Scans, Ultra Sound, MRIs and PET Scans. What are their differences and why does the doctor choose one instead of another?

The first X-Ray machine was invented in the late 1800s and is still one of the best diagnostic tools available. It is used for viewing skeletal systems, lungs, blood vessels or intestines. X-Rays are quick and painless and produce a negative photograph for the doctor to study.

A CT Scan, often pronounced "cat scan," uses computerized tomography. That means it combines X-Rays with mathematical algorithms to produce three-dimensional pictures of one’s spine, blood vessels, or muscles. CT Scans are also used to identify tumors. The scan itself is painless, and its duration depends on what is being studied.

If you’ve been pregnant then you’re familiar with Ultrasound. Sound waves are sent into the body, and changes in the reflection of the sound, called a Doppler effect, produce images which can be viewed on a monitor. Ultrasound is painless and very safe. Besides pregnancies, it is also used to track blood flow through veins and arteries.

Magnetic Resonance Imagining, MRI, makes use of a huge magnet combined with radio waves to examine the internal body and produce incredibly detailed images in either two or three dimensions. MRIs are very noisy, can take a long time, and cannot be used for anyone with metal inside his body, such as a pacemaker or a pinned bone. But they are the test machine of choice when the high level of detail is needed for a diagnosis.

In the past few years, positron emission tomography, PET Scans, have become available. They follow chemical changes in the body and are used to track some cancers, analyze several brain disorders, and detect problems in the heart and with blood flow. Patients are injected with a low dose radioactive substance which can be followed through the body by the scanner. They are painless, but are so new and expensive, they may not be covered by insurance.

It’s good to know which diagnostic machines are used for what purpose. If your doctor wants you to be tested with one, be sure she helps you understand why she has chosen that test and what she expects to learn from it.

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