INFORMATION ON X-RAYS, MRI, CT (CAT) SCANS AND BONE SCANS
Following below is some information on the more common ways that exist to look inside your feet to see the tissues deep inside. Topics discussed are:
How do X-Rays work?
An X-ray machine is basically a camera. But instead of using visible light waves, it uses X-Rays to expose the film.
You see, visible light, X-Rays, Television waves, radio waves, microwaves, cell phone waves are all basically the same; they are electromagnetic waves. The only differences are the amount of energy each possesses--which causes them to travel in different wavelengths.
X-rays are more energetic than light, so they can penetrate many materials (like skin, muscle and tendons) much better than light, so it passes through these tissues to expose the film beneath the body. This is why X-rays look black to grey in areas where there is soft tissue.
But X-rays have a harder time penetrating bone. An X-ray encountering a bone is mostly absorbed by that bone, causing less of the the X-ray to hit the film. This is why an X-ray in an area of bone looks relatively more white than the surrounding tissues.
Thus, the image you see on an X-ray is created because different levels of exposure have reached the film after passing through parts of the body tissues of different densities.
A bone scan is an imaging procedure which involves injecting the patient with a small amount of a special imaging tracer. There are several types of tracer materials, but the most common type of bone scan, the the most common is a Technetium Scan, which uses a tracer called technetium. In this case, the Technetium is attached to a calcium-like material and injected into the body. This tracer is visible on film taken by a special type of camera that only sees that tracer material.
Bone scans are very sensitive--meaning even slight changes from normal are picked up by the camera. But bone scans can't differentiate between the various causes of bone activity. Thus, they can tell you that something is, in fact, wrong with the bone, but the can't tell you what is wrong with the bone.
A technetium bone scan is a common test, and what most people are referring to when they talk about bone scans. Still, there are other types of bone scans available:
A Ceretec scan uses the same tracer, technetium, as a traditional technetium bone scan, but instead of attaching it to calcium-like material to follow bone activity, the tracer is attached to white blood cells, the cells that help you fight off infection. When injected back into the body, the labeled white blood cells migrate towards any infection that may be present. If they accumulate in some location, this test may help us determine where an infection may be present. This test is an excellent imaging test to assess for osteomyelitis (bone infection).
Indium scans, too, are used to monitor signs of infection of bone. With this test, a tracer known as Indium is used to label the same white blood cells used with a ceretec scan.
Another test used more rarely is the Gallium scan, which uses a Gallium tracer. It uses the same type of technology as the above scans, but this test is used to assess for infection, inflammation or possibly tumours. This test is used more rarely in podiatric medicine than the other types of bone scans mentioned above.
CT (CAT) Scans
Computerized tomography, or CT scan, also known as a Computerized Axial Tomography or CAT scan is a specialized form of X-ray. The special X-ray beam rotates around the body taking pictures, and a computer takes the data and recombines it to form cross-sectional images of the body.
MRI is an imaging technique developed in the
1980's. MRI stands for Magnetic Resonance Imaging, an technique that
uses radio waves, a powerful electromagnet and a computer to view the soft
tissue of the body. Unlike X-rays or CT, MRI does not
expose the body to radiation.
And because the computer can create another image a quarter inch to the left or right, we can really zoom in on the tissue of concern.
As a general rule, MRI is better than CT to view soft tissues, whereas CT is particularly good to look at bone--although there is some overlap.
As magnets are used in taking an MRI, patients with metal implants--a pacemaker, stent, metallic pins or screws, for example--may not be able to use this technology.