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Special Diagnostic Tests
Bone Density Testing, CT Scans, and MRI
Many tests are available to help doctors care for you. Knowing more about the different kinds of tests can help you understand why they are needed. Bone density testing, CT scans and MRI tests are three important testing tools. Here, you can find out what to expect and why they are used.
Bone density testing
What is a bone density test?
A bone density test is just what you might guess – a type of x-ray that measures the density (strength) of your bones.
When is it used?
This test is usually used to diagnose osteoporosis, a condition where bones are thinner (less dense) than expected. Osteopenia is a related condition – it is osteoporosis in a milder form. Thin or brittle bones do not usually cause any warning symptoms like pain or discomfort. However, people with brittle bones are at much greater risk of a fracture (broken bone) if they fall or are injured. A bone density test can measure how strong your bones are, so that you and your doctor will know if you must strengthen your bones to prevent fractures. The test is also used for people with osteoporosis to monitor whether treatment is helping.
Are there any risks?
The test is painless and very safe. As with any x-rays, your body is exposed to a small amount of radiation. In large amounts, radiation can increase the risk of cancer or birth defects. However, the amount of radiation in a single bone density test is extremely small and very unlikely to cause any problems. If you are pregnant or think you might be, it is important to inform the technologist.
What should I expect during a bone density test?
On the day of the test, no special preparation is needed. It is best to wear a two-piece outfit that has no metal parts, such as zippers or snaps, since metal on your clothing may interfere with the test. You probably will not need to change into a hospital gown if you wear this type of clothing.
Most people find the test to be quite simple. When you arrive, a bone density technologist will greet you and may ask questions about your medications and medical history.
You will be asked to lie down on an examination bed. Usually, the test measures the bone density of your spine and hip. To examine your spine, you may be asked to lie on your back with your legs elevated so that the small of your back lies flat on the bed. To examine your hip, your leg will be carefully positioned, turned slightly outwards.
A moving arm that hangs over the bed detects x-rays that are passed through your bones. During the test, the machine may make a few soft clicking and whirring noises. The technologist will be in the room to answer questions or address your concerns. The test takes about 10 to 20 minutes.
Who cannot have a bone density test?
Since the machine makes very precise measurements, you must remain still during the test. If you cannot lie on your back for 10 to 20 minutes, or stay still (because of tremors, for example), you may not be able to complete the bone density test. If both hips have been replaced, the test will not be able to measure the bone density of the hip. In the same way, if you have had certain surgeries on your back, it may be difficult to accurately measure the density of your spine.
Should everyone have a bone density test?
No. Your doctor is the best person to decide if a bone density test is useful for you. If you are concerned about your bone density, discuss this with your doctor.
CT scan
What is a CT scan?
A CT scan, or CAT scan as it is often called, is a special type of x-ray test. CT stands for computed tomography. During a CT scan, x-rays are taken from a number of different angles. These images are then arranged by a computer to create a cross-section view of the body.
When is a CT scan used?
A CT scan is used when your doctor needs a more detailed picture than a regular x-ray provides. Some structures, such as bones, are easy to see on a regular x-ray. However, organs like the liver or the brain do not show up well on a regular x-ray. A CT scan is very useful for getting information about these parts of the body.
Are there any risks?
You are exposed to a larger amount of radiation with a CT scan than with a bone density test. A single test is unlikely to cause any problems.
Sometimes, a contrast agent is used to get a clearer picture of certain organs or body part being studied. If you take the medication metformin, the agent can affect your kidneys and how your body clears this drug from your system. If this is true for you, you must follow special instructions. Discuss this with your doctor before testing.
What should I expect during a CT scan?
Depending on the part of your body being scanned, you may need to remove metal objects such as jewelry and change into a hospital gown. Before the test, you may be given a contrast agent, either to swallow or through an injection. You will lie down on a table, usually on your back. The scanner is a large, doughnut-shaped machine that can take x-rays from different angles. The machine may make some noise and the table may move slightly during the test. This is normal.
MRI
What is an MRI test?
MRI stands for Magnetic Resonance Imaging. Unlike a CT scan, an MRI test does not use radiation. Strong magnetic fields and computer processing are used to create the images.
The MRI test is a bit more complicated to understand than x-rays or CT scans. Basically, all the molecules of the body contain atoms. The central part of the atom is the nucleus. The nucleus has a north and a south pole, like a regular magnet. Normally, the nucleus is in a random position. When exposed to a strong magnetic field, it will put itself in line with the magnetic field.
In an MRI examination, a large magnetic coil is placed around you. It creates a pulse of magnetic energy. The nuclei (plural of nucleus) of your body line up with the magnetic field. When the pulse is turned off, the nuclei return to their random positions. In doing so, they give off a signal. The computer picks up the signals and is able to turn them into images.
When is an MRI used?
While x-rays and CT scans are very good at showing bones, an MRI gives clear, detailed images of structures made of soft tissue, such as ligaments and cartilage, and organs like the brain and the eyes.
Are there any risks?
There are no known harmful side effects. You will not feel any pain or discomfort during the MRI test. However, as it uses a powerful magnetic field, it is extremely important that no magnetic materials enter the examination room. Any magnetic material would be instantly and forcefully drawn to the magnetic coil. If you entered the exam room with a screwdriver, it would actually fly out of your hand towards the powerful magnet! Metal put into the body during surgery, such as a metal plate that holds a broken bone together, is not magnetic and is safe.
If you and your doctor are worried that you may have another type of metal in your body, a plain x-ray can find this out. For instance, have an x-ray of your eyes done if you weld or have worked in a machine shop. You may have small shards of metal lodged in your eyes.
What should I expect during an MRI?
When you come in for the examination, you will be asked to fill out an MRI safety form. This checks for any risks before you enter the magnetic field. Wear as little jewelry as possible.
During the examination, you will be lying on a table within the tunnel of the MRI machine. The machine makes loud, knocking noises during the test.
However, headphones or earplugs are provided, and usually you can listen to your favorite music CD if you bring it along. People who are afraid of enclosed spaces may be uncomfortable lying within the tunnel. If this is the case, ask your doctor for a mild oral sedative to take before the examination.
Although you will be alone in the exam room, a technologist can see you, hear you, and talk to you at all times. You will have an emergency call button in case you need to contact the technologist during the procedure. Most MRI tests take from 30 to 60 minutes.
Following these examinations, a written report will be sent to your doctor within a few days. You can make an appointment with your family doctor to discuss the results of your test.
FAMILY HEALTH is written with the assistance of |
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FAMILY HEALTH is written with the assistance of |
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