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Types of Diagnostic Testing
What is a Bone Scan?
What is a MRI?
What is an EMG/NCV (Nerve) test?
What is a CT Scan?
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What is a Bone Scan?
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Your doctor may order a bone scan to help diagnose subtle
or hidden bone fractures that may not show up on a routine X-ray, such as a
stress fracture. Bone scans can also help detect:
- Bone cancer
- Bone infections
- Arthritis
- Causes of unexplained bone pain
No special preparation is required on your part before a
bone scan, though you may be asked to remove jewelry or other metal objects. You
can eat or drink anything you like before the test.
As with most tests, tell your doctor if you're pregnant or
think you might be pregnant. Bone scans aren't performed on pregnant women
because of concerns about radiation exposure to the fetus.
A bone scan can be divided into two basic parts:
- The injection. You will
receive an injection of tracers into a vein in your arm. You'll then wait
about two to four hours to allow the tracers to circulate and be absorbed by
your bones. You may be allowed to leave the health care facility while you're
waiting. Your doctor will ask you to drink several glasses of water so you'll
urinate frequently — this removes unabsorbed radioactive material from your
system.
- The scan. During the scan,
you'll be asked to lie very still on a table while a machine with an arm-like
device supporting the gamma camera passes over your body and records the
pattern of tracer absorption in your bones. This is painless. A scan of your
entire skeleton takes about 30 minutes. Scanning a limited area of your body
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What is a MRI?
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These images especially are helpful for examination of
the brain, neck, spinal cord and soft tissues. MRI often is used in the
diagnosis of central nervous system disorders, such as multiple sclerosis,
because of its high-resolution images of the brain and spinal cord's white and
gray matter. In addition, MRI can be helpful for evaluating joint, ligament,
muscle and bone problems.
You can eat normally and continue
to take your usual medications before this procedure, unless otherwise
instructed. You may be asked to remove your street clothes and given a gown and
robe to wear or told to wear clothing without metal fasteners, such as sweats.
Before the test, you will need to remove all accessories — watch, jewelry,
hairpins. Also remove wigs, dentures and hearing aids. This is necessary so that
metallic objects in these items won't affect the quality of the MRI picture and
to prevent electronic items — watch, hearing aid — from being damaged by the
magnets.
Tell the technologist if you have
any metal or electronic devices in your body, such as metallic joint prostheses,
artificial heart valves, implanted electronic devices, cochlear implants or
magnets in your dentures. The presence of metal in your body may be a safety
hazard or affect a portion of the MRI image.
You shouldn't receive an MRI scan
if you have an implantable cardiac defibrillator or pacemaker. The strong
magnetic field produced by the MRI unit may interfere with the pacemaker's
function.
If you think you're pregnant,
tell the technologist before undergoing MRI imaging because the effects of
magnetic fields on fetuses aren't well established.
If you have any questions, ask
your physician or MRI technologist.
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The MRI machine is a large magnet
with a central opening. You'll lie down on a moveable table that slides into the
opening of the magnet. Depending on the part of your body to be examined, a
small coil may be placed around that portion being examined to receive the MRI
signal.
A technologist will monitor you
from another room, and you will be able to talk with the technologist by
microphone. In addition, you may be allowed to have a friend or family member
stay in the room with you.
The MRI machine creates a strong
magnetic field around you, and radio waves are directed at your body. You will
not feel the magnetic field or radio waves, and there are no moving parts around
you.
You will hear repetitive tapping,
thumping sounds or other noises during the MRI scan. These sounds come from the
internal part of the magnet. Ear-plugs or music may be provided to help block
the noise.
An MRI examination can take
between 30 and 90 minutes. While the scan is taking place, breathe quietly but
comfortably, without moving your head or body. Most people find that after
several minutes of imaging they become quite relaxed and have few problems lying
still for the duration of the examination. If you have a hard time lying still
for the required period of time or are anxious about the enclosed space, you may
be given a sedative. Some MRI units may be wider, shorter or open on all sides,
which may be more comfortable for you. However, the quality of images taken from
these systems may vary.
In some cases contrast agents are
injected into your veins to enhance certain tissues or blood vessels in the
images. These will be inserted into an arm or hand vein with the use of a needle
connected to an intravenous line. These contrast agents are different than those
used in kidney tests or computerized tomography (CT) scanning. They don't
contain iodine and are less likely to cause an allergic reaction.
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What is an EMG/NCV (Nerve) test?
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Electromyography is a test that measures muscle response
to nervous stimulation (electrical activity within muscle fibers).
How the test is performed
For an EMG, a needle electrode is inserted through the
skin into the muscle. The electrical activity detected by this electrode is
displayed on an oscilloscope (and may be displayed audibly through a speaker).
Because skeletal muscles are isolated and often large
units, each electrode gives only an average picture of the activity of the
selected muscle. Several electrodes may need to be placed at various locations
to obtain an accurate study.
After placement of the electrode(s), you may be asked to
contract the muscle (for example, by bending your arm). The presence, size, and
shape of the wave form -- the action potential -- produced on the oscilloscope
provide information about the ability of the muscle to respond when the nerves
are stimulated.
Each muscle fiber that contracts will produce an action
potential, and the size of the muscle fiber affects the rate (frequency) and
size (amplitude) of the action potentials. A nerve conduction velocity test is
often done at the same time as an EMG.
Nerve conduction velocity (NCV) is a test of the speed of
conduction of impulses through a nerve.
How the test is performed
The nerve is stimulated, usually with surface electrodes,
which are patch-like electrodes (similar to those used for ECG) placed on
the skin over the nerve at various locations. One electrode stimulates the nerve
with a very mild electrical impulse.
The resulting electrical activity is recorded by the other
electrodes. The distance between electrodes and the time it takes for electrical
impulses to travel between electrodes are used to calculate the nerve conduction
velocity.
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What is a CT Scan?
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CAT scan; Computed axial tomography (CAT) scan
Definition
Computed tomography (CT) a method of body imaging in which
a thin x-ray beam rotates around the patient. Small detectors measure the amount
of x-rays that make it through the patient or particular area of interest.
A computer analyzes the data to construct a
cross-sectional image. These images can be stored, viewed on a monitor, or
printed on film. In addition, three-dimensional models of organs can be created
by stacking the individual images, or "slices."
How the test is performed
The patient will be asked to lie on a narrow table
(gantry) that slides into the center of the scanner. Depending on the study
being performed, the patient may need to lie on his/her stomach, back, or side.
If contrast media (dye) is to be administered, an IV will be placed in a small
vein of a hand or arm.
Much like standard photographic cameras, subject motion
causes blurred images in CT. Therefore, the technologist operating the scanner
and supervising the patient will give instructions through an intercom when to
hold one's breath and not move.
As the exam takes place, the gantry will advance small
intervals through the scanner. Modern "spiral" scanners can perform the
examination in one continuous motion of the gantry. Generally, complete scans
will only take a few minutes, however, additional contrast-enhanced or
higher-resolution scans will add to the scan time. The newest multidetector
scanners can image the entire body, head to toe, in less than 30 seconds.
How to prepare for the test
The CT scanner has a weight limit to prevent damage to the
mechanized gantry. Have the health care provider contact the scanner operator if
you weigh more than 300 pounds.
Since metal is very, very dense, the x-ray beam has
difficulty passing through it and results in errors in the involved constructed
slices (artifact). Therefore, the patient will be asked to remove jewelry and
wear a hospital gown during the study.
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