What is MRI
of the Body?
Magnetic resonance imaging (MRI) uses radiofrequency
waves and a strong magnetic field rather than x-rays
to provide remarkably clear and detailed pictures of
internal organs and tissues. The technique has proven
very valuable for the diagnosis of a broad range of
pathologic conditions in all parts of the body, including
cancer, heart and vascular disease, stroke, and joint
and musculoskeletal disorders. MRI requires specialized
equipment and expertise and allows evaluation of some
body structures that may not be as visible with other
imaging methods.
What are some common
uses of the MRI procedure?
Because MRI can give such clear pictures of soft-tissue
structures near and around bones, it is the most sensitive
exam for spinal and joint problems. MRI is widely used
to diagnose sports-related injuries, especially those
affecting the knee, shoulder, hip, elbow, and wrist. The
images allow the physician to see even very small tears
and injuries to ligaments and muscles.
In addition, MRI of the heart, aorta,
coronary arteries, and blood vessels is a fast, noninvasive
tool for diagnosing coronary artery disease and heart
problems. Physicians can examine the size and thickness
of the chambers of the heart, and determine the extent
of damage caused by a heart attack or progressive heart
disease.
Organs of the chest and abdomen—including
the lungs, liver, kidney, spleen, pancreas, and abdominal
vessels—can also be examined in high detail with
MRI, enabling the diagnosis and evaluation of tumors and
functional disorders. MRI is growing in popularity as
an alternative to traditional x-ray mammography in the
early diagnosis of breast cancer. Because no radiation
exposure is involved, MRI is often the preferred diagnostic
tool for examination of the male and female reproductive
systems, pelvis and hips, and the bladder.
Top
How should I prepare
for the procedure?
Because the strong magnetic field used for MRI will pull
on any ferromagnetic metal object implanted in the body,
MRI staff will ask whether you have a prosthetic hip,
heart pacemaker (or artificial heart valve), implanted
port, infusion catheter (brand names Port-o-cath, Infusaport,
Lifeport), intrauterine device (IUD), or any metal plates,
pins, screws, or surgical staples in your body. In most
cases, surgical staples, plates, pins and screws pose
no risk during MRI if they have been in place for more
than four to six weeks. Tattoos and permanent eyeliner
may also create a problem. You will be asked if you have
ever had a bullet or shrapnel in your body, or ever worked
with metal. If there is any question of metal fragments,
you may be asked to have an x-ray that will detect any
such metal objects. Tooth fillings usually are not affected
by the magnetic field, but they may distort images of
the facial area or brain, so the radiologist should be
aware of them. The same is true of braces, which may make
it hard to "tune" the MRI unit to your body.
You will be asked to remove anything that might degrade
MRI images of the head, including hairpins, jewelry, eyeglasses,
hearing aids, and any removable dental work.
The radiologist or technologist may ask
about drug allergies and whether head surgery has been
done in the past. If you might be pregnant, this should
be mentioned. Some patients who undergo MRI in an enclosed
unit may feel confined or claustrophobic. If you are not
easily reassured, a sedative may be administered. Roughly
one in 20 patients will require medication to reduce the
anxiety associated with claustrophobia.
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What does the MRI
equipment look like?
The conventional MRI unit is a closed cylindrical magnet
in which the patient must lie totally still for several
seconds at a time, and consequently may feel "closed-in"
or truly claustrophobic. However, new "patient-friendly"
designs are rapidly coming into routine use.
The "short-bore" systems are
wider and shorter and do not fully enclose the patient.
Some newer units are open on all sides, however the image
quality may vary.
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How
does the procedure work?
MRI is a unique imaging method because, unlike the usual
radiographs (x-rays), radioisotope studies, or even Computed
Tomography (CT) scanning, it does not rely on ionizing
radiation. Instead, radiofrequency waves are directed
at protons, the nuclei of hydrogen atoms, in a strong
magnetic field. The protons are first "excited"
and then "relaxed," emitting radio signals that
can be computer-processed to form an image. In the body,
protons are most abundant in the hydrogen atoms of water
— the "H" of H2O — so that an MRI
image shows differences in the water content and distribution
in various body tissues. Even different types of tissue
within the same organ, such as the gray and white matter
of the brain, can easily be distinguished. Typically an
MRI examination consists of two to six imaging sequences,
each lasting two to 15 minutes. Each sequence has its
own degree of contrast and shows a cross-section of the
body in one of several planes (right to left, front to
back, upper to lower).
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How
is the procedure performed?
The patient is placed on a sliding table and positioned
comfortably for the MRI examination. Then the radiologist
and technologist leave the room and the individual MRI
sequences are performed. The patient is able to communicate
with the radiologist or technologist at any time using
an intercom. Also, many MRI centers allow a friend or,
if a child is being examined, a parent to stay in the
room. Depending on how many images are needed, the exam
will generally take 15 to 45 minutes, although a very
detailed study may take longer. You will be asked not
to move during the actual imaging process, but between
sequences some movement is allowed. Patients are generally
required to remain still for only a few seconds to a few
minutes at a time.
Depending on the part of the body being
examined, a contrast material may be used to enhance the
visibility of certain tissues or blood vessels. A small
needle connected to an intravenous line is placed in an
arm or hand vein. A saline solution will drip through
the intravenous line to prevent clotting until the contrast
material is injected, about two-thirds of the way through
the exam.
When the exam is over the patient is asked
to wait until the images are examined to determine if
more images are needed. A radiologist experienced in MRI
will analyze the images and send a report with his or
her interpretation to the patient's personal physician.
This should take only a few days or less.
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What
will I experience during the MRI procedure?
MRI causes no pain, but some patients can find it uncomfortable
to remain still during the examination. Others experience
a sense of being "closed in," though the more
open construction of newer MRI systems has done much to
reduce that reaction. You may notice a warm feeling in
the area under examination; this is normal, but if it
bothers you the radiologist or technologist should be
notified.
If a contrast injection is needed, there
may be discomfort at the injection site, and you may have
a cool sensation at the site during the injection. Most
bothersome to many patients are the loud tapping or knocking
noises heard at certain phases of imaging. Ear plugs may
help.
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Who interprets the results and how do
I get them?
A radiologist, who is a physician experienced in MRI and
other radiology examinations, will analyze the images
and send a signed report with his or her interpretation
to the patient's personal physician. The patient receives
MRI results from the referring physician who ordered the
test. New technology also allows for distribution of diagnostic
reports and referral images over the Internet at many
facilities.
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What
are the benefits vs. risks?
Benefits
Images of the soft-tissue structures of the body—such
as the heart, lungs, liver, and other organs—are
clearer and more detailed than with other imaging methods.
MRI can help physicians evaluate the function as well
as the structure of many organs.
The detail makes MRI an invaluable tool in early diagnosis
and evaluation of tumors.
MRI contrast material is less likely to produce an allergic
reaction than the iodine-based materials used for conventional
x-rays and CT scanning.
MRI enables the detection of abnormalities that might
be obscured by bone with other imaging methods.
MRI provides a fast, noninvasive alternative to x-ray
angiography for diagnosing problems of the heart and cardiovascular
system.
Exposure to radiation is avoided.
Risks
An undetected metal implant may be affected by the strong
magnetic field.
MRI is generally avoided in the first 12 weeks of pregnancy.
Doctors usually use other methods of imaging—such
as ultrasound—on pregnant women, unless there is
a strong medical reason to use MRI.
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What
are the limitations of MRI of the Body?
Bone is better imaged by conventional x-rays in some cases,
and CT is preferred for patients with severe bleeding.
MRI may not always distinguish between tumor tissue and
edema fluid, and does not detect calcium when this is
present within a tumor. In most cases the examination
is safe for patients with metal implants, with the exception
of a few types of implants, so patients should inform
the technician of an implant prior to the test. The examination
must be used cautiously in early pregnancy. MRI typically
costs more than CT scanning.
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Copyright © 2004 Radiological Society
of North America, Inc. (RSNA)
--------------------------------------------------------------------------------
What is CT Scanning
of the Body?
CT (computed tomography), sometimes called CAT scan, uses
special x-ray equipment to obtain image data from different
angles around the body, and then uses computer processing
of the information to show a cross-section of body tissues
and organs.
CT imaging is particularly useful because
it can show several types of tissue—lung, bone,
soft tissue and blood vessels—with great clarity.
Using specialized equipment and expertise to create and
interpret CT scans of the body, radiologists can more
easily diagnose problems such as cancers, cardiovascular
disease, infectious disease, trauma and musculoskeletal
disorders.
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What
are some common uses of the procedure?
Because it provides detailed, cross-sectional views of
all types of tissue, CT is one of the best tools for studying
the chest and abdomen. It is often the preferred method
for diagnosing many different cancers, including lung,
liver and pancreatic cancer, since the image allows a
physician to confirm the presence of a tumor and measure
its size, precise location, and the extent of the tumor's
involvement with other nearby tissue. CT examinations
are often used to plan and properly administer radiation
treatments for tumors, to guide biopsies and other minimally
invasive procedures, and to plan surgery and determine
surgical resectability. CT can clearly show even very
small bones, as well as surrounding tissues such as muscle
and blood vessels. This makes it invaluable in diagnosing
and treating spinal problems and injuries to the hands,
feet and other skeletal structures. CT images can also
be used to measure bone mineral density for the detection
of osteoporosis. In cases of trauma, CT can quickly identify
injuries to the liver, spleen, kidneys, or other internal
organs. Many dedicated shock-trauma centers have a CT
scanner in the emergency room. CT can also play a significant
role in the detection, diagnosis and treatment of vascular
diseases that can lead to stroke, kidney failure, or even
death.
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How
should I prepare for the CAT scan?
You should wear comfortable, loose-fitting clothing for
your CT exam. Metal objects can affect the image, so avoid
clothing with zippers and snaps. You may also be asked
to remove hairpins, jewelry, eyeglasses, hearing aids
and any removable dental work, depending on the part of
the body that is being scanned. You may be asked not to
eat or drink anything for one or more hours before the
exam. Women should always inform their doctor or x-ray
technologist if there is any possibility that they are
pregnant.
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What
does the equipment look like?
The CT scanner is a large, square machine with a hole
in the center, something like a doughnut. The patient
lies still on a table that can move up or down, and slide
into and out from the center of the hole. Within the machine,
an x-ray tube on a rotating gantry moves around the patient's
body to produce the images, making clicking and whirring
noises as the table moves. Though the technologist will
be able to see and speak to you, you will be alone in
the room during the exam.
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How
does the procedure work?
In many ways, CT scanning works very much like other x-ray
examinations. Very small, controlled amounts of x-ray
radiation are passed through the body, and different tissues
absorb radiation at different rates. With plain radiology,
when special film is exposed to the absorbed x-rays, an
image of the inside of the body is captured. With CT,
the film is replaced by an array of detectors, which measure
the x-ray profile.
Inside the CT scanner is a rotating gantry
that has an x-ray tube mounted on one side and an arc-shaped
detector mounted on the opposite side. An x-ray beam is
emitted in a fan shape as the rotating frame spins the
x-ray tube and detector around the patient. Each time
the x-ray tube and detector make a 360 degree rotation
and the x-ray passes through the patient's body, the image
of a thin section is acquired. During each rotation, the
detector records about 1,000 images (profiles) of the
expanded x-ray beam. Each profile is then reconstructed
by a dedicated computer into a two-dimensional image of
the section that was scanned. Multiple computers are typically
used to control the entire CT system.
You might think of it as looking into
a loaf of bread by cutting the bread into thin slices.
When the image slices are reassembled by computer, the
result is a very detailed, multidimensional view of the
body's interior.
A relatively new technique, spiral (helical)
CT has improved the accuracy of CT for many diseases.
A new vascular imaging technique—spiral CT angiography—is
noninvasive and less expensive than conventional angiography,
and allows doctors to see blood vessels without the need
for more invasive procedures.
The term "spiral CT" comes from
the shape of the path taken by the x-ray beam during scanning.
The examination table advances at a constant rate through
the scanner gantry while the x-ray tube rotates continuously
around the patient, tracing a spiral path through the
patient. This spiral path gathers continuous data with
no gaps between images.
With spiral CT, refinements in detector
technology support faster, higher-quality image acquisition
with less radiation exposure. The current spiral CT scans
are called multidetector CT and are most commonly four-
or 16-slice systems. CT scanners with 32, 40 and 64 detectors
are currently under development and are becoming available.
These instruments should provide either faster scanning
or higher resolution images. Using 16-slice scanner systems
the radiologist can acquire 32 image slices per second.
A spiral scan can usually be obtained during a single
breath hold. This allows allows scanning of the chest
or abdomen in 10 seconds or less. Such speed is beneficial
in all patients but especially in elderly, pediatric or
critically ill patients, populations in whom the length
of scanning was often problematic. The multidetector CT
also allows applications like CT angiography to be more
successful.
With conventional CT, small lesions may
go undetected when a patient breathes differently on consecutive
scans, as a lesion may be missed by unequal spacing between
scans. The speed of spiral scanning and a single breath
hold increase the rate of lesion detection.
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How is
the CAT scan performed?
The technologist begins by positioning the patient on
the CT table. The patient's body may be supported by pillows
to help hold it still and in the proper position during
the scan. As the study proceeds, the table will move slowly
into the CT scanner "doughnut." Depending on
the area of the body being examined, the increments of
movement may be so small that they are almost undetectable,
or large enough that the patient feels the sensation of
motion.
A CT examination often requires the use
of different contrast materials to enhance the visibility
of certain tissues or blood vessels. The contrast material
may be injected through an IV directly into the blood
stream, swallowed or administered by enema, depending
on the type of examination. Before administering the contrast
material, the radiologist or technologist will ask whether
the patient has any allergies, especially to medications
or iodine, and whether the patient has a history of diabetes,
asthma, a heart condition, kidney problems, or thyroid
conditions. These conditions may indicate a higher risk
of reaction to the contrast material or potential problems
eliminating the material from the patient's system after
the exam.
A CT examination usually takes five minutes
to half an hour. When the exam is over, the patient may
be asked to wait until the images are examined to determine
if more images are needed.
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What
will I experience during the procedure?
CT scanning causes no pain, and with spiral CT, the need
to lie still for any length of time is reduced. For different
parts of the body, the patient preparation will be different.
You may be asked to swallow either water or a positive
contrast material, a liquid that allows the radiologist
to better see the stomach, small bowel and colon. Some
patients find the taste of the contrast material mildly
unpleasant, but most can easily tolerate it. Your exam
may require the administration of the material by enema
if the colon is the focus of the study. You will experience
a sense of abdominal fullness and may feel an increasing
need to expel the liquid. Be patient; the mild discomfort
will not last long.
Commonly, a contrast material is injected
into a vein to better define the blood vessels and kidneys,
and to accentuate the appearance between normal and abnormal
tissue in organs like the liver and spleen. Some people
report feeling a flush of heat and sometimes a metallic
taste in the back of the mouth. These sensations usually
disappear within a minute or two. Some people experience
a mild itching sensation. If it persists or is accompanied
by hives (small bumps on the skin), the itch can be treated
easily with medication. In very rare cases, a patient
may become short of breath or experience swelling in the
throat or other parts of the body. These can be indications
of a more serious reaction to the contrast material that
should be treated promptly, so tell the technologist immediately
if you experience these symptoms. Fortunately, with the
safety of the newest contrast materials, these adverse
effects are very rare.
You will be alone in the room during the
scan; however, the technologist can see, hear and speak
with you at all times. In pediatric patients, a parent
may be allowed in the room with the patient to alleviate
fear, but will be required to wear a lead apron to prevent
radiation exposure.
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Who
interprets the results and how do I get them?
A radiologist, who is a physician experienced in CT and
other radiology examinations, will analyze the images
and send a signed report with his or her interpretation
to the patient's personal physician. The personal physician's
office will inform the patient on how to obtain their
results. New technology also allows for distribution of
diagnostic reports and referral images over the Internet
at some facilities.
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What
are the benefits vs. risks?
Benefits
Unlike other imaging methods, CT scanning offers detailed
views of many types of tissue, including the lungs, bones,
soft tissues and blood vessels.
CT scanning is painless, noninvasive and accurate.
CT examinations are fast and simple. For example, in trauma
cases, they can reveal internal injuries and bleeding
quickly enough to help save lives.
Diagnosis made with the assistance of CT can eliminate
the need for invasive exploratory surgery and surgical
biopsy.
CT scanning can identify both normal and abnormal structures,
making it a useful tool to guide radiotherapy, needle
biopsies and other minimally invasive procedures.
CT has been shown to be a cost-effective imaging tool
for a wide range of clinical problems.
Risks
CT does involve exposure to radiation in the form of x-rays,
but the benefit of an accurate diagnosis far outweighs
the risk. The effective radiation dose from this procedure
is about 10 mSv, which is about the same as the average
person receives from background radiation in three years.
See the Safety page for more information about radiation
dose.
Special care is taken during x-ray examinations to ensure
maximum safety for the patient by shielding the abdomen
and pelvis with a lead apron, with the exception of those
examinations in which the abdomen and pelvis are being
imaged. Women should always inform their doctor or x-ray
technologist if there is any possibility that they are
pregnant.
Nursing mothers should wait for 24 hours after contrast
injection before resuming breast feeding.
The risk of serious allergic reaction to iodine-containing
contrast material is rare, and radiology departments are
well equipped to deal with them.
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What
are the limitations of CT Scanning of the Body?
Very fine soft-tissue details in areas such as the knee
or shoulder can be more readily and clearly seen with
magnetic resonance imaging (MRI). The exam is not generally
indicated for pregnant women.
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Copyright © 2004 Radiological Society of North
America, Inc. (RSNA)
--------------------------------------------------------------------------------
What
is Positron Emission Tomography?
Positron emission tomography, also called PET imaging
or a PET scan, is a diagnostic examination that involves
the acquisition of physiologic images based on the detection
of positrons. Positrons are tiny particles emitted from
a radioactive substance administered to the patient.
The subsequent views of the human body developed by
this technique are used to evaluate a variety of diseases.
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What are some
common uses of the procedure?
PET scans are used most often to detect cancer and to
examine the effects of cancer therapy by characterizing
biochemical changes in the cancer. These scans are performed
on the whole body. PET scans of the heart can be used
to determine blood flow to the heart muscle and help
evaluate signs of coronary artery disease. PET scans
of the heart can also be used to determine if areas
of the heart that show decreased function are alive
rather than scarred due to a prior heart attack, called
a myocardial infarction. Combined with a myocardial
perfusion study, PET scans differentiate nonfunctioning
heart muscle from heart muscle that would benefit from
a procedure, such as angioplasty or coronary artery
bypass surgery, which would reestablish adequate blood
flow and improve heart function. PET scans of the brain
are used to evaluate patients who have memory disorders
of an undetermined cause; who have suspected or proven
brain tumors; or who have seizure disorders that are
not responsive to medical therapy and, therefore, are
candidates for surgery.
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How should I
prepare for the procedure?
PET is usually done on an outpatient basis. Your doctor
will give you detailed instructions on how to prepare
for your examination. You should wear comfortable, loose-fitting
clothes. You should not eat for four hours before the
scan. You will be encouraged to drink water. Your doctor
will instruct you regarding the use of medications before
the test.
Note: Diabetic patients should ask for any specific
diet guidelines to control glucose levels during the
day of the test.
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What does the
equipment look like?
You will be taken to an examination room that houses
the PET scanner, which has a hole in the middle and
looks like a large doughnut. Within this machine are
multiple rings of detectors that record the emission
of energy from the radioactive substance in your body
and permit an image of your body to be obtained. While
lying on a cushioned examination table, you will be
moved into the hole of the machine. The images are displayed
on the monitor of a nearby computer, which is similar
in appearance to the personal computer you may have
in your home.
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How does the
procedure work?
Before the examination begins, a radioactive substance
is produced in a machine called a cyclotron and attached,
or tagged, to a natural body compound, most commonly
glucose, but sometimes water or ammonia. Once this substance
is administered to the patient, the radioactivity localizes
in the appropriate areas of the body and is detected
by the PET scanner.
Different colors or degrees of brightness on a PET
image represent different levels of tissue or organ
function. For example, because healthy tissue uses glucose
for energy, it accumulates some of the tagged glucose,
which will show up on the PET images. However, cancerous
tissue, which uses more glucose than normal tissue,
will absorb more of the substance and appear brighter
than normal tissue on the PET images.
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How is the procedure
performed?
A nurse or technologist will take you into a special
PET examination room. You will lie down on an examination
table and be given the radioactive substance as an intravenous
injection (although, in some cases, it will be given
through an existing intravenous line or inhaled as a
gas). It will then take approximately 30 to 60 minutes
for the substance to travel through your body and be
absorbed by the tissue under study. During this time,
you will be asked to rest quietly in a partially darkened
room and to avoid significant movement or talking, which
may alter the localization of the administered substance.
After that time, scanning begins. This takes an additional
30 to 45 minutes.
Some patients, specifically those with heart disease,
may undergo a stress test in which PET scans are obtained
while they are at rest, and again after undergoing the
administration of a pharmaceutical to alter the blood
flow to the heart.
Usually, there are no restrictions on daily routine
after the test, although you should drink plenty of
fluids to flush the radioactive substance from your
body.
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What will I
experience during the procedure?
The administration of the radioactive substance will
feel like a slight pinprick if given by intravenous
injection. You will then be made as comfortable as possible
on the examination table before you are positioned in
the PET scanner for the test. You will be asked to remain
still for the duration of the examination. Patients
who are claustrophobic may feel some anxiety while positioned
in the scanner. Also, some patients find it uncomfortable
to hold one position for more than a few minutes. You
will not feel anything related to the radioactivity
of the substance in your body.
Top
Who interprets
the results and how do I get them?
Patients undergo PET because their referring physician
has recommended it. A radiologist who has specialized
training in PET will interpret the images and forward
a report to your referring physician. It usually takes
one to three days to interpret, report, and deliver
the results. In order to facilitate interpretation,
you may be asked to bring any outside examinations with
you, such as recent CT (CAT) scans or MRI scans.
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What are the
benefits vs. risks?
Because PET allows study of body function, it can help
physicians detect alterations in biochemical processes
that suggest disease before changes in anatomy are apparent
on other imaging tests such as CT or MRI scans.
Because the radioactivity is very short-lived, your
radiation exposure is extremely low. The substance amount
is so small that it does not affect the normal processes
of the body.
The radioactive substance may expose radiation to the
fetus of patients who are pregnant or the infants of
women who are breast-feeding. The risk to the fetus
or infant should be considered related to the potential
information gain from the result of the PET examination.
If you are pregnant you should inform the PET imaging
staff before the examination is performed.
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What are the
limitations of Positron Emission Tomography?
PET can give false results if a patient's chemical balances
are not normal. Specifically, test results of diabetic
patients or patients who have eaten within several hours
prior to the examination can be adversely affected because
of blood sugar or blood insulin levels.
Also, because the radioactive substance decays quickly
and is effective for a short period of time, it must
be produced in a laboratory near the PET scanner. It
is important to be on time for the appointment and to
receive the radioactive substance at the scheduled time.
PET must be done by a radiologist who has specialized
in nuclear medicine and has substantial experience with
PET. Most large medical centers now have PET services
available to their patients. Medicare and insurance
companies cover many of the applications of PET, and
coverage continues to increase.
Finally, the value of a PET scan is enhanced when it
is part of a larger diagnostic work-up. This often entails
comparison of the PET scan with other imaging studies
such as CT or MRI.
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Copyright © 2004 Radiological Society of North
America, Inc. (RSNA)
--------------------------------------------------------------------------------
What is Radiography-based
(X-ray) Bone Densitometry?
Every day, physicians use radiography, or x-rays, to
view and evaluate bone fractures and other injuries
of the musculoskeletal system. However, a plain x-ray
test is not the best way to assess bone density. To
detect osteoporosis accurately, doctors use an enhanced
form of x-ray technology called dual-energy x-ray absorptiometry
(DXA or DEXA). DEXA bone densitometry is today's established
standard for measuring bone mineral density (BMD). DEXA
is a quick, painless procedure for measuring bone loss.
Measurement of the lower spine and hips are most often
done. More portable devices that measure the wrist,
fingers or heel are sometimes used for screening, including
some that use ultrasound waves rather than x-rays.
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What are some
common uses of the procedure?
DEXA bone densitometry is used most often to diagnose
osteoporosis, a condition that often affects women after
menopause, but may also be found in men. Osteoporosis
involves a gradual loss of calcium, causing the bones
to become thinner, more fragile, and more likely to
break. The DEXA test can also assess your risk for developing
fractures. If your bone density is found to be low,
you and your physician can work together on a treatment
plan to help prevent fractures before they occur. DEXA
is also effective in tracking the effects of treatment
for osteoporosis or for other conditions that cause
bone loss. Bone density testing is strongly recommended
if you:
are a post-menopausal woman and not taking estrogen.
have a personal or maternal history of hip fracture
or smoking.
are a post-menopausal woman who is tall (over 5 feet
7 inches) or thin (less than 125 pounds).
are a man with clinical conditions associated with bone
loss.
use medications that are known to cause bone loss, including
corticosteroids such as Prednisone, various anti-seizure
medications such as Dilantin and certain barbiturates,
or high-dose thyroid replacement drugs.
have type 1 (formerly called juvenile or insulin-dependent)
diabetes, liver disease, kidney disease, or a family
history of osteoporosis.
have high bone turnover, which shows up in the form
of excessive collagen in urine samples.
have a thyroid condition, such as hyperthyroidism.
have experienced a fracture after only mild trauma.
have had x-ray evidence of vertebral fracture or other
signs of osteoporosis.
Top
How should I
prepare for the procedure?
On the day of the exam, eat normally, but don't take
calcium supplements for at least 24 hours beforehand.
Wear loose, comfortable clothing, avoiding garments
that have zippers, belts, or buttons made of metal.
Inform your physician if you recently had a barium examination
or have been injected with a contrast material for a
computed tomography (CT) scan or radioisotope scan;
you may have to wait 10-14 days before undergoing a
DEXA test. Women should always inform their physician
or x-ray technologist if there is a possibility they
are pregnant.
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What does the
DEXA equipment look like?
There are two types of DEXA equipment: the central device
and the peripheral device. Central DEXA devices measure
bone density in the hip and spine, while peripheral
devices measure it in the wrist, heel, or finger. The
central DEXA device is used in hospitals and medical
offices, while the smaller peripheral device is available
in drugstores and on mobile health vans in the community.
CT scanners also can be used effectively to evaluate
the spine and hip for osteoporosis.
Central devices have a large, flat table and an "arm"
suspended overhead. The arm swings away so that the
table can be used as a treatment table or exam chair
for routine patient examinations. The peripheral DEXA
(pDEXA) device weighs only about 60 pounds. It is a
portable box-like structure that includes a space to
insert your foot or forearm for imaging.
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How does
the procedure work?
The DEXA machine sends a thin, invisible beam of low-dose
x-rays through your bones via two energy streams. It
relies on two distinct energy peaks: one peak is absorbed
mainly by soft tissue and the other by bone. The soft
tissue amount can be subtracted from the total, and
what remains is a patient's bone mineral density.
All devices feature special software to compute the
data and display them on a computer monitor, allowing
your doctor to make an accurate diagnosis. The amount
of radiation used is extremely small—less than
one tenth the dose of a standard chest x-ray.
Top
How is the procedure
performed?
The DEXA bone density test takes between 10 and 30 minutes,
depending on the equipment used and the parts of the
body being examined. You may be asked to undress and
put on a hospital gown. Then, you'll lie on a padded
table with an x-ray generator below and a detector (an
imaging device) above.
Most often, doctors focus on bone loss in the spine
and hip where most osteoporosis-related fractures happen.
During an examination of the spine, your legs will be
supported on a padded box to flatten your pelvis and
lower (lumbar) spine. To assess your hip, the technologist
will place your foot in a brace that rotates the hip
inward. In both cases, the detector is slowly passed
over the area, generating images on a computer monitor.
The peripheral DEXA (pDEXA) test is even simpler. You
place your finger, hand, forearm or foot in a small
device, and a bone density reading is obtained within
a few minutes. These tests may not be as sensitive—especially
in younger people—and cannot be used to monitor
response to treatment.
Top
What will I
experience during the x-ray procedure?
DEXA bone densitometry is a simple, non-invasive procedure.
Once on the table, you may be asked to hold an awkward
position for a short time while the arm of the machine
passes over your body taking measurements. It is important
that you stay as still as possible during the procedure
to ensure a clear, useful image. No anesthesia is required.
The procedure is painless, and radiation exposure is
minimal.
Top
Who interprets
the results and how do I get them?
The results of a DEXA bone density exam are interpreted
by a radiologist, who is a physician specially trained
to diagnose conditions and diseases by obtaining and
interpreting medical images. The radiologist will send
an interpretation of your results and a signed report
to your primary care physician, who will work with you
to develop a treatment plan. Usually available within
a few days, your test results will be in the form of
two scores:
T score — This number shows the amount of bone
you have compared to a young adult of the same gender
with peak bone mass. A score above -1 is considered
normal. A score between -1 and -2.5 is classified as
osteopenia, the first stage of bone loss. A score below
-2.5 is defined as osteoporosis. It is used to estimate
your risk of developing a fracture.
Z score — This number reflects the amount of
bone you have compared to other people in your age group
and of the same size and gender. If it is unusually
high or low, it may indicate a need for further medical
tests.
Top
What are the
benefits vs. risks?
Benefits
DEXA bone density testing is the most accurate method
available for the diagnosis of osteoporosis. It is also
considered an accurate estimator of fracture risk. It
will not tell whether you will or will not have a fracture,
but gives relative risk of suffering a fracture, just
as cholesterol and blood pressure help determine risk
for heart disease. A low reading should not cause you
to be anxious, but may help you set healthy goals. As
with other diseases and conditions, early detection
is the key to prevention of further bone loss and eventual
fractures. DEXA equipment is widely available, making
DEXA bone densitometry testing convenient for patients
and doctors alike.
Risks
No complications are expected with the DEXA procedure.
Top
What are the
limitations of DEXA Bone Densitometry?
Despite its effectiveness as a method of measuring bone
density, DEXA is of limited use in people with a spinal
deformity or those who have had previous spinal surgery.
The presence of vertebral compression fractures or osteoarthritis
may interfere with the accuracy of the test. CT scans
may be more useful in such instances. DEXA cannot predict
who will experience a fracture, but can provide indications
of relative risk.
Central DEXA devices are more sensitive than pDEXA devices,
but they are also somewhat more expensive. The peripheral
devices don't accurately follow changes in your bones
during therapy. A test done on a peripheral location,
such as your heel or wrist, may help predict the risk
of fracture in your spine or hip. But because bone mass
tends to vary from one location to the other, measuring
the heel is not as accurate as measuring the spine or
hip.
Top
Copyright © 2004 Radiological Society of North
America, Inc. (RSNA)
--------------------------------------------------------------------------------
What is General
Ultrasound Imaging?
Ultrasound (US) imaging, also called ultrasound scanning
or sonography, is a method of obtaining images from
inside the human body through the use of high frequency
sound waves. The reflected sound wave echoes are recorded
and displayed as a real-time visual image. No ionizing
radiation (x-ray) is involved in ultrasound imaging.
Obstetric ultrasound refers to the specialized use of
sound waves to visualize and thus determine the condition
of a pregnant woman and her embryo or fetus.
Ultrasound is a useful way of examining many of the
body's internal organs, including the heart, liver,
gallbladder, spleen, pancreas, kidneys, and bladder.
Because ultrasound images are captured in real-time,
they can show movement of internal tissues and organs,
and enable physicians to see blood flow and heart valve
functions. This can help to diagnose a variety of heart
conditions and to assess damage after a heart attack
or other illness.
Top
What are some
common uses of the procedure?
Millions of expectant parents have seen the first "picture"
of their unborn child with pelvic ultrasound examinations
of the uterus and fetus. Ultrasound imaging is used
extensively for evaluating the eyes, pelvic and abdominal
organs, heart, and blood vessels, and can help a physician
determine the source of pain, swelling, or infection
in many parts of the body. Because ultrasound provides
real-time images, it can also be used to guide procedures
such as needle biopsies, in which needles are used to
sample cells from organs for laboratory testing. Ultrasound
is now being used to image the breasts and to guide
biopsy of breast cancer (see the Ultrasound-Guided Breast
Biopsy page). Ultrasound is also used to evaluate superficial
structures, such as the thyroid gland and scrotum (testicles).
Doppler ultrasound is a special technique used to examine
blood flow. Doppler images can help the physician to
see and evaluate:
Blockages to blood flow (such as clots).
Build-up of plaque inside the vessel.
Congenital malformation.
Top
How should
I prepare for the procedure?
You should wear comfortable, loose-fitting clothing
for your ultrasound exam. Other preparation depends
on the type of examination you will have. For some scans,
your doctor may instruct you not to eat or drink for
as many as 12 hours before your appointment. For others,
you may be asked to drink up to six glasses of water
two hours prior to your exam and avoid urinating, so
that your bladder is full when the scan begins.
Top
What does the
equipment look like?
Ultrasound scanners consist of a console containing
a computer and electronics, a video display screen and
a transducer that is used to scan the body. The transducer
is a small, hand-held device about the size of a bar
of soap, attached to the scanner by a cord. The physician
or technologist spreads a lubricating gel on the patient's
abdomen in the area being examined, and then presses
the transducer firmly against the skin to obtain images.
The ultrasound image is immediately visible on a nearby
screen that looks much like a computer or television
monitor. The physician or technologist watches this
screen during an examination and captures representative
images for storage. Often, the patient is able to see
it as well.
Top
How does
the procedure work?
Ultrasound imaging is based on the same principles involved
in the sonar used by bats, ships at sea, and anglers
with fish detectors. As the sound passes through the
body, echoes are produced that can be used to identify
how far away an object is, how large it is, its shape,
and its consistency (fluid, solid or mixed).
The ultrasound transducer functions as both a generator
of sound (like a speaker) and a detector (like a microphone).
When the transducer is pressed against the skin, it
directs inaudible, high-frequency sound waves into the
body. As the sound echoes from the body’s fluids
and tissues, the transducer records the strength and
character of the reflected waves. With Doppler ultrasound,
the microphone captures and records tiny changes in
the sound wave's pitch and direction of the sound. These
echoes are instantly measured and displayed by a computer,
which in turn creates a real-time picture on the monitor.
The live images of the examination are usually recorded
on videotape, but one or more frames of the moving picture
may be "frozen" to capture a still image.
Top
How is the procedure
performed?
The patient is usually positioned on an examination
table. A clear gel is applied to the patient's body
in the area to be examined, to help the transducer make
secure contact with the skin. The sound waves produced
by the transducer cannot penetrate air, so the gel helps
eliminate air pockets between the transducer and the
skin. The technologist or radiologist presses the transducer
firmly against the skin and sweeps it back and forth
to image the area of interest.
When the examination is complete, the patient may be
asked to dress and wait while the ultrasound images
are reviewed, either on film or on a TV monitor. Often,
though, the technologist or radiologist is able to review
the ultrasound images in real time as they are acquired,
and the patient can be released immediately.
Top
What will I
experience during the procedure?
Most ultrasound examinations are painless, fast, and
easy. You will lie on your back on an examining table.
The technologist or doctor will spread some warm gel
on your skin and then press the transducer firmly against
your body, moving it until the desired images are captured.
There may be varying degrees of discomfort from pressure
as the technologist guides the transducer over your
abdomen, especially if you are required to have a full
bladder. The examination usually takes less than 30
minutes.
Top
Who interprets
the results and how do I get them?
A radiologist, or other physicians experienced in ultrasound
and other radiology examinations, will analyze the images
and send a signed report with his or her interpretation
to the patient’s personal physician. The patient
receives ultrasound results from the referring physician
who ordered the test results. In some cases the radiologist
may discuss preliminary results with you at the conclusion
of your examination. New technology also allows for
distribution of diagnostic reports and referral images
over the Internet at many facilities.
Top
What are
the benefits vs. risks?
Benefits
Ultrasound scanning is noninvasive (no needles or injections,
in most cases) and is usually painless.
Ultrasound is widely available and easy to use.
Ultrasound uses no ionizing radiation, and is the preferred
image modality for diagnosis and monitoring of pregnant
women and their unborn infants.
Ultrasound provides real-time imaging, making it a good
tool for guiding minimally invasive procedures such
as needle biopsies.
Ultrasound images can visualize structure, movement
and live function in the body's organs and blood vessels.
Risks
For standard diagnostic ultrasound there are no known
harmful effects on humans.
Top
What are the
limitations of General Ultrasound Imaging?
Ultrasound has difficulty penetrating bone and therefore
can only see the outer surface of bony structures and
not what lies within. For visualization of bone, other
imaging modalities, such as magnetic resonance imaging
(MRI), may be selected.
Ultrasound waves do not pass through air; therefore
an evaluation of the stomach, small intestine and large
intestine may be limited. Intestinal gas may also prevent
visualization of deeper structures such as the pancreas
and aorta. Patients suffering from obesity are more
difficult to image—this is because tissue attenuates
(weakens) the sound waves as they pass deeper into the
body.
Top
Copyright © 2004 Radiological Society of North
America, Inc. (RSNA)
--------------------------------------------------------------------------------
What is Mammography?
Mammography is a specific type of imaging that uses
a low-dose x-ray system for examination of the breasts.
The images of the breasts can be viewed on film at a
view box or as soft copy on a digital mammography work
station. Most medical experts agree that successful
treatment of breast cancer often is linked to early
diagnosis. Mammography plays a central part in early
detection of breast cancers because it can show changes
in the breast up to two years before a patient or physician
can feel them. Current guidelines from the U.S. Department
of Health and Human Services (HHS), the American Cancer
Society (ACS), the American Medical Association (AMA)
and the American College of Radiology (ACR) recommend
screening mammography every year for women, beginning
at age 40.
The National Cancer Institute (NCI) adds that women
who have had breast cancer and those who are at increased
risk due to a genetic history of breast cancer should
seek expert medical advice about whether they should
begin screening before age 40 and about the frequency
of screening.
Top
What are some
common uses of the procedure?
Mammography is used to aid in the diagnosis of breast
diseases in women. Screening mammography can assist
your physician in the detection of disease even if you
have no complaints or symptoms.
Initial mammographic images themselves are not always
enough to determine the existence of a benign or malignant
disease with certainty. If a finding or spot seems suspicious,
your radiologist may recommend further diagnostic studies.
Diagnostic mammography is used to evaluate a patient
with abnormal clinical findings, such as a breast lump
or lumps, that have been found by the woman or her doctor.
Diagnostic mammography may also be done after an abnormal
screening mammography in order to determine the cause
of the area of concern on the screening exam.
Top
How should I prepare
for a mammogram?
Before scheduling a mammogram, the ACS and other specialty
organizations recommend that you discuss any new findings
or problems in your breasts with your doctor. In addition,
inform your doctor of any prior surgeries, hormone use,
and family or personal history of breast cancer.
Do not schedule your mammogram for the week before
your period if your breasts are usually tender during
this time. The best time is one week following your
period. Always inform your doctor or x-ray technologist
if there is any possibility that you are pregnant.
The ACS also recommends you:
Do not wear deodorant, talcum powder, or lotion under
your arms or on your breasts on the day of the exam.
These can appear on the x-ray film as calcium spots.
Describe any breast symptoms or problems to the technologist
performing the exam.
If possible, obtain prior mammograms and make them available
to the radiologist at the time of the current exam.
Ask when your results will be available; do not assume
the results are normal if you do not hear from your
doctor or the mammography facility.
In addition, before the examination, you will be asked
to remove all jewelry and clothing above the waist and
you will be given a gown or loose-fitting material that
opens in the front.
Top
What does the
Mammography equipment look like?
A mammography unit is a rectangular box that houses
the tube in which x-rays are produced. The unit is dedicated
equipment because it is used exclusively for x-ray exam
of the breast, with special accessories that allow only
the breast to be exposed to the x-rays. Attached to
the unit is a device that holds and compresses the breast
and positions it so images can be obtained at different
angles.
Top
How does the
procedure work?
The breast is exposed to a small dose of radiation to
produce an image of internal breast tissue. The image
of the breast is produced as a result of some of the
x-rays being absorbed (attenuation) while others pass
through the breast to expose either a film (conventional
mammography) or digital image receptor (digital mammography).
The exposed film is either placed in a developing machine—producing
images much like the negatives from a 35mm camera—or
images are digitally stored on computer.
Top
How is the procedure
performed?
During mammography, a specially qualified radiologic
technologist will position you to image your breast.
The breast is first placed on a special platform and
compressed with a paddle (often made of clear Plexiglas
or other plastic).
Breast compression is necessary in order to:
Even out the breast thickness so that all of the tissue
can be visualized;
Spread out the tissue so that small abnormalities won't
be obscured by overlying breast tissue;
Allow the use of a lower x-ray dose since a thinner
amount of breast tissue is being imaged;
Hold the breast still in order to eliminate blurring
of the image caused by motion;
Reduce x-ray scatter to increase sharpness of picture.
The technologist will go behind a glass shield while
making the x-ray exposure, which will send a beam of
x-rays through the breast to the film behind the plate,
thus exposing the film.
You will be asked to change positions slightly between
images. The routine views are a top-to-bottom view and
a side view. The process is repeated for the other breast.
The examination process should take about half an hour.
When the mammography is completed you will be asked
to wait until the technologist examines the images to
determine if more are needed.
Top
What will I
experience during the procedure?
You will feel pressure on the breast as it is squeezed
by the compressor. Some women with sensitive breasts
may experience discomfort. If this is the case, schedule
the procedure when your breasts are least tender. The
technologist will apply compression in gradations. Be
sure to inform the technologist if pain occurs as compression
is increased. If discomfort is significant, less compression
will be used.
Top
Who interprets
the results and how do I get them?
A radiologist, who is a physician experienced in mammography
and other x-ray examinations, will analyze the images,
describe any abnormalities, and suggest a likely diagnosis.
The report will be dictated by the radiologist, and
then sent to your referring physician. You will also
be notified of the results by the mammography facility.
This notification is usually sent a few days after the
official report goes to your doctor. New technology
also allows for distribution of diagnostic reports and
referral images over the Internet at some facilities.
Top
What are the
benefits vs. risks?
Benefits
Imaging of the breast improves a physician's ability
to detect small tumors. When cancers are small, the
woman has more treatment options, and a cure is more
likely.
The use of screening mammography increases the detection
of small abnormal tissue growths confined to the milk
ducts in the breast, called ductal carcinoma in situ
(DCIS). These early tumors cannot harm patients if they
are removed at this stage and mammography is the only
proven method to reliably detect these tumors.
Risks
The effective radiation dose from a mammogram is about
0.7 mSv, which is about the same as the average person
receives from background radiation in three months.
The Federal mammography guidelines require that each
unit be checked by a medical physicist each year to
insure that the unit operates correctly. See the Safety
page for more information about radiation dose.
Women should always inform their doctor or x-ray technologist
if there is any possibility that they are pregnant.
False Positive Mammograms. Five to 10 percent of screening
mammogram results are abnormal and require more testing
(more mammograms, fine needle aspiration, ultrasound
or biopsy), and most of the follow-up tests confirm
that no cancer was present. It is estimated that a woman
who has yearly mammograms between ages 40 and 49 would
have about a 30 percent chance of having a false-positive
mammogram at some point in that decade, and about a
7 to 8 percent chance of having a breast biopsy within
the 10-year period. The estimate for false-positive
mammograms is about 25 percent for women ages 50 or
older.
Top
What are the
limitations of Mammography?
Interpretations of mammograms can be difficult because
a normal breast can appear differently for each woman.
Also, the appearance of an image may be compromised
if there is powder or salve on the breasts or if you
have undergone breast surgery. Because some breast cancers
are hard to visualize, a radiologist may want to compare
the image to views from previous examinations. Not all
cancers of the breast can be seen on mammography.
Breast implants can also impede accurate mammogram
readings because both silicone and saline implants are
not transparent on x-rays and can block a clear view
of the tissues behind them, especially if the implant
has been placed in front of, rather than beneath, the
chest muscles. But the NCI says that experienced technologists
and radiologists know how to carefully compress the
breasts to improve the view without rupturing the implant.
When making an appointment for a mammogram, women with
implants should ask if the facility uses special techniques
designed to accommodate them. Before the mammogram is
taken, they should make sure the technologist is experienced
in performing mammography on patients with breast implants.
Top
Copyright © 2004 Radiological Society of North
America, Inc. (RSNA)
--------------------------------------------------------------------------------
What is Bone
Radiography?
Radiography, or an x-ray, as it is most commonly known,
is the oldest and most frequently used form of medical
imaging. Discovered more than a century ago, x-rays
can produce diagnostic images of the human body on film
or digitally on a computer screen.
X-ray imaging is the fastest and easiest way for a
physician to view and assess broken bones, such as skull
fractures and spine injuries. At least two images (from
different angles) are taken and often three images are
needed if the problem is around a joint (knee, elbow
or wrist). X-rays also play a key role in guiding orthopedic
surgery and in the treatment of sports-related injuries.
X-ray may uncover more advanced forms of cancer in bones,
although early screening for cancer findings requires
other methods.
To this end, radiologists have developed alternative
imaging methods that do not rely on radiation, such
as ultrasound and magnetic resonance imaging (MRI).
However, because x-ray was the first imaging modality,
many people (and medical imaging professionals) continue
to use the term "radiology" to include all
types of imaging. Strictly speaking, though, radiology
refers to the use of x-rays.
Top
What are some
common uses of the procedure?
Probably the most common use of bone radiographs is
to assist the physician in identifying and treating
fractures. X-ray images of the skull, spine, joints
and extremities are performed every minute of every
day in hospital emergency rooms, sports medicine centers,
orthopedic clinics and physician offices. Images of
the injury can show even very fine hairline fractures
or bone chips, while images produced after treatment
ensure that a fracture has been properly aligned and
stabilized for healing. Bone x-rays are essential tools
in orthopedic surgery, such as spinal repair, joint
replacements or fracture reductions.
X-ray images can be used to diagnose and monitor the
progression of degenerative diseases such as arthritis.
They also play an important role in the detection and
diagnosis of cancer, although usually computed tomography
(CT) or MRI is better at defining the extent and the
nature of a suspected cancer. On regular x-rays severe
osteoporosis can be visible, but bone density determination
for early loss of bone mineral is usually done on specialized,
more sensitive equipment.
Top
How should I
prepare for the procedure?
There is no special preparation required for most bone
radiographs. Once you arrive, you may be asked to change
into a gown before your examination. You will also be
asked to remove jewelry, eyeglasses and any metal objects
that could show up on the images and overlap important
findings. Women should always inform their doctor or
x-ray technologist if there is any possibility that
they are pregnant.
Top
What does the
x-ray equipment look like?
Radiography equipment consists of a large, flat table
with a drawer that holds a tray into which an x-ray
film cassette is placed. Suspended above the table is
the apparatus that holds the x-ray tube that can be
moved over the body to direct the x-ray.
An example of a typical piece of radiography equipment
is shown at the top of this page.
Top
How does the
procedure work?
Radiography involves exposing a part of the body to
a small dose of radiation to produce an image of the
internal organs. When x-rays penetrate the body, they
are absorbed in varying amounts by different tissues.
Ribs, for example, are dense and will block much of
the radiation and, therefore, appear white or light
gray on the image. Soft tissue such as the liver or
lungs will appear darker because more radiation can
pass through it to expose the film.
The images may be placed on film or may be stored electronically
on PACS (picture archiving and communication systems).
Films are usually stored in a film jacket in the radiology
department or in the doctor's office for approximately
seven years (unless the patient is a child, then until
age 21). Images may be digitally acquired or may be
digitized from analog images and can be stored on PACS.
Top
How is the procedure
performed?
The technologist positions the patient on the examination
table, places a film holder (cassette) under the table
in the area of the body to be imaged. Sandbags or pillows
may help the patient hold the proper position. Then
the technologist steps behind a radiation barrier and
asks the patient to hold very still without breathing
for a few seconds. The radiographic equipment is activated,
sending a beam of x-rays through the body to expose
the film. The technologist then repositions the patient
for another view, and the process is repeated.
When your x-rays are completed you will be asked to
wait until the technologist checks the images for adequate
exposure and motion.
Top
What will
I experience during the x-ray procedure?
X-ray imaging itself is painless. Some discomfort may
result from lying on the table, a hard surface that
may feel quite cold. Sometimes, to get a clear image
of an injury such as a possible fracture, you may be
asked to hold an uncomfortable position for a short
time. Any movement could blur the image and make it
necessary to repeat the procedure to get a useful, clear
picture.
Top
Who interprets
the results and how do I get them?
A radiologist is a physician experienced in bone x-ray
and all other types of radiology examinations. He or
she will analyze the images and send a signed report
to your primary care or referring physician, who will
inform you on your test results. New technology also
allows for distribution of diagnostic reports and referral
images over the Internet at many facilities.
Top
What are the
benefits vs. risks?
Benefits
X-ray imaging is useful to diagnose bone injury and
disease, such as fractures, bone infections, arthritis
and cancer.
Because x-ray imaging is fast and easy, it is particularly
useful in emergency diagnosis and treatment.
X-ray equipment is relatively inexpensive and widely
available in physician offices, ambulatory care centers,
nursing homes and other locations, making it convenient
for both patients and physicians.
Risks
X-rays are a type of invisible electromagnetic radiation
and create no sensation when they pass through the body.
Modern x-ray techniques use only a fraction of the x-ray
dose that was required in the early days of radiology.
Women should always inform their doctor or x-ray technologist
if there is any possibility that they are pregnant.
During a single x-ray exposure, a patient is exposed
to approximately 20 milliroentgens of radiation. To
put this into perspective, we are all exposed to approximately
100 milliroentgens of radiation each year from sources
like the ultraviolet rays of the sun and small traces
of radioactive isotopes, such as uranium found in soil.
Radiation risks are further minimized by:
The use of high-speed x-ray film that requires only
very small amounts of radiation to produce an optimal
image.
Technique standards established by national and international
guidelines that have been designed and are continually
reviewed by national and international radiology protection
councils.
Modern, state-of-the-art x-ray systems (including mammography
systems, angiographic equipment, labs and CT scanners)
that have very tightly controlled x-ray beams with significant
filtration and x-ray dose control methods. Scatter or
stray radiation is minimized and those parts of a patient’s
body not being imaged receive minimal exposure.
Top
What are the
limitations of Bone Radiography?
While x-ray images are among the clearest, most detailed
views of bone, they provide little information about
the adjacent soft tissues. In the case of a knee or
shoulder injury, for example, an MRI may be more useful
in identifying ligament tears, joint effusions or other
