Download How does the procedure work?

What is CT Scanning of the Head?
Computed tomography (CT), sometimes called CAT scan, uses special x-ray
equipment to obtain many images from different angles and then join them together to show a crosssection of body tissues and organs. CT scanning provides more detailed information on head injuries,
stroke, brain tumors and other brain diseases than do regular radiographs (plain x-ray films). It also
can show bone, soft tissues and blood vessels in the same images. CT of the head and brain is a
patient-friendly exam that involves radiation exposure.
What are some common uses of the procedure?
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Detection of bleeding, brain damage and skull fractures in patients with head injuries.
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Detecting a blood clot or bleeding within the brain shortly after a patient exhibits symptoms of
a stroke.
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Detection of stroke, especially with a new technique called Perfusion CT.
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Evaluation of the extent of bone and soft tissue damage in patients with facial trauma, and
planning surgical reconstruction.
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Detection of bleeding in a patient with a sudden severe headache who may have a ruptured or
leaking aneurysm.
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Detection of most brain tumors.
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Diagnosing diseases of the temporal bone on the side of the skull, which may be causing
hearing problems.
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Detection of enlarged brain cavities (ventricles) in patients with hydrocephalus.
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Determining whether inflammation or other changes are present in the paranasal sinuses.
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Planning radiation therapy for cancer of the brain or other tissues.
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Guiding the passage of a needle used to obtain a tissue sample (biopsy) from the brain.
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Non-invasive assessment of aneurysms or arteriovenous malformations through a technique
called CT angiography.
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Detecting diseases or malformations of the skull.
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Three-dimensional imaging of the skull and brain structures.
How should I prepare for the CAT scan?
You should wear comfortable, loose-fitting clothing for your CT exam. Anything that might interfere
with imaging of the head—such as earrings, eyeglasses, dentures, dental implants or hairpins—should
be removed.
No special preparation is needed for a CT scan of the head unless you are to receive a contrast
material—a substance that highlights the brain and its blood vessels and makes abnormalities easier to
see. If the radiologist believes that an intravenous (IV) injection of a contrast material will be helpful,
you may be asked in advance whether you have had allergies in the past or have ever had a serious
reaction to medication. CT scan contrast materials contain iodine, which can cause a reaction in
persons who are allergic. If you have known allergies to other medications it may raise the possibility
that you might have an allergic reaction to the contrast material. The radiologist also should know if
you have asthma, multiple myeloma or any disorder of the heart, kidneys or thyroid gland, or if you
have diabetes—particularly if you are taking Glucophage. Typically you will be asked to sign an
informed consent form before having CT with injection of a contrast material.
Women should always inform their doctor or x-ray technologist if there is any possibility that they are
pregnant. In some cases an alternate study will be performed to reduce or eliminate the radiation
exposure to the fetus.
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 of the center of the hole.
Within the machine, an x-ray tube on a rotating gantry (or frame) moves around the patient's body to
produce the images, making clicking and whirring noises as the arm moves. Though the technologist
will be able to see and speak to you, you will be alone in the room during the exam.
An example of the radiography equipment that may be used is shown above.
How does the procedure work?
Unlike conventional x-rays, which produce pictures of the shadows cast by body
structures of different density, CT scanning uses x-rays in a much different way. In CT of the head,
numerous x-ray beams are passed through the skull and brain at different angles, and special sensors
measure the amount of radiation absorbed by different tissues (and lesions such as a bleeding tumor).
As you lie still, the scanner parts revolve around you (although you cannot see this happen), emitting
and recording x-ray beams from as many as a thousand points on the circle. A special computer
program then uses the differences in x-ray absorption to form cross-sectional images, or "slices" of the
head and brain. These slices are called tomograms, hence the name "computed tomography."
How is the CAT scan performed?
CT scanning of the head may be performed in the hospital or at an outpatient radiology center, but in
either case your doctor must give you a written referral with the reason why the study should be
performed. You will lie on a table that is guided into the center of the scanner and you will be asked to
lie very still.
As stated earlier, some patients will require an injection of a contrast material 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. The contrast material will be injected through this line.
Depending on the number of images needed, a CT exam of the head and brain can take two to 20
minutes. When it is completed you will be asked to wait until the technologist examines the images to
determine if more are needed.
What is Mammography?
Mammography is a specific type of imaging that uses a low-dose x-ray system to examine breasts. A
mammography exam, called a mammogram, is used to aid in the diagnosis of breast diseases in
women.
An x-ray (radiograph) is a painless medical test that helps physicians diagnose and treat medical
conditions. Radiography involves exposing a part of the body to a small dose of ionizing radiation to
produce pictures of the inside of the body. X-rays are the oldest and most frequently used form of
medical imaging.
Two recent enhancements to traditional mammography include digital mammography and computeraided detection.
Digital mammography, also called full-field digital mammography (FFDM), is a mammography
system in which the x-ray film is replaced by solid-state detectors that convert x-rays into electrical
signals. These detectors are similar to those found in digital cameras. The electrical signals are used to
produce images of the breast that can be seen on a computer screen or printed on special film similar
to conventional mammograms. From the patient's point of view, digital mammography is essentially
the same as the screen-film system.
See "Full-Field Digital Mammography: A Potential Alternative to the Traditional Film-Screen
Technique?" under the News heading for more information on how FFDM works and its potential
advantages.
Computer-aided detection (CAD) systems use a digitized mammographic image that can be
obtained from either a conventional film mammogram or a digitally acquired mammogram. The
computer software then searches for abnormal areas of density, mass, or calcification that may
indicate the presence of cancer. The CAD system highlights these areas on the images, alerting the
radiologist to the need for further analysis.
What are some common uses of the procedure?
Mammograms are used as a screening tool to detect early breast cancer in women experiencing no
symptoms and to detect and diagnose breast disease in women experiencing symptoms such as a
lump, pain or nipple discharge.
Screening Mammogram
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. Research has shown that annual
mammograms lead to early detection of breast cancers, when they are most curable and breastconservation therapies are available.
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.
See the Breast Cancer page for information about breast cancer therapy.
Diagnostic Mammogram
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.
How should I prepare for a mammogram?
Before scheduling a mammogram, the American Cancer Society (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 for a mammogram 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 mammogram 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.
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 used exclusively for x-ray exams 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.
How does the procedure work?
X-rays are a form of radiation, like light or radio waves that can be focused into a beam. X-rays pass
through most objects, including the body. Once it is carefully aimed at the part of the body being
examined, an x-ray machine produces a small burst of radiation that passes through the body,
recording an image on photographic film or a special image recording plate.
Different parts of the body absorb the x-rays in varying degrees. Dense bone absorbs much of the
radiation while soft tissue, such as muscle, fat and organs, allow more of the x-rays to pass through
them. As a result, bones appear white on the x-ray, soft tissue shows up in shades of gray and air
appears black.
X-ray images are maintained as hard film copy (much like a photographic negative) or, more likely, as
a digital image that is stored electronically. These stored images are easily accessible and are
sometimes compared to current x-ray images for diagnosis and disease management.
How is the procedure performed?
Mammography is performed on an outpatient basis.
During mammography, a specially qualified radiologic technologist will position your breast in the
mammography unit. Your breast will be placed on a special platform and compressed with a paddle
(often made of clear Plexiglas or other plastic). The technologist will gradually compress your breast.
Breast
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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 stand behind a glass shield during the x-ray exposure. You will be asked to
change positions slightly between images. The routine views are a top-to-bottom view and an
oblique side view. The process will be repeated for the other breast.
The patient must hold very still and may be asked to keep from breathing for a few seconds while the
x-ray picture is taken to reduce the possibility of a blurred image. The technologist will walk behind a
wall or into the next room to activate the x-ray machine.
When the examination is complete, the patient will be asked to wait until the technologist determines
that the images are of high enough quality for the radiologist to read.
The examination process should take about 30 minutes.
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.
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.
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.
Examples of the radiography equipment that may be used are shown at the top of this page.
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 computerprocessed to form an image. In the body, protons are most abundant in the hydrogen atoms of
water—the "H" of H2O —so that an MR 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).
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 (usually gadolinium) 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.
What is Bone X-ray (Radiography)?
An x-ray (radiograph) is a painless medical test that helps physicians diagnose and treat medical
conditions. Radiography involves exposing a part of the body to a small dose of ionizing radiation to
produce pictures of the inside of the body. X-rays are the oldest and most frequently used form of
medical imaging.
A bone x-ray makes images of any bone in the body, including the hand, wrist, arm, foot, ankle, knee,
leg or spine.
What are some common uses of the procedure?
A bone x-ray is used to:
 determine whether a bone has been fractured or if a joint is dislocated.
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ensure that a fracture has been properly aligned and stabilized for healing following treatment.
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determine whether there is a build up of fluid in the joint or around a bone.
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guide orthopedic surgery, such as spinal repair, joint replacement and fracture reductions.
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evaluate injury or damage from conditions such as infection, arthritis, abnormal bone growths
or other bone diseases, such as osteoporosis.
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assist in the detection and diagnosis of cancer.
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locate foreign objects.
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evaluate changes in bones.
How should I prepare for the procedure?
Most bone x-rays require no special preparation.
You may be asked to remove some or all of your clothes and to wear a gown during the exam. You
may also be asked to remove jewelry, eye glasses and any metal objects or clothing that might
interfere with the x-ray images.
Women should always inform their physician or x-ray technologist if there is any possibility that they
are pregnant. Many imaging tests are not performed during pregnancy because radiation can be
harmful to the fetus. If an x-ray is necessary, precautions will be taken to minimize radiation exposure
to the baby.
What does the x-ray equipment look like?
The equipment typically used for bone x-rays consists of an x-ray tube suspended over a table on
which the patient lies. A drawer under the table holds the x-ray film or image recording plate.
A portable x-ray machine is a compact apparatus that can be taken to the patient in a hospital bed or
the emergency room. The x-ray tube is connected to a flexible arm that is extended over the patient
while an x-ray film holder or image recording plate is placed underneath.
How does the procedure work?
X-rays are a form of radiation, like light or radio waves that can be focused into a beam. X-rays pass
through most objects, including the body. Once it is carefully aimed at the part of the body being
examined, an x-ray machine produces a small burst of radiation that passes through the body,
recording an image on photographic film or a special image recording plate.
Different parts of the body absorb the x-rays in varying degrees. Dense bone absorbs much of the
radiation while soft tissue, such as muscle, fat and organs, allow more of the x-rays to pass through
them. As a result, bones appear white on the x-ray, soft tissue shows up in shades of gray and air
appears black.
X-ray images are maintained as hard film copy (much like a photographic negative) or, more likely, as
a digital image that is stored electronically. These stored images are easily accessible and are
sometimes compared to current x-ray images for diagnosis and disease management.
How is the procedure performed?
The technologist, an individual specially trained to perform radiology examinations, positions the
patient on the x-ray table and places the x-ray film holder or digital recording plate under the table in
the area of the body being imaged. When necessary, sandbags or pillows will be used to help the
patient hold the proper position. A lead apron may be placed over the patient's pelvic area to protect it
from radiation.
The patient must hold very still and may be asked to keep from breathing for a few seconds while the
x-ray picture is taken to reduce the possibility of a blurred image. The technologist will walk behind a
wall or into the next room to activate the x-ray machine.
The patient may be repositioned for another view and the process is repeated. At least two images
(from different angles) will be taken and often three images are needed if the problem is around a
joint (knee, elbow or wrist).
An x-ray may also be taken of the unaffected limb, or of a child's growth plate (where new bone is
forming), for comparison purposes.
When the examination is complete, the patient will be asked to wait until the technologist determines
that the images are of high enough quality for the radiologist to read.
A bone x-ray examination is usually completed within 5 to 10 minutes.
What is Abdominal Ultrasound Imaging?
Ultrasound imaging, also called ultrasound scanning or sonography, involves exposing part of the body
to high-frequency sound waves to produce pictures of the inside of the body. Ultrasound exams do not
use ionizing radiation (x-ray). Because ultrasound images are captured in real-time, they can show the
structure and movement of the body's internal organs, as well as blood flowing through blood vessels.
Ultrasound imaging is usually a painless medical test that helps physicians diagnose and treat medical
conditions.
An abdominal ultrasound produces a picture of the organs and other structures in the upper abdomen.
A Doppler ultrasound study may be part of an abdominal ultrasound examination.
Doppler ultrasound is a special ultrasound technique that evaluates blood as it flows through a blood
vessel, including the body's major arteries and veins in the abdomen, arms, legs and neck.
What are some common uses of the procedure?
Abdominal ultrasound imaging is performed to evaluate the:
 kidneys
 liver
 gallbladder
 pancreas
 spleen
 abdominal aorta and other blood vessels of the abdomen
Ultrasound is used to help diagnose a variety of conditions, such as:
 abdominal pains
 inflamed appendix
 enlarged abdominal organ
 stones in the gallbladder or kidney
 an aneurysm in the aorta
Other uses of abdominal ultrasound imaging include:
 guiding procedures such as needle biopsies in which needles are used to
extract a sample of cells from organs for laboratory testing.
 assisting in the assessment of damage caused by illness.
Doppler ultrasound images can help the physician to see and evaluate:
 blockages to blood flow (such as clots)
 narrowing of vessels (which may be caused by plaque)
 tumors and congenital malformation
How should I prepare for the procedure?
Ultrasound:
Gallbladder
Ultrasound:
Kidney
Ultrasound: Liver
You should wear comfortable, loose-fitting clothing for your ultrasound exam. You will need to remove
all clothing and jewelry in the area to be examined.
You may be asked to wear a gown during the procedure.
Tell your doctor if you have had a barium enema or a series of upper GI (gastrointestinal) tests within
the past two days. Barium that remains in the intestines can interfere with the ultrasound test.
Other preparations depend on the type of ultrasound you are having.
 For a study of the liver, gallbladder, spleen, and pancreas, you may be asked to eat a fat-free
meal on the evening before the test and then to avoid eating for eight to 12 hours before the
test.
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For ultrasound of the kidneys, you may be asked to drink four to six glasses of liquid about an
hour before the test to fill your bladder. You may be asked to avoid eating for eight to 12 hours
before the test to avoid gas buildup in the intestines.
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For ultrasound of the aorta, you may need to avoid eating for eight to 12 hours before the test.
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 that
resembles a microphone, attached to the scanner by a cord. The transducer sends out a high
frequency sound wave and then listens for a returning sound wave or "echo".
The ultrasound image is immediately visible on a nearby screen that looks much like a computer or
television monitor. The image is created based on the amplitude (strength), frequency and time it
takes for the sound signal to return from the patient to the transducer.
How does the procedure work?
Ultrasound imaging is based on the same principles involved in the sonar used by bats, ships and
fishermen. When a sound wave strikes an object, it bounces backward, or echoes. By measuring these
echo waves it is possible to determine how far away the object is and its size, shape, consistency
(whether the object is solid, filled with fluid, or both) and uniformity.
In medicine, ultrasound is used to detect changes in appearance and function of organs, tissues, or
abnormal masses, such as tumors.
In an ultrasound examination, a transducer both sends the sound waves and records the echoing
waves. When the transducer is pressed against the skin, it directs a stream of inaudible, highfrequency sound waves into the body. As the sound waves bounce off of internal organs, fluids and
tissues, the sensitive microphone in the transducer records tiny changes in the sound's pitch and
direction. These signature waves are instantly measured and displayed by a computer, which in turn
creates a real-time picture on the monitor. These live images are usually recorded on videotape and
one or more frames of the moving pictures are typically captured as still images.
Doppler ultrasound, a special application of ultrasound, measures the direction and speed of blood
cells as they move through vessels. The movement of blood cells causes a change in pitch of the
reflected sound waves (Doppler effect). A computer collects and processes the sounds and creates
graphs or pictures that represent the flow of blood through the blood vessels.
How is the procedure performed?
For most ultrasound exams, the patient is positioned lying face-up on an examination table that can be
tilted or moved.
A clear gel is applied to the area of the body being studied to help the transducer make secure contact
with the body and eliminate air pockets between the transducer and the skin. The sonographer
(ultrasound technologist) or radiologist then presses the transducer firmly against the skin and sweeps
it back and forth over the area of interest.
Doppler sonography is performed using the same transducer.
When the examination is complete, the patient may be asked to dress and wait while the ultrasound
images are reviewed. However, the sonographer or radiologist is often able to review the ultrasound
images in real-time as they are acquired and the patient can be released immediately.
This ultrasound examination is usually completed within 30 minutes.
What is CT Angiography?
CT (computed tomography) angiography (CTA) is an examination that uses x-rays to visualize blood
flow in arterial and venous vessels throughout the body, from arteries serving the brain to those
bringing blood to the lungs, kidneys, and arms and legs. CT combines the use of x-rays with
computerized analysis of the images. Beams of x-rays are passed from a rotating device through the
area of interest in the patient's body from several different angles to create cross-sectional images,
which then are assembled by computer into a three-dimensional picture of the area being studied.
Compared to catheter angiography, which involves placing a sizable catheter and injecting contrast
material into a large artery or vein, CTA is a much less invasive and more patient-friendly procedure—
contrast material is injected into a small peripheral vein by using a small needle or catheter. This type
of exam has been used to screen large numbers of individuals for arterial disease. Most patients
undergo CT angiography without being admitted to a hospital.
What are some common uses of the procedure?
CTA is commonly used to:
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Examine the pulmonary arteries in the lungs to rule out pulmonary embolism, a serious but
treatable condition.
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Visualize blood flow in the renal arteries (those supplying the kidneys) in patients with high
blood pressure and those suspected of having kidney disorders. Narrowing (stenosis) of a renal
artery is a cause of high blood pressure (hypertension) in some patients and can be corrected.
A special computerized method of viewing the images makes renal CT angiography a very
accurate examination. Also done in prospective kidney donors.
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Identify aneurysms in the aorta or in other major blood vessels. Aneurysms are diseased areas
of a weakened blood vessel wall that bulges out—like a bulge in a tire. Aneurysms are lifethreatening because they can rupture.
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Identify dissection in the aorta or its major branches. Dissection means that the layers of the
artery wall peel away from each other—like the layers of an onion. Dissection can cause pain
and can be life-threatening.
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Identify a small aneurysm or arteriovenous malformation inside the brain that can be lifethreatening.

Detect atherosclerotic disease that has narrowed the arteries to the legs.

Detect thrombosis (clots) in veins, for example large veins in the pelvis and legs. Such clots can
travel to the lungs and result in pulmonary embolism.
CTA is also used to detect narrowing or obstruction of arteries in the pelvis and in the carotid
arteries,which bring blood from the heart to the brain. When a stent has been placed to restore blood
flow in a diseased artery, CTA will show whether it is serving its purpose. Examining arteries in the
brain may help reach a correct diagnosis in patients who complain of headaches, dizziness, ringing in
the ears or fainting. Injured patients may benefit from CTA if there is a possibility that one or more
arteries have been damaged. In patients with a tumor, it may be helpful for the surgeon to know the
details of arteries feeding the growth.
How should I prepare for the procedure?
Depending on the part of the body to be examined, you may be asked to take only clear liquids by
mouth before CTA. You may be asked whether you have asthma or any allergies to foods or drugs,
and what medications you are currently taking. If you are pregnant, you should inform the
technologist before the procedure. You probably will not have to undress if you are undergoing an
exam of the head, neck, arms or legs but you will have to remove any jewelry, hair clips, dentures and
the like that could show up on the x-rays and make them hard to interpret.
What does the equipment look like?
A CT scanner is a specialized x-ray machine that looks like a large square doughnut. It has an opening
measuring about two feet in diameter that surrounds a narrow table. Inside the frame of the scanner
is a rotating device with an x-ray tube mounted on one side and a banana-shaped detector opposite it.
Nearly all CTA studies use an advanced type of unit called a spiral CT machine that looks like any other
type of CT unit, but is able to record a large number of pictures in a short time. This means that
patients do not have to hold their breath for a prolonged period.
An example of the CT equipment that may be used is shown above.
How does the procedure work?
Before the actual exam begins, you will have a dose of contrast material injected
into a vein to make the blood vessels stand out. An automatic injector machine is used that controls
the timing and rate of injection, which may continue during part of the time images are recorded.
During the examination, the rotating device spins around the patient, creating a fan-shaped beam of
x-rays, and the detector takes snapshots of the beam after it passes through the patient. As many as
one thousand of these pictures may be recorded in one turn of the detector. The real work of CTA
comes after the images are acquired, when powerful computer programs process the images and
make it possible to display them in different ways, for instance, in cross-sectional slices or as threedimensional "casts" of the blood vessels.
How is the procedure performed?
Most of the time for a CTA examination is spent setting everything up. Actually recording the images
takes only seconds. After changing into a hospital gown and having an IV set up, you will answer
questions about things that might complicate the exam (such as allergies), and then you will lie down
on a narrow table. The part of your body to be examined will be placed inside the opening of the CT
unit with the aid of criss-crossed positioning lights. A test image is taken to determine the best
position, and a small dose of contrast material may be given to see how long it takes to reach the area
under study. Then the IV is hooked up to an automatic injector, contrast material is injected, and the
scan begins. Afterward, the images will be reviewed and, if necessary, some will be repeated.