CT Scans 101: Be an Informed Consumer
HealthSmart! CT Scans 101: Be an Informed Consumer (Printable PDF, 166 KB)
CT (computerized tomography) scans, also
sometimes called CAT scans, combine X-rays
and computers to produce remarkably clear
images of many parts of the body. Sometimes
compared to slicing a loaf of bread (but with
no knife, of course!), the CT scanner can
peek inside your head, neck, chest, abdomen,
arms or legs in search of injury or disease.
CT scans provide much finer detail than
regular X-rays, evaluating organs that can’t
even be seen with X-rays. And because the
scanning process is so quick, CT is especially
useful for patients who have been injured,
such as in traffic accidents or falls. When
there are complex bone injuries, such as hip
fractures for example, the CT images can be
combined into a lifelike three-dimensional
view to provide the surgeon with a virtual
roadmap for making repairs.
But CT’s contributions aren’t limited to
patients who’ve been injured. It also is
a primary tool for finding tumors nearly
everywhere in the body. After it reveals
the tumor, repeat CT scans are used for
evaluating whether the tumor is responding
to therapy. Exciting new uses are being
found for CT scanning, such as checking
arteries (including the ones in the heart) for
What CT scans can show
CT isn’t perfect. It doesn’t find every
disease in every patient. But it can detect
many different types of illness and injury
• Internal bleeding in the brain or body
• Bone fractures and dislocations
• Kidney stones
• Blocked arteries and veins
• Congenital heart diseases
MRI vs. PET/CT
MRI – Instead of using X-rays to create
images of the body, MRI uses magnets and
CT vs. MRI – Sometimes, either CT or MRI
would be an option for a patient’s particular
situation. In other cases, one examination
would be preferred over the other. Searching
for brain tumors, for example, is better
handled with MRI, while checking for blood
clots in the lung is a job for CT. Your doctor
and the imaging specialist reading your scan
can tailor the examination to find the best
answer for you. MRI scans take longer to
do, sometimes require long periods without
moving, and can be a problem for very sick
or young patients or those with a fear of
small, tight places. CT can provide a rapid
alternative if MRI scanning isn’t possible.
PET/CT – PET stands for positron emission
tomography. This test can show how tissues and
organs in the body are working, rather than just
how they look.
A tiny dose of radioactive material called a tracer
is injected into an arm vein and is taken up by
organs throughout the body. The tracer gives off
a low dose of radiation that can be detected by a
scanner surrounding the patient. Body tissues that
are using a lot of energy, such as tumors, take up
more of the tracer, and the scanner detects that
abnormal activity. Sometimes this can be referred
to as a “hot spot.”
Images from a CT scan performed at the same
time then are combined with the PET scan to form
a 3-D view that shows exactly where in the body
the abnormality is.
How is a PET/CT different from a CT or MRI scan?
CT and MRI scans are great for showing normal
and abnormal anatomy but can’t always tell
whether something is benign or malignant – just
an old scar or a living tumor, for example. Often,
PET/CT can help to answer that question. In
patients being treated for a known cancer, PET/CT
can be a great way to see if the therapy is working
and to search for any spread of the tumor.
Radiation exposure: Risky or not?
Radiation exposure should be a concern
for everyone, and it certainly is for us at UK
HealthCare. We want our patients to receive the
lowest possible radiation dose in all of our testing.
But some questions remain: Can this radiation be
harmful? Might it cause cancer years from now?
How much radiation is too much?
Any radiation is too much if you really don’t
need the test. When your doctor prescribes an
examination involving radiation, it’s perfectly
acceptable to express your concern about
radiation, to ask what they hope to learn from the
test, and to ask whether other non-radiation tests
could be used instead.
While the radiation risk from a single scan is quite
small, the radiation dose from multiple X-ray tests
over a lifetime can be significant. Patients with
chronic illnesses such as cancer or Crohn’s disease
are the ones most likely to have multiple scans.
But every patient should take common-sense steps
to protect themselves from excess radiation:
• Keep a record of any test that involves radiation.
If you’re unsure whether the test uses radiation,
ask the person who is performing it.
• Carry the record with you. Keep and update a
wallet-size card listing the imaging tests that
you’ve had and where and when each was done.
Many patients now keep the record electronically.
• If and when your doctor advises you to have a
test that uses radiation, express your concern and
ask a lot of questions. In particular, ask whether
a test that doesn’t use radiation could provide the
• Be aware of dosages. After your CT scan, ask the
person who performed it what dose of radiation
you received. Include that information in your
UK HealthCare employs a radiation safety officer
(RSO) who ensures that all activities involving
radioactive materials and all tests using equipment
that produce radiation are performed in accordance
with approved policies and regulatory requirements.
Frequent testing is done to ensure that the
equipment and procedures are up to standards. The
radiation safety officer is authorized to prohibit
use of any equipment that does not meet safety
and quality guidelines as defined by UK HealthCare
policies and federal and state regulations.
“You are more likely to
die being struck by a car,
drowning, or by radon in your
home than from cancer caused
by the radiation of a CT scan.”
–Scott D. Stevens, MD, Chief, Abdominal Imaging, UK Radiology
Radiation exposure comparison
Humans have always lived in a radioactive world – we
are exposed to natural sources of radiation constantly.
Soil, rocks, building materials, air, water and cosmic
radiation emit small amounts of “background
radiation” all the time. If you think of the very low dose
of radiation from a standard chest X-ray as equaling 1,
then background radiation would equal about 30. Just
living in the United States gives you as much radiation
in a year as 30 chest X-rays.
So how does CT imaging compare to background
radiation? The table on the right presents the average
relative radiation dose-per-person for a variety of
sources – both medical and non-medical.*
Will you get the lowest possible dose?
Companies that manufacture CT equipment know that
you and your doctor want the best-quality scan with
the lowest radiation dose. To achieve that goal here
at UK HealthCare, we use a dose-reduction system.
During your CT scan, a computer in the CT scanner
will analyze each body section to make sure that it gets
only enough radiation to get a clear view. For example,
it takes a lot less radiation to see through your lungs
than to look inside your liver, and so our system
adjusts the radiation dose during your scan to make
sure that’s what happens. We’re especially proud of
how our system can reduce radiation exposure for our
Is iodinated contrast (X-ray dye) safe?
Iodinated contrasts are particularly safe
medications that have been used for many
years with few serious side effects. Because
iodinated contrast can increase the diagnostic
usefulness of a CT scan, its benefits are
considered to outweigh the low risk.
The most common effect of iodinated contrast
is a warm or “flushed” feeling during the
actual injection, sometimes with a metallic
taste, that typically lasts for less than a
minute. This sensation is expected and needs
Another mild reaction is itching or “hives”
over various parts of the body that can last
from minutes to hours. Medications are
available to help relieve the itch.
Very rarely, more significant side effects such
as low blood pressure or difficulty breathing
can occur shortly after contrast injection.
Radiology department personnel will observe
you during and for a short time after your
scan to be certain that you’ve had no problem.
Even more rarely, delayed side effects,
particularly rashes, can appear several hours
after your scan. If you experience anything
unusual, call your doctor or visit a hospital
emergency department and mention that
you’ve recently received intravenous contrast
for a CT scan.
It is important for patients to notify their
physician and CT technologist if they have
had prior contrast reactions. On the rare
occasions, when patients experience delayed
side effects, they should phone their physician
or visit an emergency care provider.
CT is particularly useful...
• When a very detailed image of bone or
blood vessels is needed.
• In emergency situations, when
scanning has to be quick.
• When a patient would have difficulty
• In patients with pacemakers or certain
• During some image-guided procedures,
such as needle biopsies.
* The doses are typical values for an average-size
adult. The actual dose can vary significantly,
depending on the patient’s size and other variables.
Typically, your doctor will order a CT scan to
evaluate a particular problem, and the imaging
physician will then tailor the scan to answer
the specific question. If the problem could be
better evaluated with a different test, the imaging
specialist might call your doctor to discuss other
options. Before your scan begins, you’ll be asked to
provide information about your medical history and
any previous experience with X-ray contrast (“dye”).
Preparation for a CT scan depends upon which part
of the body is being scanned. You might be asked to
remove clothing and wear a hospital gown. Metal
objects, such as jewelry, should be removed so as
to not interfere with the image results. Additionally,
certain dietary restrictions might be necessary,
such as no food or drink for a certain period of time
before the examination. Be certain your doctor is
aware of all current medications you are taking
before you undergo a scan. Certain medications
may need to be stopped and others may be given
prior to scanning.
Patients having a CT scan often are asked to drink
a flavored liquid, or to receive an intravenous
injection into their arm. These contrast materials
(“X-ray dye”) highlight abnormalities on the CT scan
so that they are more apparent. In some cases, a CT
scan can still provide valuable information without
the administration of a contrast agent.
Contrast material can be introduced into the
body in different ways:
By mouth – Fruit-flavored liquid contrast is very
safe, and passes through the intestinal tract like
regular food or drink. Side effects are uncommon.
Temporary diarrhea occurs occasionally, and very
rarely patients can be allergic to the iodine or
flavoring in the drink.
Intravenous injection – Some patients describe a
warm “flushed” sensation or a metallic taste as the
contrast is being injected. These sensations typically
last only a few moments and are not dangerous.
Rectal – Contrast material occasionally is
administered into the rectum to evaluate colon and
rectal abnormalities. Patients often experience a full
sensation and more rarely cramping. A restroom is
available nearby so the contrast can be eliminated
promptly at the end of the examination.
Skill of the CT technologists
CT technologists have had specific training in
performing these scans, and their education
includes anatomy and physiology, radiation physics
and safety training. In order to become certified,
they must pass an examination that tests their
knowledge and skill. At UK HealthCare, our CT
technologists are accredited by the American
Registry of Radiologic Technologists, ensuring
expertise and professionalism in their area of care.
During the scan: What to expect
A CT scan is painless, but does require lying still and
sometimes short periods of breath-holding. Patients
with claustrophobia or difficulty remaining still may
benefit from a mild sedative given before the scan.
Women should always inform their
physician and CT technologist if there is
any possibility that they could be or are
pregnant. CT scanning is, in general, not
recommended for pregnant women, unless
specifically necessary, because of potential
risk to the fetus. Nursing mothers should
follow their doctor’s advice on how long to
wait after contrast material injection before
The scanner is shaped like a large doughnut with
a table running through it. After you lie down, the
table will move to the correct position for scanning
the specific body part. Expect occasional clicking
and buzzing sounds as the machine revolves during
the actual scanning process. Although patients
typically are alone in the examination room during
the scan, the radiology technologist will be able to
see, hear and speak with you at all times, so that any
discomfort or problem can be attended to promptly.
At the conclusion of the scan, the technologist
will check the images to be certain that they are
adequate. Afterward, you can go on about your day
as usual. If the scan included contrast material by
mouth or intravenously, drinking plenty of fluids
is recommended. You can return to your usual
schedule of medications as soon as your scan is
After the scan
Your CT scan will be interpreted by a doctor
specially trained in reading advanced X-ray studies.
At UK HealthCare, these imaging specialists
typically have undergone additional training
to become experts at reading specific types of
scans, such as brain, chest, heart, abdomen and
extremities. This makes them particularly well
qualified to handle complex cases.
CT Scans and Children
Image Gently is an educational and awareness
campaign created by the Alliance for Radiation
Safety in Pediatric Imaging. Its goal is to provide
safe, high-quality pediatric imaging nationwide.
The coalition represents more than 500,000 health
care professionals in radiology, pediatrics, medical
physics and radiation safety.
The Image Gently campaign promotes optimal
scanning strategies for children:
• Image only when there is a clear medical benefit.
• Use the lowest amount of radiation possible.
• Image only the indicated area.
• Avoid multiple scans.
• Use non-radiation studies (such as ultrasound or
MRI) when possible.
UK HealthCare is proud to apply the Image Gently
principles to better serve our youngest patients, but importantly, also applies this model to our adult
patients as well.
UK HealthCare CT
UK HealthCare houses eight CT scanners,
performing well over 5,000 examinations
each month. These versatile machines
accommodate patients from newborns to
650 pound adults.
Our CT resources include scanners that
acquire 64 or 40 “slices” at once, CT
fluoroscopy for guidance during biopsies,
and a dual energy scanner with exciting
prospects for kidney stones and heart
CT scan appointments are scheduled in
15-minute time slots.
A special concern for pediatric CT scanning:
How to keep the little ones still
Just as in adult CT scans, having a patient who
doesn’t move is critical to obtaining the best quality
scan for a child. Technologists use a variety of
age-appropriate methods that help children hold
still during a CT scan. Below is a list of the most
common ways children are kept still:
• Sandbags: Long sandbags can keep a child’s arms
or legs still and correctly positioned and act as a
reminder not to move.
• Velcro straps: Velcro bands not only immobilize
the child’s body, but also prevent them from falling
off the table. The straps are attached to the table
and are drawn snugly over the body.
• Swaddling: Infants and very young children
might be wrapped tightly in a blanket. While some
children are annoyed by the confinement, others
are comforted by the security and even fall asleep.
• Holding techniques: At times, a child may be
gently held by radiologic staff to keep a limb or
body part in the correct position. If parents are
asked to help hold their child, the staff will give
you specific instructions so that safe radiation
practices are observed.
What you can do to help
• Children may be upset or sense parental
• Be sure to speak calmly and firmly to
reassure your child.
• Praise him or her for being cooperative and
helping the CT technologist.
• Feel free to ask if you can remain in the room
during the test. If so, radiation safety
equipment will be provided.
UK HealthCare Radiology
UK HealthCare Radiology offers a full
range of state-of-the-art diagnostic imaging
services for patients. We conduct imaging of
patients at multiple sites. Please visit http://ukhealthcare.uky.edu/services/radiology.htm for more information.
Patient Appointments: 859-323-9977
American College of Radiology
1891 Preston White Drive
Reston VA 20191
This health care professional membership
group is dedicated to making imaging safe,
effective and accessible to those who need it.
American Society of Radiologic Technologists
15000 Central Ave. SE
Albuquerque NM 87123-3909
www.asrt.org The mission of the American
Society of Radiologic Technologists is to advance
the medical imaging and radiation therapy
profession and to enhance the quality of patient
MedlinePlus (CT Scans)
HealthFinder (CT Scan)
National Cancer Institute (Computed Tomography:
Questions and Answers)
• Advances & Insights: Can noninvasive
CT scans replace conventional coronary
• Advances & Insights: Studies examine
radiation exposure, long-term cancer risks of