CT, also known as CAT scanning, is an advanced x-ray
system that generates detailed cross-sectional images of the
body. Each image provides the visual equivalent of a
bloodless slice of the anatomy. When stacked together, these
slices create detailed studies of the organs as well as the
head, spine, chest, abdomen, and many other areas of the body.
CT scans can be done even if you have a pacemaker or aneurysm
clip -- devices implanted in your chest to help regulate your
heartbeat. However, if you're pregnant or suspect you might be,
tell your doctor. Your doctor may suggest postponing the
procedure or choose an alternative exam that doesn't involve
radiation, such as an ultrasound or MRI.
Before Your CT Scan
Some CT scans are enhanced by the use of IV or oral contrast.
If your exam requires contrast, you should not eat anything for
six hours prior to your appointment. In addition, please
refrain from drinking anything within an hour of your exam. You
may be asked to wear a gown during your exam and you will need
to remove all jewelry, dentures, hearing aids, etc., that might
interfere with the scan.
Time Required for Your CT Scan
CT exams generally last 15-30 minutes, however, if your scan
requires you to drink oral contrast prior to your exam, you
will be asked to arrive 1 hour prior to your scheduled
Who Performs Your CT Scan
An ARRT Certified Radiologic technologist will perform the exam
During Your CT Scan
As the scan begins, you will hear a slight whirring sound from
the CT machine. The technologist will position you on a table
within the scanner's doughnut-shaped ring, which will move you
through the machine for the exam. To produce the clearest
images possible, please lie still throughout the exam and
follow the breathing instructions given by your technologist
over the intercom.
After Your CT Scan
You may be asked to wait for a short time after your exam while
the radiologist reviews all the scans to ensure that the needed
information has been obtained. Occasionally, repeat or
additional scans are required. Once it is determined that your
exam is complete, you may leave. The radiologist will send a
report to your physician, typically within 48 hours. If IV or
oral contrast was used during your scan it is best to drink
plenty of fluids afterward to help eliminate it from your body.
Radiation Safety & CT Scans
Adventist Medical Center and Gresham Imaging Center are
committed to providing excellent image quality in order to
ensure accurate diagnoses. We also adhere to best medical
practice guidelines by minimizing the radiation dose to each
and every patient. The concept known as ALARA (as low as
reasonably achievable) is employed to guide the balance between
image quality and dose.
Computed Tomography (CT or CAT) Scan
What is a CT or CAT scan?
A CT or CAT scan is a diagnostic imaging procedure that uses
a combination of X-rays and computer technology to produce
horizontal, or axial, images (often called slices) of the
body. A CT scan shows detailed images of any part of the
body, including the bones, muscles, fat, organs, and blood
vessels. CT scans are more detailed than standard X-rays.
In standard X-rays, a beam of energy is aimed at the body
part being studied. A plate behind the body part captures the
variations of the energy beam after it passes through skin,
bone, muscle, and other tissue. While much information can be
obtained from a regular X-ray, a lot of detail about internal
organs and other structures is not available.
In computed tomography, the X-ray beam moves in a circle
around the body. This allows many different views of the same
organ or structure, and provides much greater detail. The
X-ray information is sent to a computer that interprets the
X-ray data and displays it in two-dimensional form on a
monitor. Newer technology and computer software makes
three-dimensional (3-D) images possible.
CT scans may be done with or without contrast. "Contrast"
refers to a substance taken by mouth or injected into an
intravenous (IV) line that causes the particular organ or
tissue under study to be seen more clearly. Contrast
examinations may require you to fast for a certain period of
time before the procedure. Your doctor will notify you of
this prior to the procedure.
CT scans may be performed to help diagnose tumors,
investigate internal bleeding, or check for other internal
injuries or damage.
You may want to ask your doctor about the amount of radiation
used during the CT procedure and the risks related to your
particular situation. It is a good idea to keep a record of
your past history of radiation exposure, such as previous CT
scans and other types of X-rays, so that you can inform your
doctor. Risks associated with radiation exposure may be
related to the cumulative number of X-ray examinations and/or
treatments over a long period of time. If you are pregnant or
suspect that you may be pregnant, you should notify your
Advances in computed tomography technology include the
High-resolution computed tomography. This type of CT scan
uses very thin slices (less than one-tenth of an inch),
which are effective in providing greater detail in
certain conditions such as lung disease.
Helical or spiral computed tomography. During this type
of CT scan, both the patient and the X-ray beam move
continuously, with the X-ray beam circling the patient.
The images are obtained much more quickly than with
standard CT scans. The resulting images have greater
resolution and contrast, thus providing more detailed
information. Multidetector row helical CT scanners may be
used to obtain information about calcium build-up inside
the coronary arteries of the heart.
Ultrafast computed tomography (also called electron beam
computed tomography). This type of CT scan produces
images very rapidly, thus creating a type of "movie" of
moving parts of the body, such as the chambers and valves
of the heart. This scan may also be used to obtain
information about calcium build-up inside the coronary
arteries of the heart, but the helical scanners are much
Computed tomographic angiography (CTA). Angiography (or
arteriography) is an X-ray image of the blood vessels. A
CT angiogram uses CT technology rather than standard
X-rays or fluoroscopy to obtain images of blood vessels,
for example, the coronary arteries of the heart.
Combined computed tomography and positron emission
tomography (PET/CT). The combination of computed
tomography and positron emission tomography technologies
into a single machine is referred to as PET/CT. PET/CT
combines the ability of CT to provide detailed anatomy
with the ability of PET to show cell function and
metabolism to offer greater accuracy in the diagnosis and
treatment of certain types of diseases, particularly
cancer. PET/CT may also be used to evaluate epilepsy,
Alzheimer's disease, and coronary artery disease.
Studies show that 85 percent of the population will not
experience an adverse reaction from iodinated contrast;
however, you will need to let your doctor know if you have
ever had a reaction to any contrast dye, and/or any kidney
problems. A reported seafood allergy is not considered to be
a contraindication for iodinated contrast. If you have any
medical conditions or recent illnesses, inform your doctor.
The effects of kidney disease and contrast agents have
attracted increased attention over the last decade, as
patients with kidney disease are more prone to kidney damage
after contrast exposure. If you are pregnant or think you may
be pregnant, you should notify your health care provider. If
you are claustrophobic or tend to become anxious easily, tell
your doctor ahead of time, as he or she may prescribe a mild
sedative for you before the procedure to make you more
comfortable. It will be necessary for you to remain still and
quiet during the procedure, which may last 10 to 20 minutes.
How is a CT or CAT scan performed?
CT scans can be performed on an outpatient basis, unless they
are part of a patient's inpatient care. Although each
facility may have specific protocols in place, generally, CT
scans follow this process:
When the patient arrives for the CT scan, he or she will
be asked to remove any clothing, jewelry, or other
objects that may interfere with the scan.
If the patient will be having a procedure done with
contrast, an intravenous (IV) line will be started in the
hand or arm for injection of the contrast medication. For
oral contrast, the patient will be given the contrast
material to swallow.
The patient will lie on a scan table that slides into a
large, circular opening of the scanning machine.
The CT staff will be in another room where the scanner
controls are located. However, the patient will be in
constant sight of the staff through a window. Speakers
inside the scanner will enable the staff to communicate
with and hear the patient. The patient may have a call
bell so that he or she can let the staff know if he or
she has any problems during the procedure.
As the scanner rotates around the patient, X-rays will
pass through the body for short amounts of time. The
motion is hidden inside the gantry, the doughnut-shaped
part of the machine. The patient may hear buzzing,
whirring, and clicking as the X-ray tube rotates.
The X-rays absorbed by the body's tissues will be
detected by the scanner and transmitted to the computer.
The computer will transform the information into an image
to be interpreted by the radiologist.
It is very important that the patient remain very still
during the procedure. You may be asked to hold your
breath at various times during the procedure.
The technologist will be watching the patient at all
times and will be in constant communication.
The patient may be asked to wait for a short period of
time while the radiologist examines the scans to make
sure they are clear. If the scans are not clear enough to
obtain adequate information, the patient may need to have
additional scans performed.