What is a CT scan?
Computed tomography is commonly referred to as a CT scan. A
CT scan is a diagnostic imaging procedure that uses a combination of X-rays and
computer technology to produce images of the inside of the body. It 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 CT, 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 images possible.
CT scans may be performed to help diagnose tumors,
investigate internal bleeding, or check for other internal injuries or damage.
CT can also be used for a tissue or fluid biopsy.
Why are CT scans sometimes
ordered with contrast?
CT scans may be done with or without contrast. Contrast refers to a
substance taken by mouth or injected into an 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.
You will need to let your doctor know if you have ever had a reaction to
any contrast media 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.
How do I prepare for a CT scan?
If you are having a computed tomography angiography (CTA) or
a virtual colonoscopy, you will be given specific instructions when you make
your appointment.
PRECAUTIONS: If you are pregnant or think you may be pregnant, please check with your
doctor before scheduling the exam.
CLOTHING: You may be asked to change into a patient gown. If so, a gown will be
provided for you. Please remove all piercings and leave all jewelry and
valuables at home.
CONTRAST MEDIA: Contrast may be indicated for your exam. The contrast media
improves the radiologist’s ability to find structures that are abnormal and
understand normal anatomy better.
Some patients should not have an iodine-based contrast media.
If you have problems with your kidney function, please inform your radiologist
in advance. We may be able to perform the scan without the contrast media or
find an alternate imaging exam.
The most common type of CT scan with contrast is the
double-contrast study, which will require you to drink a contrast media before
your exam begins in addition to the IV contrast. The more contrast you are able
to drink, the better the images are for the radiologist to visualize your
digestive tract.
ALLERGY: Please inform the access center representative when you schedule your
scan if you have had an allergic reaction to any contrast media. IV contrast
will not be administered if you have had a severe or anaphylactic reaction to
any contrast media in the past. Mild to moderate reactions warrant a plan that
includes taking medication prior to the CT examination. These plans will be
discussed with you in detail when you schedule your exam. Any known reactions
to a contrast media should be discussed with your personal physician.
EAT/DRINK: If your study was ordered without contrast, you can eat, drink and take
your prescribed medications prior to your exam.
If your doctor orders a CT scan with contrast, do not eat
anything three hours prior to your CT scan. We encourage you to drink clear
liquids. You may also take your prescribed medications prior to your exam.
DIABETICS: People with diabetes should eat a light breakfast or lunch three hours
prior to the scan time. Depending on your oral medication for diabetes, you may
be asked to discontinue use of the medication for 48 hours after the CT
examination. Detailed instructions will be given following your examination.
MEDICATION: All patients can take their prescribed medications as usual.
What are the risks of a CT scan?
If you are pregnant or think you may be pregnant, you should
notify your health care provider.
The amount of radiation dose used in a CT scan is small. 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.
If you are claustrophobic or tend to become anxious easily,
tell your doctor ahead of time. You may be prescribed a mild sedative to take
before the procedure to make you more comfortable.
What happens during a CT scan?
CT scans may be performed on an outpatient basis or as part
of your stay in a hospital. Procedures may vary depending on your condition and
your physician’s practices. Generally, CT scans follow this process:
You may be asked to change into a patient gown. If so, a gown
will be provided for you. A locker will be provided to secure all personal
belongings. Please remove all piercings and leave all jewelry and valuables at
home.
If you are to have a procedure done with contrast, an IV line
will be started in the hand or arm for injection of the contrast media. For
oral contrast, you will be given a liquid contrast preparation to swallow. In
some situations, the contrast may be given rectally.
You will lie on a scan table that slides into a large,
circular opening of the scanning machine.
The technologist will be in another room where the scanner
controls are located. However, you will be in constant sight of the
technologist through a window. Speakers inside the scanner will enable the
technologist to communicate with and hear you. You may have a call button so
that you can let the technologist know if you have any problems during the
procedure. The technologist will be watching you at all times and will be in
constant communication.
As the scanner begins to rotate around you, X-rays will pass
through the body for short amounts of time. You will hear clicking sounds,
which are normal.
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 important that you remain very still during the
procedure. You may be asked to hold your breath at various times during the
procedure.
If contrast media is used for your procedure, you may feel
some effects when the contrast is injected into the IV line. These effects
include a flushing sensation, a salty or metallic taste in the mouth, a brief
headache, or nausea and/or vomiting. These effects usually last for a few
moments.
You should notify the technologist if you have any breathing
difficulties, sweating, numbness or heart palpitations.
When the procedure has been completed, you will be removed
from the scanner.
If an IV line was inserted for contrast administration, the
line will be removed.
While the CT procedure itself causes no pain, having to lie
still for the length of the procedure might cause some discomfort or pain,
particularly in the case of a recent injury or invasive procedure, such as
surgery. The technologist will use all possible comfort measures and complete
the procedure as quickly as possible to minimize any discomfort or pain.
What happens after a CT scan?
If contrast media was used during your procedure, you may be
monitored for a period of time for any side effects or reactions to the
contrast, such as itching, swelling, rash or difficulty breathing.
If you notice any pain, redness and/or swelling at the IV
site after you return home following your procedure, you should notify your
doctor, as this could indicate an infection or other type of reaction.
There is typically no special type of care required after a
CT scan. You may resume your usual diet and activities unless your doctor
advises you differently.
Your doctor may give you additional or alternate instructions
after the procedure, depending on your particular situation.
What are some of the advances in CT technology?
Advances in CT technology include:
High-resolution CT: This type of CT scan uses very thin
slices (less than 0.1 inches), which are effective in providing greater detail
in certain conditions, such as lung disease.
Helical or spiral CT: 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, providing more
detailed information. Multidetector-row helical CT scanners may be used to
obtain information about calcium buildup inside the coronary arteries of the
heart.
Ultrafast CT (also called electron beam CT): 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 buildup inside the
coronary arteries of the heart, but the helical scanners are much more common.
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 positron emission tomography and CT (PET/CT): The
combination of CT 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 that of PET to show cell function and metabolism in order
to offer greater accuracy in the diagnosis and treatment of certain types of
diseases, particularly cancer. PET/CT may also be used to evaluate conditions
such as epilepsy, Alzheimer’s disease and coronary artery disease.
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