WHAT IS CAT SCAN?
CT scan is a non-invasive exam that combines the principles of x-ray
with advanced computer technology to produce precise cross-sectional
views of the internal organs and structures of the body. A 360 degree
x-ray beam and computer production of images are used to create â€œslicesâ€
of the body and create a more three-dimensional picture than a
traditional x-ray. CT scan is more comprehensive and detailed than
conventional x-ray as it enables the body to be viewed slice by slice,
from all angles rather than as a snapshot or photograph. A CT scan is
used to define normal and abnormal structures in the body and/or assist
in procedures by helping to accurately guide the placement of
instruments and treatments. Since CT provides detailed information in a
short period of time, it is often the imaging modality of choice in
CAN I HAVE A CAT SCAN? WHAT ARE THE RISKS?
The following may affect you being able to have a CT scan:
- Known or possible pregnancy
- Barium used for another test. These substances show up on a CT
scan. If a CT scan of your belly is needed, it should be done before
any tests that use barium.
- You are not able to lie still during the exam.
- Metal objects in the body, such as surgical slips or metal in
joint replacements, may prevent a clear view of the area of
A CT scan is a very safe study. Although CT exams require the use of
ionizing radiation (x-ray) and there is a slight risk from x-ray
radiation exposure, the amount of radiation used is minimized by
advanced CT detectors and computer technology to achieve the best image
quality at the lowest possible radiation dose. Also, protective
shielding is used routinely to prevent unnecessary radiation exposure.
For CT examinations performed WITHOUT intravenous contrast, there is
no risk involved in the exam unless you are or may be pregnant. The
risks and benefits of having the CT scan should then be discussed with
your doctor to determine the best course of action.
For CT examinations performed WITH intravenous iodinated contrast,
most patients have no reaction or side effects. However, as with most
diagnostically beneficial medical examinations, there are certain risks.
The risks are related to allergic and non-allergic reactions to the
Minor reactions to the IV contrast used for CT scan may include
nausea, vomiting, headache or dizziness, which are usually of short
duration and usually require no treatment. Sometimes there are cases of
hives (urticaria) and rash, which we can treat with antihistamines or
other medications. Rarely, asthma can be induced, which is also
More serious reactions to the IV contrast used for CT scan, such as
blood clotting, kidney damage, inflammation of a vein (phlebitis), shock
and fatal reactions have occurred but only rarely. The incidence of
fatal reaction is less than 1 in 100,000 patients receiving IV contrast
with iodine, which is much less than reactions to many antibiotics and
other medications used daily in medical practice.
If you would like more information or have any questions about the
use of IV contrast, the CT staff and/or radiologist will speak with you
at the time of your appointment. Also, please see the â€œif contrast is
used sectionâ€ for further information regarding the use of IV contrast.
If you are breastfeeding and receive IV contrast, you will need to
use formula for 2 days after your CT scan so that you do not pass the
dye to your baby. You should throw out any breast milk you collect
during this time.
HOW DOES IT WORK?
The CT scanner is a large doughnut-shaped machine. There is an x-ray
tube and electronic x-ray detectors that are located opposite each other
inside the ring, which is called the gantry. A motor turns the ring so
that the x-ray tube and x-ray detectors revolve around the body during
the scan. You will lie on a narrow, moveable table that will slide you
through the ring into the center of the CT machine. Once inside the
scanner, numerous x-ray beams rotate around you at many different angles
as the small detectors inside the scanner measure the amount of
radiation that makes it through the part of the body being studied. The
computer uses this information, along with advanced mathematical
algorithms, to create several individual images called â€œslices,â€ which
can be stacked to create a three-dimensional image of the body. A
computer workstation that processes the imaging information is located
in the next room where the technologist operates the scanner and
monitors the exam.
PREPARATION FOR YOUR CT SCAN
For all patients having a CT scan:
- You may take all medications on your usual schedule as directed
by your doctor.
- Please bring a list of all of your current medications.
All CT scans with IV contrast:
1. Your physician will order a lab test to check your creatinine
level before the test. Since the kidneys filter out the IV contrast
after the exam, it is important to have this lab test so that we know if
your kidneys are working properly. This bloodwork must be done at least
two days before the exam. If a creatinine result from a test that has
been performed within one month of the appointment date is available,
new labwork is not needed.
2. Do no eat or drink anything for 4 hours prior to the exam.
CT scan of the abdomen/pelvis:
1. Pick up drinks in the x-ray department at least one day prior to
your appointment, along with the instructions on what time to drink the
2. Do not eat or drink anything for 4 hours prior to the exam.
3. If this exam has been ordered with IV contrast, please follow above
instructions for required labwork.
Any other CT examination requires no additional preparation.
WHEN TO ARRIVE/WHAT TO EXPECT WHEN YOU DO
You should arrive 10 minutes before your appointment time and report to
the Radiology front desk area at the Landmark campus where you will be
checked in. You will wait in the main Radiology waiting room where you
will be greeted by a CT technologist who will bring you back to the CT
scan area. The technologist will interview you to obtain medical
history, as well as explain the exam and answer any questions that you
may have prior to performing the exam. You may have to wear a gown
depending on the area of the body being scanned.
WHAT TO EXPECT DURING THE CAT SCAN
- The technologist will position you on the table for best quality
images. You will be lying on your back and may have to raise your
arms above your head.
- You will have to lie flat and very still for the entire exam as
movement reduces the quality of the images.
- You may be asked to hold your breath briefly as pictures are
taken during the scan.
- The technologist will watch you from the room next door and will
communicate with you via intercom.
- If you feel uncomfortable or need assistance at any point, the
technologist is readily available to assist you.
- If intravenous contrast is used, you will be injected. At the
time of injection, you may have a brief feeling of warmth and
flushing, a salty or metallic taste in your mouth or feel the urge
to urinate. This feeling should not last. If you feel any other
symptoms such as itching, headache, dizziness, difficulty breathing,
nausea and/or vomiting please inform the technologist immediately.
- Depending on the type of machine and the area(s) of interest,
the exam may take up to 30 minutes.
IF INTRAVENOUS CONTRAST IS USED
Contrast may sometime be needed to highlight your organs, blood vessels
or tissues and to help make normal and abnormal structures more visible.
Its use improves the radiologistâ€™s ability to make a detailed and
correct diagnosis of disease processes or injury and/or to provide
reassurance that nothing at all is wrong with the part of the body being
The contrast that is used for CT exams is called Isovue. It contains
iodine. Most patients will feel a warm sensation during or after the
injection, but will have no reaction or side effects. However, there is
a risk of reaction to the IV contrast. Please see the section entitled
â€œCan I have a Cat scan? What are the risks?â€ for further information.
If your CT exam requires IV contrast, you will be screened by the
technologist for the following conditions/diseases before any contrast
- A previous adverse reaction to contrast media
- A history of asthma or allergies
- Allergy to any medications, iodine dye or foods (especially
- Heart condition/dysfunction
- Pulmonary hypertension
- Kidney disease
- Diabetes and/or are taking Metformin (Glucophage)
- Sickle cell disease
- Multiple myeloma
At the time of your appointment, the technologist will answer any
questions you may have about the use of intravenous contrast prior to
injection and you will be required to sign a consent form.
Our equipment is serviced regularly to ensure your safety, and
our technologists are highly skilled and extremely knowledgeable. Also,
our professional CT staff will interview you thoroughly prior to the
exam and fill out a comprehensive history sheet relating to both your
past medical history and your present symptoms. If there are any
contraindications, the scan will not be performed. If your specific CT
exam requires you to have IV contrast, the risks will be explained to
you prior to the administration of any contrast and you must sign a
consent form. In the event of a reaction to the IV contrast, our
radiologists and staff will respond and treat the reaction immediately
and monitor your symptoms closely.
WHAT TO EXPECT AFTER THE CAT SCAN
There are no side effects, after-effects or restrictions after the exam.
You may perform all regular activities and may take all medications,
except Metformin (Glucophage) if you had a CT scan with IV contrast.
Please see the next section â€œSpecial Instructions for Diabetic Patients
If you had a CT scan with IV contrast, you should drink extra fluids
to help remove the contrast from your body.
SPECIAL INSTRUCTIONS FOR DIABETIC PATIENTS ON METFORMIN
Metformin is a drug commonly used to treat diabetes and control blood
Metformin has a variety of brand names including the following:
- Glucophage or Glucophage XR
- Actoplus Met or Actoplus Met XR
In a few instances, the combination of Metformin and the IV contrast
(x-ray dye) can cause a rare condition known as lactic acidosis. Please
follow these special instructions to prevent this problem from
If you are on any of the above medications and you have had a CT scan
with IV contrast, you will be informed by the CT staff to stop taking it
immediately after your CT scan, and you should not take this medication
for two days after the CT scan. Your doctor will also be notified of
this. The radiologist will give you a prescription ordering another lab
test to re-check your creatinine level (kidney function) before you can
start taking Metformin again. You will need to call your doctor for the
results of the blood test and to find out when to resume taking
WHAT ABOUT THE RESULTS
Our radiologists will read the exam within 24 hours. If your
physician requests a STAT reading, it will be provided to them via phone
call and/or fax immediately following your exam. The results will also
be available via internet as soon as the final report is dictated by the
radiologist. A copy of the final report will be forwarded to the
ordering physician and/or primary care physician who will discuss the
results with you.