The Rochester Diagnostic Center has already distinguished itself with
CORONARY ANGIOGRAPHY to detect CORONARY BLOCKAGES. This remarkable
achievement has positioned the RDC as 1 of few national centers performing this
procedure .
What are some common uses of the
procedure?
Because it provides detailed, cross-sectional views of all types of
tissue, CT is one of the best tools for studying the brain, chest, abdomen, and
pelvis. It is
often the preferred method for diagnosing many different cancers, including
lung, liver, and pancreatic cancer, since the image allows a physician to
confirm the presence of a tumor and to measure its size, precise location, and
the extent of the tumor's involvement with other nearby tissue. CT examinations
are often used to plan and properly administer radiation treatments for tumors,
and to guide biopsies and other minimally invasive procedures. CT can clearly
show even very small bones, as well as surrounding tissues such as muscle and
blood vessels. This makes it invaluable in diagnosing and treating spinal
problems and injuries to the hands, feet, and other skeletal structures. CT
images can also be used to measure bone mineral density for the detection of
osteoporosis. In cases of trauma, CT can quickly identify injuries to the liver,
spleen, kidneys, or other internal organs. Many dedicated shock-trauma centers
have a CT scanner in the trauma department. CT can also play a significant role
in the detection, diagnosis, and treatment of vascular diseases that can lead to
stroke, heart attack, gangrene or kidney failure.
The 3D CT allows for powerful reconstruction of body structures and volume
rendering. This makes techniques such as VOYAGES and FLY-
THROUGH possible. Voyages and Fly-through allow you to virtually
travel through blood vessels and body cavities, like the colon (virtual
colonoscopy) or the lungs (virtual bronchoscopy).
How should I prepare for the
procedure?
You should wear comfortable, loose-fitting clothing for your CT exam. Metal
objects can affect the image, so avoid clothing with zippers and snaps. You may
will also be asked to remove hairpins, jewelry, eyeglasses, hearing aids, and
any removable dental work, depending on the part of the body that is being
scanned. You may be asked not to eat or drink anything for one or more hours
before the exam. Women should always inform their doctor or x-ray technologist
if there is any possibility that they are pregnant.
How does the procedure work?
In many ways, CT scanning works very much like other
x-ray
examinations. Very small, controlled amounts of x-ray radiation are
passed through the body, and different tissues absorb radiation at different
rates. With plain radiology, when special film is exposed to the absorbed x-rays,
an image of the inside of the body is captured. With CT, the film is replaced by
an array of detectors, which measure the x-ray profile.
Inside the CT scanner is a rotating gantry that has an x-ray tube
mounted on one side and an arc-shaped detector mounted on the opposite side. An x-ray
beam is emitted in a fan shape as the rotating frame spins the x-ray
tube and detector around the patient. Each time the x-ray tube and
detector make a 360° rotation and the x-ray passes through the
patient's body, the image of a thin section is acquired. During each
rotation, the detector records about 1,000 images (profiles) of the expanded x-ray
beam. Each profile is then reconstructed by a dedicated computer into a
3-dimensional image of the section that was scanned.
The Aquilion 16 has an extremely rapid gantry rotation of 400 milliseconds.
It also slices down to 0.5 millimeters allowing for the most sensitive and rapid
imaging available today.
You might think of it like looking into a loaf of bread by cutting it into thin
slices. When the image slices are reassembled by computer, the result is a very
detailed, multidimensional view of the body's interior.
Spiral (helical) 3D CT has improved the accuracy of CT
for many diseases. A new vascular imaging technique - spiral CT angiography - is
noninvasive and less expensive than conventional angiography, and allows doctors
to see blood vessels without the need for more invasive procedures.
The term "spiral CT" comes from the shape of the path taken by the x-ray
beam during scanning. The examination table advances at a constant rate through
the scanner gantry while the x-ray tube rotates continuously around
the patient, tracing a spiral path through the patient. This spiral path gathers
continuous data with no gaps between images.
With spiral CT, refinements in detector technology support faster,
higher-quality image acquisition with less radiation exposure. It is
typically eight to 10 times faster than conventional CT. Such speed is
beneficial in all patients but especially in elderly, pediatric, or critically
ill patients, populations in which the length of scanning was often problematic.
A spiral scan can usually be obtained during A SINGLE BREATH HOLD
With conventional CT, small lesions may frequently go undetected when a patient
breathes differently on consecutive scans, as a lesion may be missed by unequal
spacing between scans. The speed of spiral scanning and single breath hold
increases the rate of lesion detection.
How is the procedure performed?
The technologist begins by positioning the patient on the CT table.
The patient's body may be supported by pillows to help hold it still and in the
proper position during the scan. As the study proceeds, the table will move
automatically into the CT scanner "doughnut." Depending on the area of the
body being examined, the increments of movement may be so small that they are
almost undetectable, or large enough that the patient feels the sensation of
motion.
A CT examination often requires the use of different contrast materials to
enhance the visibility of certain tissues or blood vessels. The contrast
material may be injected directly into the blood stream or swallowed depending on the type of examination.
Before scheduling the technologist will ask
whether the patient has any allergies, especially to medications or iodine, and
whether the patient has a history of diabetes, asthma, a heart condition, kidney
problems, or thyroid conditions. These conditions may indicate a higher risk of
reaction to the contrast material or potential problems eliminating the material
from the patient's system after the exam.
The Rochester Diagnostic Center uses only LOW OSMOLAR CONTRAST MEDIA
(LOCM). This is an expensive dye that has the least potential for allergic
reactions and the best profile for renal excretion (this means that it leaves
your body better than other dyes do).
For patients who need contrast for their examination and are known to have
allergic reactions to iodine, special precautions are taken to ensure their
safety and well-being prior, during, and after the exam.
A CT examination usually takes from fifteen minutes to half an hour. When the
exam is over, the patient may be asked to wait until the images are examined to
determine if more images are needed.
What will I experience during the
procedure?
CT scanning causes no pain, and with spiral CT, the need to lie still
for any length of time is reduced. For different parts of the body, the patient
preparation will be different. You may be asked to swallow a liquid contrast
material that allows the radiologist to better see the stomach, small bowel, and
colon. Some patients find the taste mildly unpleasant, but most can easily
tolerate it. For virtual colonoscopy, CO2
inflation will be used to minimize discomfort. You will experience a sense of abdominal
fullness, however, the
mild discomfort will not last long.
Commonly, a contrast material is injected into a vein to better define the blood
vessels and kidneys, and to accentuate the appearance between normal and
abnormal tissue in organs like the liver and spleen. Some people report feeling
a flush of heat and sometimes a metallic taste in the back of the mouth. These
sensations usually disappear within a minute or two. Some people experience a
mild itching sensation. If it persists or is accompanied by hives (small bumps
on the skin), the itch can be treated easily with medication. In very rare
cases, a patient may become short of breath or experience swelling in the throat
or other parts of the body. These can be indications of a more serious reaction
to the contrast material that should be treated promptly, so tell the
immediately if you experience these symptoms. Fortunately, with the safety of
the newest contrast materials, these adverse effects are very rare.
You will be alone in the room during the scan, however, the technologist can
see, hear, and speak with you at all times.
What are the limitations of CT
Scanning of the Body?
Very fine soft-tissue details in areas such as the knee or shoulder
can be more readily and clearly seen with MRI (magnetic resonance imaging). In
some situations, soft tissues may be obscured by nearby bone structures in a CT.
The exam is not generally indicated for pregnant women.
What are the benefits vs.
risks?
