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CT
Scans (CBCT)
What
is CBCT?
To better
explain what Cone Beam CT ( CBCT ) is, we should
first explain what regular CT is:
Computed
tomography (CT) imaging, also referred to as a
computed axial tomography (CAT) scan, involves the
use of rotating x-ray equipment, combined with a
digital computer, to obtain images of the body.
Using CT imaging, cross sectional images of body
organs and tissues can be produced. Though there are
many other imaging techniques, CT imaging has the
unique ability to offer clear images of different
types of tissue. CT imaging can provide views of
soft tissue, bone, muscle, and blood vessels,
without sacrificing clarity. Other imaging
techniques are much more limited in the types of
images they can provide.
To understand the difference between CT imaging and
other techniques, consider an x-ray of the head.
Using basic x-ray techniques, the bone structures of
the skull can be viewed. With magnetic resonance
imaging (MRI), blood vessels and soft tissue can be
viewed, but clear, detailed images of bony
structures cannot be obtained. On the other hand,
x-ray angiography can provide a look at the blood
vessels of the head, but not soft tissue. CT imaging
of the head can provide clear images not only of
soft tissue, but also of bones and blood vessels.
CT imaging is
commonly used for diagnostic purposes. In fact, it
is a chief imaging method used in diagnosing a
variety of cancers, including those affecting the
lungs, pancreas, and liver. Using CT imaging, not
only can physicians confirm that tumors exist, but
they can also pinpoint their locations, accurately
measure the size of tumors, and determine whether or
not they’ve spread to neighboring tissues.
In addition to the diagnosis of certain cancers, CT
imaging is used for planning and administering
radiation cancer treatments, as well as for planning
certain types of surgeries. It is useful for guiding
biopsies and a range of other procedures categorized
as minimally invasive. Thanks to its ability to
provide clear images of bone, muscle, and blood
vessels, CT imaging is a valuable tool for the
diagnosis and treatment of musculoskeletal disorders
and injuries. It is often used to measure bone
mineral density and to detect injuries to internal
organs. CT imaging is even used for the diagnosis
and treatment of certain vascular diseases that,
undetected and untreated, have the potential to
cause renal failure, stroke, or death.
Watch the
video below for a better idea of how CT scanners
work:
|
Table 3.3
| Where
It's Done |
Who
Does It |
How
Long It Takes |
Discomfort/Pain |
| Hospital
radiology unit or outpatient diagnostic clinic. |
Radiologist
or technician. |
30-45
minutes. |
None
unless contrast medium is used; some people find
it uncomfortable to remain still during the test. |
| Results
Ready When |
Special
Equipment |
Risks/Complications |
Average
Cost |
| Often
in a few hours; may take longer in some cases and
other places. |
Revolving
CT scanner (camera), X-ray and computer equipment,
and monitor. |
Slight
risk from radiation exposure; use of contrast
agent (dye) can cause allergic reaction. |
£500.00 |
Other
names
Computed
axial tomograph (CAT) scans.
Purpose
- To
obtain a two-dimensional view of a cross section of
the brain or other internal organ.
- To
detect tumors, bleeding, and other abnormalities that
may not show up on an ordinary X-ray.
How it
works
- Multiple
X-rays are taken as the CT X-ray tube revolves around
the patient.
- A
computer calculates the amount of X-ray penetration
through the specific plane(s) of the body part(s)
examined, and gives each a numeric value (density
coefficient).
- This
information is fed into a computer, which translates
the values into different shades of gray.
- These
images are displayed on a television monitor and
photographed as a series of two-dimensional images
depicting a cross section of the part under
examination.
Preparation
- You will
be shown the CT machine and asked to express any
concerns.
- If you
experience claustrophobia in small, enclosed spaces,
you may be given a mild sedative to quell your
anxiety.
- If an
intravenous contrast agent is to be used, you will be
asked to abstain from ingesting food and water for at
least four hours beforehand.
- Before
entering the unit, you will be asked to remove any
jewelry or other objects that may interfere with clear
X-ray images.
Test
procedure
Variations
- CT
scanning may be performed in conjunction with other
imaging studies and diagnostic procedures, such as
X-rays of the joint or spinal column (eg, arthrography
or myelography). This allows more detailed images of
the entire joint structure than can be obtained from
X-rays alone.
- A
relatively new innovation is spiral CT imaging,
which allows for continuous scanning as the gantry
table slides through the unit. This technique cuts the
amount of time needed for whole-body scanning.
After
the test
- You may
be asked to wait while a radiologist quickly reviews
the images to make sure that the part of the body
under study has been adequately photographed.
- If
necessary, you may be asked to return to the scanner
for additional images. Otherwise, you will be able to
resume normal activities.
- If an
intravenous contrast medium was used, you will be
instructed to drink extra fluids to speed its removal
from the body.
- You
should also watch for delayed allergic reactions, such
as hives, a rash, itching, or perhaps a rapid
heartbeat. Such symptoms usually appear within two to
six hours; in severe cases, an antihistamine or
steroid medication may be prescribed to ease
discomfort.
Factors
affecting results
- Obesity,
movement during the examination, and the presence of
metallic objects can interfere with obtaining clear
images.
- In some
cases, excessive gas or fecal material in the
intestines can give misleading results in an abdominal
CT scan
Interpretation
A
radiologist will interpret the scans.
Advantages
- CT
scanning provides a painless, noninvasive method of
obtaining a detailed view of internal organs.
- In many
instances, CT scanning eliminates the need for more
invasive procedures
Disadvantages
- The test
is costly and may not be available in small hospitals
and rural areas.
- It is
contraindicated during pregnancy, and may not be
suitable for those who are very obese.
Based on The Yale University School
of Medicine Patient's Guide to Medical Tests by Barry L.
Zaret M.D., Senior Editor, Copyright (c) 1997 by Yale
University School of Medicine and G. S. Sharpe
Communications, Inc. Published under license from Houghton
Mifflin Company.
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