CT Head and Spine
What is the procedure?
CT (Computed Tomography, commonly called a Cat Scan) imaging uses a ring shaped x-ray detector to obtain x-ray images of the body at multiple angles around the body. Using complex mathematical reconstructions, a computer is then able to create a cross-sectional image (tomogram) of the body, much like a slice through the body. The computer generates multiple images, slices which could be stacked up to recreate the whole region scanned.
The interpreting radiologist then reviews the images at a digital workstation, dictating a report which is provided to the ordering physician.
What are some common uses for the procedure?
CT of the brain is commonly used for a head injury, headache, stroke, tumor evaluation,
and a CT can test for a wide array of neurologic symptoms such as dizziness,
seizures, etc. For many of these indications, additional evaluation may be
discussed with your physician.
How should I prepare for the procedure?
The procedure doesn't require any specific pre-procedural preparation.
What does the equipment look like?
The CT scanner is a ring of imaging equipment inside a square block-like housing which contains electronics, the x-ray generator and detectors, and the mechanical instrumentation to move the imaging components. The apparatus is relatively like a square doughnut. The patient lies on a cart or table which slides into the x-ray ring, but the ring is relatively thin and open at both ends so it should not present any problems for claustrophobic patients.
How is the procedure performed?
• Imaging is done with the patient lying on his/her back.
Motion obscures detail on the pictures, and so your cooperation will be necessary.
You will be asked to lie completely still. The technologist will be able to see
and hear you and also speak to you throughout the exam.
• The majority of brain and spine CT's do
not require contrast (x-ray dye) which is given intravenously. However, if
the exam is assessing certain questions, contrast may be utilized. If this
is necessary, an IV will be placed before the exam to allow injection, most
frequently in front of the elbow.
If contrast is used, this can normally cause
a warm flushing feeling through the body and a metallic taste in the mouth.
What should I expect during the procedure?
While the unit is scanning the images, the CT gantry rotates in a circle to allow
the x-ray tube to image from all angles. There is whirring and clicking in
the CT unit while the tube is rotating for the pictures. The table will slowly
slide through the ring to allow the machine to cover the necessary segment
of the body.
What are the benefits and risks?
Benefits:
CT evaluation of the brain and spine provides excellent evaluation of the anatomy of the brain and spine. In the brain, it is an excellent means to find evidence for injury, stroke, bleeding, masses, and a variety of other disorders. In the spine it provides excellent anatomical evaluation for fractures, some masses, some disk disease, and degenerative narrowings.
Risks:
For a head exam, the radiation dose for this exam is about 2mSv (milliSievert).
Over about 8 months, most people would get equivalent radiation exposure from
natural background radiation. Radiation exposure should be limited during pregnancy.
Allergic
reactions to contrast can occur, rarely severe ones. Trained physicians and
nurses with necessary medications and equipment will be available to treat
any reaction.
What are the limitations of the procedure?
CT
is not as good as MR in differentiating all soft tissue differences. Some
processes such as early stroke, or subtle masses may be difficult to distinguish,
particularly if they are along the brain base where there is more artifact
from the skull. In the spine, disk evaluation is less ideal than MR, and
the ability to distinguish processes within the cord is also limited.
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