3-12. METHOD OF INJECTION
Determined by the examiner, the injection may be made by the percutaneous
method or by the insertion of a needle, cannula, or catheter into a selected blood vessel
after surgical exposure and under local or general anesthesia. If a special injection
apparatus is used, the specialist should anticipate moving the apparatus into position,
checking out the electrical connections, disassembling and cleaning the apparatus after
usage, and similar tasks.
3-13. RATE OF INJECTION
Since time is an all-important factor, the rate of injection ties in with the need for
working out in advance signals or cues for making each desired exposure at the optimal
instant. For example, when a relatively large amount of contrast solution (usually of a
heavy concentration) is rapidly injected into the aorta, a delay of even one second in
making the exposure may render the projection valueless.
3-14. USE OF A TOURNIQUET
A tourniquet is used by many examiners, especially in examinations of the
extremities, to force the contrast agent into the deeper blood channels. The specialist
must be very careful while adjusting the position of the patient or exchanging cassettes
for serialized exposures to make sure that he does not disturb the tension of the applied
tourniquet or cause it to snap loose.
NOTE :
In some instances, an inflatable cuff may be used in lieu of the customary
rubber tubing.)
3-15. PROJECTIONS
The projections to be taken for any specific examination are determined by the
examiner, usually at the time the examination is begun. It is necessary for the specialist
to know:
a. What projections are to be made (for example: AP, lateral, oblique).
b. What area or areas are to be included in given projections.
c. Number of films to be exposed per projection and the time interval between
exposures.
d. How the patient is to be positioned for stereoscopic exposures, if indicated.
MD0959
3-16
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