such as movement in the intestinal track, or blood flow. It is real-time imaging. If a record
is needed, a “spot film” is taken. Some units can be equipped with a rapid film changer,
also called a “puck.” This unit allows for the quick sequencing of film during a procedure.
Some units can have a “multiformat” camera attached to them, in which case up to 32
images can be placed on one sheet of film. The same information that would be recorded
by the puck on many sheets of film is done electronically from the fluoroscopic image
received by the video system and is transmitted to the multiformat camera. Because the
image is captured by a video camera, it can be digitized and manipulated. This is sometimes
called “digital subtraction” or “digital subtraction imaging.” The fluoroscope works
at a lower power level than that required for the typical X-ray film. Therefore, if a film is
required, the system goes into “boost” mode to expose the film, and then automatically
drops back to its previous exposure level. Generally, patients receive a higher dose of radiation
during a fluoroscopic study than they would if only films were taken. Although the
power is lower, the exposure time is longer, thus giving the higher dosages of radiation.
Hanging from the sides of the I/I are strips of lead shielding, which must be inspected on
a regular basis for secure mounting and adequate coverage.
With the exception of C-arm units (see below), the X-ray tube is located under the table
on which the patient is positioned. The tube is in the same type of housing as previously
described. However, it does not rotate. The collimator is simpler as it has no targeting
light or cross hairs. After the X-ray beam passes through the patient, it is detected by the
image intensifier (I/I). At the back end of the I/I is a video camera that amplifies the light
generated by the X-rays striking the I/I and displays the light patterns on a CRT. That is
the simple explanation of a fluoroscope.
The I/I comes in various sizes, from 3 to 15 inches in diameter; 12- and 15-inch
units are not common in newer units as the radiation dose for these is high, and modern
techniques allow the radiologist to better target the areas being examined. Some units are