d. Kilovoltage and Milliamperage. These factors depend on the size and
density of the subject under examination and on the level of image brightness desired.
Kilovoltages ranging from 70 to 120 kVp at an x-ray current of 1/2 to 2 mA are
commonly used. Insufficient current (mA), especially when high kVp is used, may
cause the image to lack definition and appear grainy. When this image is viewed in
motion, a coarse, mottling effect is apparent. This is the result of scintillation or
"quantum noise," and it occurs when the level of x-radiation falls below a given
minimum. In other words, there is a level of radiation below which an image of good
quality cannot be obtained. The quantum noise in the intensified image is inversely
proportional to the number of x-ray photons absorbed in the fluorescent layer of the
input phosphor within the integration time of the human eye, which is approximately 0.2
seconds.
NOTE :
During fluoroscopy, the radiation dose necessary to create an image must be
delivered during the integration or recognition time of the eye, while during
cinefluorography, the radiation required to create the image must be delivered
during the exposure time for each frame of the motion picture.
1-16. DUTIES AND RESPONSIBILITIES OF THE X-RAY SPECIALIST
a. The x-ray specialist's duties and responsibilities in the performance of image-
intensified fluoroscopy and cinefluorography are much the same as for conventional
fluoroscopy for the other procedures. Radiation hazards do exist and the x-ray
specialist must be just as careful to take the same precautions as for ordinary
fluoroscopy.
b. To function efficiently as a member of the team, he must have a practical
understanding of the equipment and their uses and of the technical mechanics of the
procedure. For this reason, the x-ray specialist who is to assist in image-intensification
work should study the manual of instructions for the particular unit, as well as any other
available literature. With this knowledge, he will be better prepared to carry out the
radiologist's orders.
a. Density equalization filters are special accessory devices used when it is
desirable to cause a variation of x-ray intensity across a given beam. When the filter is
introduced into the path of the x-ray beam, its intensity is modified in differing degrees
over given portions of the file being irradiated (figure 1-7). This is achieved by selective
absorption.
MD0959
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