1.2 Image Intensifier Light Output - CPI Indico 100 Series Service And Installation Manual

CPI Canada Inc.
3E.1.2 Image Intensifier Light Output
The following variables affect the transmitted light output of an I.I. tube.
•
Image Intensifier gain.
•
Field size - input to output.
•
System components.
•
Choice of X-ray techniques.
Image Intensifier Gain.
Image tube gain is affected by two different factors, the ratio of the input to output phosphor area and the
electron gain due to the electron acceleration from the cathode to anode. A third effect that slowly reduces
the I.I. tube's gain is age. The emissivity of the cesium cathode decays with time and usage.
Gain = Area of input divided by the area of the output multiplied by the energy of a photon
(E = hc/λ [where h = Plank's constant, c = speed of light and λ is the light wavelength])
Example: Consider the difference of I.I. tube gain when a 12 inch I.I. tube is switched between 6 inches
and 12 inches.
Gain with tube in NORMAL mode:
Gain =(6 X 6 X π)/(.5 X .5 x π) = 144 X E
Field Size - Input to Output.
Most modern I.I. tubes are the multi-mode type where the effective input area may be changed per the
nature of the procedure. To change the field size of an I.I. tube when a MAG mode is selected, the
electron beam over-scans the output target. This in effect reduces the ratio of input size to output size and
reduces the gain or light output of the I.I. tube.
Millenia / Indico 100 Series Service Manual
Gain with tube in the MAG mode:
Gain =(3 X 3 X π)/(.5 X .5 x π) = 36 X E
Figure 3E-2: I.I. input and output area
Ch # 740904-07
ABS Calibration
Rev. D
3E
Page 3E-3