fluoroscopy performance
The performance of the image intensifier tube increases with increasing illumination (brightness) of the image. This is due to multiplication of light photon on the output phosphor and image minification. Increase of illumination depends on the brightness gain of the tube. Hence the term brightness gain and conversion factor are used to assess the performance of the image intensifier tube.
Brightness gain
Brightness gain is the ratio of brightness to output phosphor and input phosphor. It depends on two cars.
Brightness gain = Flux gain X Minification Gain
Flux gain
The electrons are accelerated towards the anode due to the high variation between the photocathode and the anode. Which increases the light intensity on the output phosphor. The ratio of output screen light photon and input screen light photon is called Flux Gain. Its value is around 50.
Flux Gain = Number of Output Light Photon / Number of Input X-ray Photons
Minification gain
The light intensity increases when the size of the output phosphor image is reduced compared to the input phosphor image. This is called minification gain. This is equal to the square of the ratio of the size of the input and output screens.
Question: If d1 and d2 are 300mm and 30mm and II tube's Flux gain is 50 for an II tube respectively, then Brightness gain will be.
ans.
Flux Gain = 50
Minification gain = (d1/d2)2
= (300130)2
= 100
Brightness Gain = Flux gain X Minification gain
= 50 X 100
= 5000
Brightness gain is not a measurable quantity. Therefore, the conversion factor term is used to determine the performance of an II tube.
Conversion factor
This is the ratio of the output phosphor's brightness (luminance, CD / m2) and input x-ray exposure rate (𝛍Gy / sec). Its value is equal to 1% of brightenss gain. Its typical range is 50–300 (CD / m2) / (𝛍Gy / sec), and its corresponding brightness gain range is 5000–30000. The higher the brightness gain and conversion factor of an II tube, the more efficiency it has.
