FLUOROSCOPY PERFORMANCE

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.
Flux Gain = Number of Output Light Photon / Number of Input X-ray Photons

Minification Gain

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, then Brightness gain will be.
answer :

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

It is the ratio of the brightness (luminance, CD / m2) of the output phosphor and the 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.