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Compensation Principle I https://www.x-ray-forum.net/./22161106nx65772/compensation-principles-i-to-iii-f89/compensation-principle-i-t37.html |
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Author: | Klaus [ 04.11.2019, 21:26 ] |
Post subject: | Compensation Principle I |
The first compensation principle uses the fact, that in a digital image contrast is nearly never independed of noise. Compensation of reduced contrast by increased SNR If optimization of contrast cannot be achieved, the noise must be reduced (i.e., increased SNR). If contrast can be increased, there is more tolerance for higher noise (moderate or lower SNR can be used) Example: If the visibility of a 2-2T hole (Factor CNR/delta w -> difference of wallthickness ) is not given due to the limited contrast, there are several factors which could be used to get a sufficient image quality again. The SNRITotal could be increased with - longer exposure time (or more frames integrated in the PC), - higher tube current (if possible and would not spoil the focal spot) - higher keV (with the result in a lower µeff) - better detector with higher efficiency - better detector calibration. The µeff can be influenced with - lower kV setting (but mainly for the price of higher noise) - scatter protection (diaphragms in front of the tube) - screens and filters |
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