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# SNR in X-ray imaging watch

1. The problem statement, all variables and given/known data
(1) An ideal digital detector only suffers from quantum noise. If, after being exposed to 5 µGy the mean pixel value in the image is 100 and the standard deviation of the pixel values in the image is 5, calculate the SNR?

The relationship between pixel value and detector dose is linear.

(2) What is the effect on SNR of applying a linear gain of factor 4 to increase all pixel values

Attempt at a solution

As I understand SNR = N/sqrt(N) so I would have said SNR = 10
But I don't understand why they gave the S.D value of 5...

Re part (2) I thought SNR was unaffected by gain as both noise and signal would increase by the same amount

Thanks for the help
2. (Original post by jsmith6131)
The problem statement, all variables and given/known data
(1) An ideal digital detector only suffers from quantum noise. If, after being exposed to 5 µGy the mean pixel value in the image is 100 and the standard deviation of the pixel values in the image is 5, calculate the SNR?

The relationship between pixel value and detector dose is linear.

(2) What is the effect on SNR of applying a linear gain of factor 4 to increase all pixel values

Attempt at a solution

As I understand SNR = N/sqrt(N) so I would have said SNR = 10
But I don't understand why they gave the S.D value of 5...

Re part (2) I thought SNR was unaffected by gain as both noise and signal would increase by the same amount

Thanks for the help
3. (Original post by uberteknik)
Ok so the answer is SNR = 20

Does gain have any effect on the overall SNR or does it affect S as much as N?
Thanks

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