the general approach describing the transfer properties of a transfer system is the method of measuring the DQE(f) according IEC 601223-1-2; the system under inspection could be the imaging system itself or a transfer system. Even a display system could characterized in that manner. If you do so you have to modify the methods described in the standard; but the mathematical approach would be the same.
By signal transfer property (STP) I mean the relationship between pixel value and air kerma. The relationship between pixel value and light level is standardised by the DICOM GSDF. So is the system STP masked by anatomical image processing, or does it affect the presentation of the final image?
Yes, thanks both. Interesting. I wouldn’t have thought windowing and display (provided DICOM calibrated monitor used) would be affecting the linearity of medical images differently. I think maybe my question is more simply, why are CR images log-scaled and DR images not?
The CR systems uses a log amplifier. There is one advantage as this roughly corrects the signal to be proportional to the density of everything in the beam i.e. inverting the effect of the exponential absorption properties. This is useful to know if you are looking at a raw clinical image (with linear LUT), it can be easier to view after applying a log transform to the images.
There is more and I am stretching my brain for this one, but there are some advantages in terms of noise for log amplifiers. I think linear amplifiers are used for DR as log amplifiers would amplify the electronic noise in low signal regions - this is not an issue for CR as there is negligible electronic noise.
Either way the images are generally presented to the reader with a sigmoid look up table.
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