What is the meaning of RescaleType = 'LOG_E REL' in a DICOM file?

Question

I am trying to figure out the meaning of RescaleType = 'LOG_E REL' in a DICOM file. To be more specific, I need to know how to process the raw pixel values to get the image displayed in a proper way. Up to now I have only seen files with RescaleType = 'P-VALUES', which seemed to be correctly processed when applying formula:

pixVal = rescaleIntercept + rescaleSlope * pixRaw.

What would be the rescaling formula to apply when RescaleType = 'LOG_E REL'?

Answer 1

I am not sure if this value is part of the Dicom standard or it is just a specific value for a given manufacturer.

I am telling that because I only have seen these values for the images generated by an old (currently out of service) Agfa ADC compact CR

In the documentation you can read this:

LOG_E REL: pixel values are linearly related to the Log Exposure on the image plate; the maximum pixel value corresponds to a delta LogE of 3.2767 above the LogE for the minimum pixel value; in this case, a VOI module (sequenced item) is present, also containing a lookup table. Only 12 bit is supported.

I do not know if you should apply a rescaling formula or this is just a note related to some kind of postprocessing algorithm having been applied to the original image.

I assume you should just apply the given VOI LUT instead of trying to apply a rescale equation.

Answer 2

It would help if you could share an example of such dataset. In any way, I believe this is a Type 3 tag in which case, the information is not really required. Just apply the Rescale Slope/Intercept as usual and see what it does.