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in a dicom image file WW and WC/WL are not included but VOI Lut tag is present and i want to calculate WW and WL from it

Vamsidhar B
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1 Answers1

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A VOI LUT is typically used for non-linear transformations of the pixel data, i.e. for transformations which can not be expressed by specifying WL/WW. For that reason, it is impossible to calculate WL/WW from VOI LUT.

[EDIT]: To be even more clear:

WL/WW is limited to linear transformations of the grayscales. So the difference between the mapped value of x and (x+1) is equal to the difference of the mapped value of y and (y+1).

This does not count for the VOI LUT module which was introduced to allow for non-linear transformations of the grayscales. That is, no assumptions can be taken about the correllation of mapped values (x, x+1), (y, y+1). VOI LUT can be used to define any weird curve for mapping gray values.

"any weird curve" can obviously not be approximated by a strictly linear function. For that reason, it is possible to express WL/WW by VOI LUT but not vice versa.

Markus Sabin
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  • Thanks for replying, But I want to know that how we can calculate WL/WL from VOI LUT – Vamsidhar B Jul 30 '19 at 09:51
  • you are welcome....and I am telling you that this (=calculating WW/WL from VOI LUT) is only going to work in very exceptional cases.WW/WC is LINEAR while VOI LUT is usually NON-LINEAR. – Markus Sabin Jul 30 '19 at 10:54