DecodeSceneColorForMaterialNode replaced by Depth in SpiralBlur-SceneTexture

I want to replaced the scene color by depth in spiral blur scene texture, custom expression. The part of the code that i needs to replaced is
DecodeSceneColorForMaterialNode(NewUV);
I understand that is a built in function that show the scene color,
but a function like “DecodeDepthForMaterialNode(NewUV);” exist? Or it’s completly an other way to do this?
I want to do a function like a blur on a DepthFade node.

Thank you!