Radiodensity
Radiodensity ( or radiopacity ) is opacity to the radio wave and X-ray portion of the electromagnetic spectrum: that is , the relative inability of those kinds of electromagnetic radiation to pass through a particular material . 
<triplet> radio wave <subj> electromagnetic spectrum <obj> part of <triplet> X-ray <subj> electromagnetic spectrum <obj> part of <subj> electromagnetic radiation <obj> instance of