{HEAD ~ Perimeter receiver fiber optics/elements} are spaced apart from {TAIL ~ a central source} fiber optic/element and received light reflected from the surface of the object is measured 
{ HEAD ~ Perimeter receiver fiber optics / elements } are spaced apart from { TAIL ~ a central source } fiber optic / element and received light reflected from the surface of the object is measured
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH