Subject: What are the biological basics of a Scatchard plot ?

I am a ph-D student working at the interface between physics and biology. 
Indeed, I am develloping a probe for radio-imaging inside the brain for 
pharmacological purposes. When people do binding experiments in 
neuroscience they often use Scatchard plots to determine the receptors 
density and the dissociation constant of the studied reaction of binding
of a molecule to a receptor. Despite several trials I have not undertsood 
on which biological principles this method relies..could you help me ?
thanks....

Re: What are the biological basics of a Scatchard plot ?