- relatively low light-emission - this explains why there is low time-resolution (you need to integrate signals over minutes, no hope to have a millisecond resolution);
- scattering and absorption by tissues - this explains why there is low space-resolution (you get a planar image and no satisfactory 3D solutions have been made so far).
Probably these limitations less influence imaging of bright chemical probes (not reporter-genes) explaining some marketing decisions from Caliper. Or maybe, really this is a revolutionary machine with surprising performances even for reporter imaging. Let it be.