microscopy techniques face the next challenge something I call diffusion limit right so they cannot go beyond one millimeter in depth in valid or tissue how do we overcome that problem so we use photo equipment rasca viewer in general photoacoustic tomography to overcome this problem where we actually use multiple scatter photons so I have a little cartoon here conventional microscopy use straight propagating photons the modern optical microscopy will tolerate a little bit of a scattering because they can be checked