If we are all optically transparent, disease identification and treatment would be much easier. Unfortunately, biological tissues tend to be highly scattering in the optical domain, and so light cannot easily penetrate through our bodies the way x-ray can. Interestingly, light scattering is deterministic in nature and is therefore an entirely time-reversible process. I will discuss my group's work in employing this fact to perform deep tissue imaging. This work also opens up the possibility to do surgery without creating an incision opening and to perform targeted cancer optical therapy at large tissue depths.