be canceled through this bottle you get a very nice way from now you can see a very sharp image so that's the power of time reversal how do we implement the same concept in biological tissue we knew the guy star first of all to begin with which is really hard to do in tissue in the early days our field actually embedded some molecules into tissue that provides it guys that are the trouble is that's invasive you have to poke the tissue to you eject some dye or floor force and it's also not very flexible because once you have that