A few science stories I had a hand in recently:
There’s a method called laser scanning fluorescence lifetime microscopy (FLIM) that looks good for peering into certain living tissues, but the fields of view possible have so far been tiny. German specialists Becker & Hickl have tweaked the technique so that it can scan an 18 millimeter area, which is much more like it.
Also: ultrasound is ubiquitous, but the various bits of electronics used in the kit itself can interfere with the subtle ultrasound signals you’re looking for. Using optical components rather than electronics and detecting the signals with a fibre-optics sensor would be better, and UCL has built an all-optical system efficient enough to be clinically useful.
And: heavy water is already used as a biological marker since it’s close enough to normal H2O that many metabolic processes can’t tell the difference. But to see it you need a mass spectrometer, which is big and expensive and not actually optical. Raman spectroscopy would be better and might be a way to photograph the exact boundaries of cancer tumors, a perennial problem—so perennial that the FLIM technology mentioned above is being put to the same use too.