It is immensely useful to peer into the human body to determine someone’s health status.
Common medical imaging technologies include X-ray CT scans, which are good at detecting structures in hard tissue, and MRI, which is complementary and produces better images of soft tissue. Both rely on contrast to produce images.
Fluorescence emission is also useful for imaging, and fluorescent molecules can be engineered into almost any structure of biological interest. Such light-based detection is much more specific than contrast detection, but it suffers from the disadvantage that the emitted light is highly scattered and thus only visible when close to the surface. Very useful for cells in culture but not so good for whole organisms.
New work published in the Proceedings of the National Academy of Sciences may change this state of affairs (published online November 17, 2008). Niedre et al. image a mouse lung tumor containing fluorescent tags by observing only the emitted photons that pass straight through the animals without being scattered. This preserves the spatial information and allows the tumor to be observed more clearly and with higher definition.
The clever (and expensive) advance is to use very fast (femtosecond) light pulses and cameras sensitive enough to detect them, aka early photon tomography. In principle, any molecule of interest could be studied by attaching a suitable fluorescent probe, thus opening myriad possibilities for directly viewing cellular processes in living creatures.