Optical and optoacoustic imaging in the diffusive regime

Optical imaging is capable of providing valuable molecular contrast, cell tracking, genetic reporters, and a wide range of biomarkers that reveal the biological processes underlying a disease. For centuries, optical imaging has primarily been confined to superficial tissue layers, due to the high scattering of photons in tissue. Optical tomographic methods based on accurate models of diffusive deep-tissue light propagation have allowed fluorescence and endogenous contrast to be visualized and volumetrically quantified at depths of centimeters. Emerging optoacoustic methods allow optical absorption contrast to be pinpointed at high spatial resolutions by means of ultrasound waves, breaking through the resolution limitations imposed by diffusive light. This chapter introduces the principles of optical and optoacoustic methods for imaging biomedically relevant contrast in the diffusive regime.