Photoacoustic Tomography: In Vivo Imaging from Organelles to Organs

Lights, Sound, Images Optical microscopy can readily image thin samples such as cells, but thicker samples, such as tissue, are more difficult to image directly, because of the multiple scattering of light. Wang and Hu (p. 1458 ) review methods for imaging biological samples on length scales ranging from organelles to whole organs that rely on the photoacoustic effect—the excitation of ultrasonic pressure waves when light is absorbed by molecules in solution. The incident light can be focused and scanned across a sample in a microscopy mode to create ultrasound images, or the entire region of interest can be illuminated and the ultrasound waves analyzed with a computer algorithm in a tomography mode. Imaging studies can reveal changes in oxygen metabolism and gene expression and in image biomarkers and vasculature.