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.
Abstract
Photoacoustic tomography (PAT) can create multiscale multicontrast images of living biological structures ranging from organelles to organs. This emerging technology overcomes the high degree of scattering of optical photons in biological tissue by making use of the photoacoustic effect. Light absorption by molecules creates a thermally induced pressure jump that launches ultrasonic waves, which are received by acoustic detectors to form images. Different implementations of PAT allow the spatial resolution to be scaled with the desired imaging depth in tissue while a high depth-to-resolution ratio is maintained. As a rule of thumb, the achievable spatial resolution is on the order of 1/200 of the desired imaging depth, which can reach up to 7 centimeters. PAT provides anatomical, functional, metabolic, molecular, and genetic contrasts of vasculature, hemodynamics, oxygen metabolism, biomarkers, and gene expression. We review the state of the art of PAT for both biological and clinical studies and discuss future prospects.
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Published In
Science
Volume 335 | Issue 6075
23 March 2012
23 March 2012
Copyright
Copyright © 2012, American Association for the Advancement of Science.
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Published in print: 23 March 2012
Acknowledgments
We thank J. Ballard for close reading of the manuscript, and J. Yao for providing Fig. 3H. Supported by NIH grants R01 EB000712, R01 EB008085, R01 CA134539, U54 CA136398, R01 CA157277, R01 EB010049, and R01 CA159959. L.V.W. has financial interests in Microphotoacoustics Inc. and Endra Inc., which, however, did not support this work.
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