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Photoacoustic imaging is a new technique that uses sound rather than light to form detailed images of cells deep inside the tissues of living animals with no harmful side effects to them—in this case a mass of cells (in yellow) and associated blood vessels (in white) several millimeters under the skin of a living mouse. The improved resolution and depth of imaging achieved using this technique has many potential applications in medicine and biology, including the assessment of breast, skin and colon cancers, cardiovascular disease, and dermatological conditions in living animals at the cellular level.
To produce an image using photoacoustic imaging, nanosecond laser pulses are delivered to living tissue. The laser pulses generate high frequency ultrasound waves from different structures within the tissue. These ultrasound waves are related to the components of the tissue and are detected at the surface using a novel sensor. A detailed 3D image is then formed using a computer and a sophisticated image reconstruction algorithm based on the acoustic signal emitted by the tissue. In this example, photoacoustic images of genetically engineered tyrosinase-labelled K562 cells were imaged in mammalian tissues. The tyrosinase-labelled cells (colored yellow) are selectively visualized against the vasculature with high contrast at depths well beyond those achievable by in vivo light microscopy. The cell mass is approximately 6mm in diameter.
Paul Beard, PhD, Department of Medical Physics & Bioengineering, University College London, UK