Visualizing and characterizing vascular structures is important for many areas of health care, from accessing difficult veins and arteries for laboratory testing, to diagnosis and treatment of cardiovascular disease. Photoacoustic (PA) imaging, one of the fastest growing fields of biomedical imaging, is well suited for this task. PA imaging is based on the photoacoustic effect, which starts with a pulsed laser source incident on biological tissue. If the wavelength of the source matches an absorption wavelength of a chromophore within the tissue, a portion of the pulse energy is absorbed by the chromophore and converted into heat. A subsequent increase in temperature, followed by an increase in pressure occurs. Acoustic waves are emitted when this pressure relaxes, which can be detected at the surface of the tissue. PA imaging is considered absorption based, therefore spectroscopic information can be extracted. Yet, unlike purely optical imaging techniques, multiple centimeters of depth can be imaged. Vascular structures, in particular, can be viewed with high contrast using PA imaging, because the absorption coefficient of blood is up to six orders of magnitude higher than surrounding tissues . Additional chromophores, such as lipids in atherosclerotic plaque, are beginning to be imaged using PA techniques in vitro .
This document was originally published by American Society of Mechanical Engineers in Journal of Medical Devices. Copyright restrictions may apply. DOI: 10.1115/1.4024483.
Johnson, Jami; Sabick, Michelle; and VanWijk, Kasper. (2013). "All-Optical Photoacoustic Detection of Absorbers in Tissue Phantoms". Journal of Medical Devices, 7(3), 030901-1 - 030901-2.