ABSTRACT
This chapter shows that a double-ring sensor can be used to image blood vessels in vivo. Applications include the estimation of vessel size, detection of venous valves, and monitoring tumor growth. The double-ring sensor has an extremely narrow angular aperture and by applying dynamic focusing, an infinite depth-of-focus can be obtained. Photoacoustic imaging with a narrow angular aperture sensor such as the double-ring sensor is less sensitive to motion artifacts compared to imaging with large angular aperture sensors. Photoacoustic imaging with large angular aperture sensors requires reconstruction algorithms to obtain an image, and accordingly the image blurs when motion artifacts occur during imaging. For sensors with a narrow angular aperture, the time traces can be regarded as one-dimensional (1D) depth images of photoacoustic sources inside the measurement volume. The directivity pattern of a sensor can be estimated by laterally displacing the sensor with respect to a photoacoustic point source.
