Professor Michael C. Kolios
Canada Research Chair in Biomedical Applications of Ultrasound Department of Physics Ryerson University
Ultrasound imaging is one of the most commonly used imaging modalities worldwide. Ultrasound imaging is similar in principle to radar detection; a pulse of radio waves (pressure waves for ultrasound) is transmitted and a detection system detects a small part of the wave’s energy that is reflected from the structures of interest. However, it has also been known that absorbed electromagnetic energy (such as light) can be used to generate sound - Alexander Graham Bell showed that absorbed energy from light causes heating and due to thermal expansion a pressure wave (sound) is generated. This phenomenon forms the basis of photoacoustic spectroscopy and imaging. In photoacoustic imaging, a short burst of electromagnetic energy is typically used to create transient thermoelastic expansion of absorbing structures and therefore wideband acoustic emissions (in the ultrasonic range: from MHz to GHz). To detect these photoacoustic pressure waves, conventional ultrasound detection technology can be used. Images that represent spatial maps of optical absorption can be formed. In this presentation, the physics of photoacoustic imaging will be introduced, and biomedical applications presented. In particular, we will examine how information from the wideband photoacoustic signals can be used to image and characterize objects from the mm scale (using MHz ultrasound detectors) to the micron scale (using GHz ultrasound detectors). Applications in small animal imaging as well as clinical imaging will also be presented.
