Absorption of short laser pulses in a material gives rise to broadband ultrasound waves that are suitable for high resolution imaging. Two imaging modes are possible depending on whether the ultrasound is generated at the object surface or within the object. The former mode is usually called the laser ultrasound technique and yields images due to reflection of the wave at structures with acoustic mismatch to their surroundings. The latter mode is called photoacoustic imaging and is based on optical contrast because of the proportionality between optical absorption and generated pressure.
The general objective of the project was to design an imaging method for simultaneous ultrasound and photoacoustic imaging, using an array detector consisting of concentric rings, and to prove the applicability of this device for large depth of field imaging. Therefore the following steps were performed:
- Design of a ring detector array using fiber optic interferometers bent to circles.
- Design of a piezoelectric annual detector array.
- Develop methods for signal processing and synthetic aperture focusing techniques as well as deconvolution procedures for reduction of imaging artifacts.
- Design and testing of a scanning microscope based on the detector, ultrasound generation and signal processing technologies investigated in the previous steps.