High resolution nearfield measurements using optical diffraction tomography

The nearfield of the 10 MHz transducer is of special interest at our department as it influences the work in one of our projects to develop an ultrasound based blood perfusion measurement technique. Theory and measurements with 0.5 mm miniature hydrophones indicate that even higher spatial resolution is needed if the nearfield pattern is to be reconstructed correctly. Therefore, an optical method has been used. Optical Diffraction Tomography (ODT) combines light intensity measurements with tomography algorithms to produce a measurement system and is based on the Raman-Nath equations describing the interaction of light and ultrasound. Results from nearfield measurements of two different 10 MHz transducers show that the ODT-method can resolve the complex pattern.