Microscopic visualization of high-frequency ultrasound fields using a newmethod of Schlieren photography

We have proposed a new technique for visualization of an ultrasound fieldthat enables acquisition of Schlieren images by subtraction of two shadowgraphstaken in the presence and absence of ultrasound exposure. This technique can beeasily applied to other optical methods because there is no need to use aconventional Schlieren optics. This paper shows the possibility of applying thetechnique to microscopic observation of high-frequency ultrasound fields. Alight source of short pulsed light of 0.11 ns and a CCD camera with a 15 bitdynamic range were installed in an inverted-type microscope. High-frequencyultrasound fields of a miniature 20-MHz transducer for intravascular ultrasoundimaging and a 50-MHz wideband transducer were visualized using 4 and 10objective lenses. Observation results showed that the high-frequency fields weresuccessfully visualized at the maximum spatial resolution of 0.93 m.Transmission and reflection of pulsed ultrasound at a water-Plexiglas interfacewere also observed, and the acquired movie image of ultrasound propagationdemonstrated the importance of this technique for direct understanding ofcomplex acoustic fields.