Projection mode ultrasonic microscopy for cell-size observation

Ultrasonic microscope is a powerful tool for biological applications. This study is proposing new type of observation for internal structure of biological tissue without introducing contaminants. Glioma cells were cultured on a thin polystyrene film. The cultured space was subsequently enclosed between two films, with 15 μm in gap distance. A focused ultrasonic beam, its frequency range being 200-400 MHz was transmitted from the rear side of the film. Microscopic images were acquired by mechanically scanning the transducer. The acoustic impedance mode observes the direct reflection from the interface between the plastic substrate and specimen. It reflects acoustic property in the vicinity of the interface between the substrate and specimen. It is highly quantitative but does not perfectly reflect the internal structure. The Projection mode observes the reflection from the interface on the surface of the second substrate that is placed with a certain gap. The beam travels twice through the tissue and comes back. Internal structure can clearly be seen with this observation mode, but quantitative analysis will not be easy because the internal structure through the thickness is not perfectly uniform. In both modes observation can be performed without introducing any contaminant to the tissue system.