Acoustic impedance micro-imaging for biological tissue using a focused acoustic pulse with a frequency range up to 100 MHz

Abstract

We have proposed a new method for two-dimensional acoustic impedance imaging for biological tissue that can per- form micro-scale observation without slicing the specimen. A tissue was placed on a plastic plate of 0.5 mm in thickness. An acoustic pulse with a frequency range up to 100 MHz was trans- mitted from the rear side of the plate, the acoustic beam being focused at the boundary between the tissue and plate. The reflec- tion intensity was interpreted into local acoustic impedance of the target tissue. An acoustic impedance microscopy with 200 x 200 pixels, its field of view being 2 x 2 mm, was obtained by mechani- cally scanning the transducer. Quantification of acoustic imped- ance was performed using water or an appropriate material as a reference. The accuracy was evaluated using saline with various NaCl content. A rat cerebellum was employed as the specimen. The development of parallel fiber in cerebella cultures was clearly observed as the contrast in acoustic impedance. The pro- posed technique is believed to be a powerful tool for biological tissue characterization, as neither staining nor slicing is required.