A 100-200 MHz ultrasound biomicroscope

The development of higher frequency ultrasound imaging systems affords a un ique opportunity to visualize living tissue at the microscopic level. This work was undertaken to assess the potential of ultrasound imaging in vivo u sing the 100-200 MHz range. Spherically focused lithium niobate transducers were fabricated. The properties of a 200 MHz center frequency device are d escribed in detail. This transducer showed good sensitivity with an inserti on loss of 18 dB at 200 MHz;. Resolution of 14 mum in the lateral direction and 12 mum in the axial direction was achieved with f/1.14 focusing. A lin ear mechanical scan system and a scan converter were used to generate B-sca n images at a frame rate up to 12 frames per second. System performance in B-mode imaging is limited by frequency dependent attenuation in tissues. An alternative technique, zone-focus image collection, was investigated to ex tend depth of field. Images of coronary arteries, the eye, and skin are pre sented along with some preliminary correlations with histology. These resul ts demonstrate the feasibility of ultrasound biomicroscopy in the 100-200 M Hz range. Further development of ultrasound backscatter imaging at frequenc ies up to and above 200 MHz will contribute valuable information about tiss ue microstructure.