A realtime 200 MHz ultrasound B-scan imager

The development of very high frequency ultrasound imaging systems affords a unique opportunity to visualize living tissue at the microscopic level. The objective of the work reported here is to implement a realtime B-scan imaging system operating at frequencies in the 100-200 MHz range with resolution approaching the size of single cells. The design and performance of special spherically focused lithium niobate transducers is described. These devices showed good sensitivity with insertion losses as low as -22 dB. Lateral and axial resolution of 12 and 22 microns respectively were measured at a centre frequency of 192 MHz with f-1.2 focusing. The design and signal processing aspects of the scanner are briefly described. Preliminary correlations of histopathology with in vitro images of human coronary arteries and are presented. The authors conclude that microscopic imaging of tissues in the 200 MHz range is feasible. The resulting images show great potential for the assessment of tissue microstructure.