Acoustic microscopy system: design and preliminary results

Abstract

An acoustic microscopy system was designed to perform 2D imaging in the C-plane with a single-element transducer. The ultrasound transducer was fabricated by polishing bulk lithium niobate (LiNbO 3) to the required thickness (approximately 60 or 45 μ) for the desired operating frequency (55 or 75 MHz). The polished LiNbO 3 was attached to acoustic backing and matching layers. Finally, an epoxy lens was applied and the transducer mounted in a housing. The transducer was mounted in a 3D motorized positioning stage and operated by a high-frequency pulser/receiver. Received echoes were sampled with a 2 GHz ADC card and displayed on a PC using software developed in the Matlab environment. Transducer frequency and bandwidth were measured off a steel plate positioned at the focal length. A penny was scanned initially to confirm expected performance before acquiring data from liver ( n=3) and spleen ( n=3) specimens. For the first probe, the peak frequency was 54.05 MHz with a −6 dB bandwidth of 6.76 MHz. The axial and lateral resolutions were estimated to be 114 and 188 μm, respectively. For the second probe, the peak frequency was measured to 82 MHz with a −6 dB bandwidth of approximately 23 MHz. The axial and lateral resolutions were estimated to be around 33 and 81 μm, respectively. C-scans of the penny clearly showed detailed structures on front and back, while the capsule and the trabecular structures of the splenic tissues could easily be separated in different layers. In conclusion, an acoustic microscopy system operating at 55–75 MHz has been constructed and the feasibility of obtaining high-resolution images of tissue specimens demonstrated.