title: High-frequency ultrasound annular array imaging. Part II: digital beamformer design and imaging.
abstract: This is the second part of a two-paper series reporting a recent effort in the development of a high-frequency annular array ultrasound imaging system. In this paper an imaging system composed of a six-element, 43 MHz annular array transducer, a six-channel analog front-end, a field programmable gate array (FPGA)-based beamformer, and a digital signal processor (DSP) microprocessor-based scan converter will be described. A computer is used as the interface for image display. The beamformer that applies delays to the echoes for each channel is implemented with the strategy of combining the coarse and fine delays. The coarse delays that are integer multiples of the clock periods are achieved by using a first-in-first-out (FIFO) structure, and the fine delays are obtained with a fractional delay (FD) filter. Using this principle, dynamic receiving focusing is achieved. The image from a wire phantom obtained with the imaging system was compared to that from a prototype ultrasonic backscatter microscope with a 45 MHz single-element transducer. The improved lateral resolution and depth of field from the wire phantom image were observed. Images from an excised rabbit eye sample also were obtained, and fine anatomical structures were discerned.
authors.affiliation: Biomedical Engineering Department and NIH Transducer Resource Center, University of Southern California, Los Angeles, CA 90089, USA. changhoh@usc.edu
authors.forename: Chang-Hong
authors.initials: CH
authors.lastname: Hu
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Snook
authors.forename: Pei-Jie
authors.initials: PJ
authors.lastname: Cao
authors.forename: K Kirk
authors.initials: KK
authors.lastname: Shung
mesh_terms: D000818:Animals; D017076:Computer-Aided Design; D003315:Cornea / Q000000981:diagnostic imaging*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D066298:In Vitro Techniques; D011817:Rabbits; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D014159:Transducers; D014463:Ultrasonography / Q000295:instrumentation* / Q000379:methods