Implementation of Tissue Harmonic Synthetic Aperture Imaging on a Commercial Ultrasound System

This paper presents an imaging technique for synthetic aperture (SAI) tissue harmonic imaging (THI) on a commercial ultrasound system. Synthetic aperture sequential beamforming (SASB) is combined with a pulse inversion (PI) technique on a commercial BK 2202 UltraView system. An interleaved scan sequence that performs dynamic receive focused (DRF) imaging and SASB, both using PI, is implemented.

From each acquisition four images can be created: DRF image, SASB image, tissue harmonic DRF image (DRF-THI), and tissue harmonic SASB image (SASB-THI). For SASB imaging, a fixed transmit and receive focus at 80 mm and an F# of 3 is applied. For DRF imaging, default scanner settings are used, which are a focus at 85 mm and F# of 5.7 in transmit and a dynamic receive aperture with an F# of 0.8.

In all cases a 2.14 MHz one-and-ahalf cycle excitation transmit waveform is used. A BK 8820e 192 element convex array transducer is used to conduct scans of wire phantoms. The -6 dB and -20 dB lateral resolution is measured for each wire in the phantom. Results show that the -6 dB lateral resolution for SASB-THI is as good as for DRF-THI except at the point of the virtual source.

SASB-THI even shows 7% reduction in -6 dB lateral resolution for the deepest wire at 100 mm. The -20 dB resolution for SASB-THI at [25, 50, 75, 100] mm was reduced by [5, 0 -34, 11] % compared to DRF-THI, which shows, that except for the point of the virtual source, the lateral resolution was improved by SASB-THI.

A successful implementation of SASB-THI was achieved on a commercial system, which can be used for future pre-clinical trials.