Vibro-acoustography beamforming and imaging with a 1.75D array transducer

Vibro-acoustography (VA) is an ultrasound-based imaging modality that uses radiation force produced by two confocal ultrasound beams separated by small frequency difference, Δf, to vibrate tissue at Δf. We used a 1.75D transducer with 12 rows and 70 columns of elements with size 0.9 x 0.9 mm. The point-spread functions (PSFs) for different configurations of the subapertures for the two frequencies centered about 5 MHz were evaluated using a numerical simulation model using Field II. Experimentally, we scanned the pressure field for different configurations using a needle hydrophone to evaluate the PSF. Finally, we scanned a urethane breast phantom and an ex vivo human prostate. We evaluated the PSFs from the simulations and needle hydrophone scans and found good agreement. We quantitatively analyzed the grating lobe levels of the PSFs for the different configurations. We compared images generated using different configurations of the subapertures in the urethane breast phantom and ex vivo human prostate. The advantage of the 1.75D array transducer is the multiple rows of elements that can be used for improving elevation focus for imaging formation. VA imaging using a 1.75D array transducer provides improved image detail and contrast due to better elevation focusing of the imaging PSF.