Synthetic Aperture High Quality B-mode Imaging with a Row-Column Array Compared to Linear Array Imaging

Row-column (RC) matrix probes can yield 3-Dvolumetric imaging using a number of receiving elements similarto traditional linear arrays for commercial scanners. Some doubtshave, however, been raised on the B-mode image quality ofRC probes. It is hypothesized that synthetic aperture (SA) RCimaging can yield a better volumetric resolution than commercialspatially translated linear arrays, and at the same time attainvolume rates similar to frame rates for single slice linear arrayscanning. A Vermon 6 MHz 128×128 elements RC array withλ pitch was used on a Verasonics Vantage 256 scanner. A SAsequence with 2 × 96 emissions on the rows and columns andreception on all 128 orthogonal elements were employed giving a62.5 Hz volume rate for a pulse repetition frequency of 12 kHz.The resolution and contrast were compared to an optimized SAsequence for a 256-elements GE L3-12D 6 MHz linear arrayprobe, where the volume was acquired using a linear probetranslation in the elevation direction. Imaging was conductedon a 3-D printed point spread function (PSF) phantom withscattering voids in a 6×4×4 grid with a 2.05 mm spacing in allthree directions. The exposed kidney of a Sprague-Dawley ratwas also scanned in vivo with the RC probe. B-mode imagesof the 3-D printed PSF phantom were shown with a 40 dBdynamic range along with the linear array scans. An isotropicresolution of (1.05λ,1.10λ,0.62λ) = (x, y,z) was obtained for therow-column probe. The linear array probe had an elevationresolution determined by the geometric elevation focus of thearray, and therefore the four rows of point scatterers could not bedifferentiated in the elevation direction due to the fixed elevationfocus. The data rates were identical for the two arrays, but the RCarray yielded an isotropic PSF with an improved contrast, and a62.5 Hz volume rate comparable to normal linear array imaging.In vivo kidney images for the three orthogonal planes were shownwith a 60 dB dynamic range demonstrating the isotropic specklepattern in all three directions for all depths. The SA imagingRC sequence thus yielded a PSF independent of orientation anddepth. Any slice plane in the volume therefore had a uniformspeckle pattern, contrast, and resolution, demonstrating thatRC arrays can yield higher quality B-mode images than lineararrays. The penetration depth of the probe and sequence wasalso measured to be 550λ corresponding to 141 mm.