Distortion map and correction for ultrasound localization microscopy imaging with a row–column array

Abstract

The row–column array is an emerging technology which can enable large fields of view without the need for a large number of electronic channels. In ultrasound localization microscopy, sparse microbubbles are localized and tracked to produce high-resolution images of the microvasculature. During the localization of the microbubbles, it is typically assumed that the center of the target observed can be used as a substitute for the true microbubble location. However, the true microbubble will be located at the onset of the received signal. This distortion between the true location and the observed location will result in a shift of the microbubble away from the true location, thus altering the accuracy of the images produced. In most forms of ultrasound imaging, this shift mostly manifests as a vertical shift so can often be safely ignored. However, we have observed that in row–column array imaging this distortion will be spatially variable and will result in distortions in the axial, elevational, and lateral directions, which can be on the order of a few wavelengths. Consequently, this distortion, if ignored, will result in inaccuracies in the resulting ultrasound localization microscopy images. Here, we present a technique to map and correct for these distortions.