Efficient sub-diffraction passive cavitation imaging

Abstract

Acoustic localization of microbubbles offers a unique method to assess vascular structure and function noninvasively. To this end, passive imaging of the acoustic cavitation with the angular spectrum method (AS-PCI) is appealing as it is inherently fast and frequency-selective and thus allows stable cavitation activity to be isolated from other scatters via the bubbles’ harmonic emissions. However, diffraction imposes a physical limitation on the resolution of acoustic imaging systems, which is typically on the order of millimeters for PCI. To enable rapid visualization of vessel structures with diameters of few hundreds of microns, we present a technique based on the AS method for fast super-localization (SL) of multiple, spatially separated bubbles that is 100-fold more efficient than time domain techniques employed for resolution improvement. We demonstrate, via experiments and numerical simulations, that it is possible to super-localize multiple bubbles within a single image and resolve vessels with diameters 10 times smaller than the diffraction limit (300 µm vs. 3 mm, respectively). Furthermore, successive super-localization of hundreds of microbubbles with the proposed SL-AS-PCI method allowed visualization of three-dimensional vessel structures within a few seconds on ordinary hardware. SL-AS-PCI holds great promise for efficient diagnosis of diseases associated with abnormal vasculature.