Sub-millimeter bistatic passive acoustic mapping

Passive acoustic mapping (PAM) is an emerging technique used to image sources of non-linear acoustic emissions, such as inertially cavitating bubbles, during ultrasound therapy. When using a conventional diagnostic ultrasound array, the transverse resolution is typically an order of magnitude better than the axial resolution, which may be inadequate for monitoring treatment at acoustically large distances from the array. Here, we describe an experimental technique that utilizes two orthogonal and coplanar 128-element linear arrays (6.25 MHz centre frequency) to overcome this limitation. The resolution of bistatic PAM was quantified by varying the distance between sources, as well as the array-to-sources distance. The optimal number of elements required was identified by considering the resolution, the accuracy in quantifying the energy of acoustic emissions, and the computational cost. The resulting resolution (achieved with 256 elements) was close to theoretical transverse resolution limit, on the order ...