  We present an adaptation of the pixel-reassignment technique from confocal
fluorescent microscopy to coherent ultrasound imaging. The method, Ultrasound
Pixel-Reassignment (UPR), provides a resolution and signal to noise (SNR)
improvement in ultrasound imaging by computationally reassigning off-focus
signals acquired using traditional plane-wave compounding ultrasonography. We
theoretically analyze the analogy between the optical and ultrasound
implementations of pixel reassignment, and experimentally evaluate the imaging
quality on tissue-mimicking acoustic phantoms. We demonstrate that UPR provides
a $25\%$ resolution improvement and a $3dB$ SNR improvement in in-vitro scans,
without any change in hardware or acquisition scheme.
