Position-Dependent Defocus Processing for Acoustic Holography Images

摘要

Acoustic holography is a transmission-based ultrasound imaging method that uses optical image reconstruction and provides a larger field of view than pulse-echo ultrasound imaging. A focus parameter controls the position of the focal plane along the optical axis, and the images obtained contain defocused content from objects not near the focal plane. Moreover, it is not always possible to bring all objects of interest into simultaneous focus. In this article, digital image processing techniques are presented to (1) identify a "best focused" image from a sequence of images taken with different focus settings and (2) simultaneously focus every pixel in the image through fusion of pixels from different frames in the sequence. Experiments show that the three-dimensional image information provided by acoustic holography requires position-dependent filtering for the enhancement step. It is found that filtering in the spatial domain is more computationally efficient than in the frequency domain. In addition, spatial domain processing gives the best performance.