Two stage sub-wavelength motion correction in human microvasculature for CEUS imaging

The structure of microvasculature cannot be resolved using clinical B-mode or contrast-enhanced ultrasound (CEUS) imaging due to the fundamental diffraction limit at clinical ultrasound frequencies. It is possible to overcome this resolution limitation by localizing individual microbubbles through multiple frames and forming a super-resolved image. However, ultrasound super-resolution creates its unique problems since the structures to be imaged are on the order of 10s of μm. Tissue movement much larger than 10 μm is common in clinical imaging, which can significantly reduce the accuracy of super-resolution images created from microbubble locations gathered through hundreds of frames. This study investigated an existing motion estimation algorithm from magnetic resonance imaging for ultrasound super-resolution imaging. Its correction accuracy is evaluated using simulations with increasing complexity of motion. Feasibility of the method for ultrasound super-resolution in vivo is demonstrated on clinical ultrasound images. For a chosen microvessel, the super-resolution image without motion correction achieved a sub-wavelength resolution; however after the application of proposed two-stage motion correction method the size of the vessel was reduced to half.