Warped Optical-Flow Inter-Frame Reconstruction for Ultrasound Image Enhancement

Problem statement: Optical flow inter-frame enhancement is one of the techniques to improve the quality of ultrasound images by reducing the speckle noise. The performance depends on accuracy of the optical flow inter-frame reconstruction which is a part of the technique. The speckle noise of an ultrasound image forms certain pattern, of which size of the speckle varies depends on the distance from the transducer. Approach: This study proposed that the use of warping technique prior to as well as after the optical flow to improve the accuracy of the optical flow calculation. The warping function was derived to transform the image from circular grid to rectangular grid. Results: The technique was applied to a series of synthetic moving frames generated from actual ultrasound image taken from a patient heart. The technique improved the accuracy of motion vectors generated from the optical flow. The MSE of the reconstructed frame was also smaller using warped technique compared to that of the non-warped technique. Conclusion: The proposed warping operation was shown to be successful in increasing the accuracy of the frame reconstruction for the optical flow inter-frame enhancement technique.