Fluid Registration of Ultrasound using Multi-scale Phase Estimates

We consider the registration of successive images over a cardiac ultrasound sequence. A key challenge is speckle. We suggest that, for practical purposes, speckle should be regarded as the sum of two components: the useful, temporally correlated speckle pattern; and speckle noise, which is the unpredictable change in the speckle pattern. We also propose that an increase in robustness can be obtained by modelling the spatial correlation of speckle noise. A model is introduced that captures the correlation of speckle noise, by separating the noise into sub-bands and measuring variance within each sub-band and covariance between bands. In order to gain contrast invariance, we express similarity between sub-bands in terms of local phase only, and describe a phase-based extension of the Demons algorithm. The parameters estimated from the noise model significantly enhance the already good registration performance of the phase-demons algorithm.