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Abstract: Non-rigid image registration techniques are commonly used to estimate complex tissue deformations in medical imaging. A range of non-rigid registration algorithms have been proposed, but they typically have high computational complexity. To reduce this complexity, combinations of multiple less complex deformations have been proposed such as hierarchical techniques which successively split the non-rigid registration problem into multiple locally rigid or affine components. However, to date the splitting has been regular and the underlying image content has not been considered in the splitting process. This can lead to errors and artefacts in the resulting motion fields. In this paper, we propose three novel adaptive splitting techniques, an image-based, a similarity-based, and a motion-based technique within a hierarchical framework which attempt to process regions of similar motion and/or image structure in single registration components. We evaluate our technique on free-breathing whole-chest 3D MRI data from 10 volunteers and two publicly available CT datasets. We demonstrate a reduction in registration error of up to 49.1% over a non-adaptive technique and compare our results with a commonly used free-form registration algorithm. [Copyright &y& Elsevier]

Highlights: [•] A new 3D velocity recovery method from 3+registered Doppler images is presented. [•] Variations in Doppler images are simulated with a new multiscale noise model. [•] We carry out a sensitivity analysis to view angles, noise and registration errors. [•] Error in volume on 3 volunteers agree with predicted error from simulation studies. [•] Preliminary results on three patients are accurate and capture complex flow patterns. [Copyright &y& Elsevier]