 While classical registration methods can accurately align multi-modal image pairs , they solve a costly optimization problem for every new pairof images . Learning-based techniques are fast at test time, but can only register images of the specific anatomy and modalities they were trained on .
<clarity>  While classical registration methods can accurately align multi-modal image pairs , they solve a costly optimization problem for every new pairof images . Learning-based techniques are fast at test time, but can only register images of the specific anatomy and modalities they were trained on .
 While classical registration methods accurately estimate the spatial correspondence between images , they solve a costly optimization problem for every new pairof images . Learning-based techniques are fast at test time, but can only register images of the specific anatomy and modalities they were trained on .