TABLE II.

Selected unsupervised transformation prediction methods

References	ROI	Patch- based	Modality	Transform	Similarity
[9]	Brain	No	MR	Deformable	SSD
[10]	Brain	No	MR	Affine	MI
[11, 12]	Brain	Yes	MR	Deformable	Intensity & gradient difference
[22]	HN	Yes	CT	Deformable	MSE
[28]	Cardiac	No	MR	Deformable	CC
[34]	Lung	No	MR	Deformable	MSE
[36]	Brain	No	MR-US	Deformable	MSE after intensity mapping
[37]	Cardiac, Lung	Yes	MR, CT	Affine and Deformable	MSE
[38, 39]	Brain	No	MR	Deformable	CC
[40]	Liver	No	CT	Deformable	CC
[41, 42]	Brain	No	MR	Deformable	CC
[44]	Liver	No	CT	Deformable	CC
[46]	Abdomen	Yes	CT	Deformable	CC
[47]	Abdomen	Yes	CT	Deformable	CC
[49]	Lung	Yes	CT	Deformable	CC
[51, 52]	Prostate	No	MR-TRUS/CBCT	Deformable	None
[54]	Lung, Cardiac	Yes	CT, MRI	Deformable	CC