A method of registering first image data of a first stream with second image data of a second stream, the first image data and the second image data comprising image information about a person or animal including image information about at least one organ (Or) of the person or animal, wherein a shape and/or position of the organ (Or) is changing thereby performing a cyclic change of the shape and/or position, and wherein: • each of the first stream and the second stream comprises a series of images of the at least one organ (Or) at a plurality of different discrete stages of the cyclic change of the shape and/or position so that each of the images corresponds to one of the discrete stages of the cyclic change of the shape and/or position, • a phase variable (p) is used to define the stage of the cyclic change of the shape and/or position and a phase value of the phase variable (p) is assigned to each of the images within each of the first and second stream thereby defining unambiguously the discrete stage of the cyclic change of the shape and/or position represented by the image instead of the time during a specific cycle when the image was taken, • a registration, i.e. location-to-location associations of image values, is determined for a pair of images consisting of a first image of the first stream and a second image of the second stream, wherein the first image and the second image of the pair are selected by choosing or interpolating an image from the first stream and by choosing or interpolating an image from the second stream to which the same phase value (pr) is assigned, characterized in that • at least two registrations, i.e. location-to-location associations of image values, are determined, namely one registration for each of different pairs consisting in each case of a first image of the first stream and a second image of the second stream, wherein the first image and the second image of each of the different pairs are selected by choosing or interpolating an image from the first stream and by choosing or interpolating an image from the second stream to which the same phase value is assigned, thereby achieving for each of the different pairs a description of the location-to-location associations between the first image and the second image, • an interpolated description of location-to-location associations between a first image and a second image of a new pair of images is determined using the phase variable (p) as an independent variable of interpolation, wherein one existing image of the first image and the second image of the new pair exists as acquired image or as a result of an interpolation and the other image of the first image and the second image of the new pair is to be generated, a desired phase value of the phase variable (p) being assigned to the existing image, • the other image is generated by applying the interpolated description of location-to-location associations to the existing image. • each of the first stream and the second stream comprises a series of images of the at least one organ (Or) at a plurality of different discrete stages of the cyclic change of the shape and/or position so that each of the images corresponds to one of the discrete stages of the cyclic change of the shape and/or position, • a phase variable (p) is used to define the stage of the cyclic change of the shape and/or position and a phase value of the phase variable (p) is assigned to each of the images within each of the first and second stream thereby defining unambiguously the discrete stage of the cyclic change of the shape and/or position represented by the image instead of the time during a specific cycle when the image was taken, • a registration, i.e. location-to-location associations of image values, is determined for a pair of images consisting of a first image of the first stream and a second image of the second stream, wherein the first image and the second image of the pair are selected by choosing or interpolating an image from the first stream and by choosing or interpolating an image from the second stream to which the same phase value (pr) is assigned, • at least two registrations, i.e. location-to-location associations of image values, are determined, namely one registration for each of different pairs consisting in each case of a first image of the first stream and a second image of the second stream, wherein the first image and the second image of each of the different pairs are selected by choosing or interpolating an image from the first stream and by choosing or interpolating an image from the second stream to which the same phase value is assigned, thereby achieving for each of the different pairs a description of the location-to-location associations between the first image and the second image, • an interpolated description of location-to-location associations between a first image and a second image of a new pair of images is determined using the phase variable (p) as an independent variable of interpolation, wherein one existing image of the first image and the second image of the new pair exists as acquired image or as a result of an interpolation and the other image of the first image and the second image of the new pair is to be generated, a desired phase value of the phase variable (p) being assigned to the existing image, • the other image is generated by applying the interpolated description of location-to-location associations to the existing image.