A method for compensating motion in positron emission tomographic, PET, data comprising coincident lines of response from positron-emitting position markers, the method comprising: - detecting a slippage of one or more of the position markers; - deriving a plurality of images from the PET data, and, identifying therefrom, based on the detected slippage, a first set of images before the detected slippage and a second set of images after the detected slippage; - motion correcting the first and second set of images, thereby obtaining a first and a second motion-compensated set of images; - determining slippage correction parameters based on the first and second motion-compensated set of images; and - applying motion correction to the PET data by taking into account the slippage correction parameters, thereby obtaining a motion-compensated PET data; and wherein the motion correcting further comprises: - deriving motion correction parameters for the first and second set of images; - applying the derived motion compensation parameters to the respective set of images, thereby obtaining the first and second motion-compensated set of images from the respective first and second set of images; and wherein the determining slippage correction parameters further comprises: - masking the position markers in the first and second motion-compensated set of images and registering the first and second motion-compensated and masked set of images; and wherein the applying motion correction further comprises: - correcting the motion correction parameters with the slippage correction parameters. - detecting a slippage of one or more of the position markers; - deriving a plurality of images from the PET data, and, identifying therefrom, based on the detected slippage, a first set of images before the detected slippage and a second set of images after the detected slippage; - motion correcting the first and second set of images, thereby obtaining a first and a second motion-compensated set of images; - determining slippage correction parameters based on the first and second motion-compensated set of images; and - applying motion correction to the PET data by taking into account the slippage correction parameters, thereby obtaining a motion-compensated PET data; and wherein the motion correcting further comprises: - deriving motion correction parameters for the first and second set of images; - applying the derived motion compensation parameters to the respective set of images, thereby obtaining the first and second motion-compensated set of images from the respective first and second set of images; - deriving motion correction parameters for the first and second set of images; - applying the derived motion compensation parameters to the respective set of images, thereby obtaining the first and second motion-compensated set of images from the respective first and second set of images; and wherein the determining slippage correction parameters further comprises: - masking the position markers in the first and second motion-compensated set of images and registering the first and second motion-compensated and masked set of images; - masking the position markers in the first and second motion-compensated set of images and registering the first and second motion-compensated and masked set of images; and wherein the applying motion correction further comprises: - correcting the motion correction parameters with the slippage correction parameters. - correcting the motion correction parameters with the slippage correction parameters.