A method, comprising: determining a registration transform between first three dimensional pre-scan image data and second three dimensional pre-scan image data based on a predetermined registration algorithm; and registering first volumetric scan image data and second volumetric scan image data based on the registration transform, generating registered image data, characterised in that the first three dimensional pre-scan image data and the second three dimensional pre-scan image data are acquired at a first motion state and the first volumetric scan image data and the second volumetric scan image data are acquired at a second, different motion state, and further comprising: determining a first motion vector field for the first volumetric scan image data based on the first volumetric scan image data and the first three dimensional pre-scan image data; determining a second motion vector field for the second volumetric scan image data based on the second volumetric scan image data and second three dimensional pre-scan image data; motion compensating the first volumetric scan image data based on the first motion vector; motion compensating the second volumetric scan image data based on the second motion vector; and registering the motion compensated first volumetric scan image data and the motion compensated second volumetric scan image data based on the registration transform, generating the registered image data. determining a registration transform between first three dimensional pre-scan image data and second three dimensional pre-scan image data based on a predetermined registration algorithm; and registering first volumetric scan image data and second volumetric scan image data based on the registration transform, generating registered image data, characterised in that the first three dimensional pre-scan image data and the second three dimensional pre-scan image data are acquired at a first motion state and the first volumetric scan image data and the second volumetric scan image data are acquired at a second, different motion state, and further comprising: determining a first motion vector field for the first volumetric scan image data based on the first volumetric scan image data and the first three dimensional pre-scan image data; determining a second motion vector field for the second volumetric scan image data based on the second volumetric scan image data and second three dimensional pre-scan image data; motion compensating the first volumetric scan image data based on the first motion vector; motion compensating the second volumetric scan image data based on the second motion vector; and registering the motion compensated first volumetric scan image data and the motion compensated second volumetric scan image data based on the registration transform, generating the registered image data. determining a first motion vector field for the first volumetric scan image data based on the first volumetric scan image data and the first three dimensional pre-scan image data; determining a second motion vector field for the second volumetric scan image data based on the second volumetric scan image data and second three dimensional pre-scan image data; motion compensating the first volumetric scan image data based on the first motion vector; motion compensating the second volumetric scan image data based on the second motion vector; and registering the motion compensated first volumetric scan image data and the motion compensated second volumetric scan image data based on the registration transform, generating the registered image data.