An apparatus for diagnostic imaging comprising: - a first memory means for storing a first diagnostic image; - a second memory means for storing a second diagnostic image; - a registering means for automatically registering the first and second diagnostic images from the first and second image memories without operator assistance, the registering means further including: an affine transformation determining means for determining an affine transformation representative of misalignment of the first and second diagnostic images; - a means for operating on one of the first and second diagnostic images in accordance with the determined affine transform to register the first and second diagnostic images; - a means (104, 22) for concurrently displaying a corresponding pair of slices of the registered first and second diagnostic images - a means for replacing the displayed corresponding pair of slices of the first and second diagnostic images with another corresponding pair of slices of the first and second diagnostic images, characterized in that: said first diagnostic image is a first diagnostic image of the lungs of a patient, said second diagnostic image is a second diagnostic image of the lungs of said patient, and said affine transformation determining means further includes a number of points reducing means arranged for selectively and non-uniformly reducing a number of points to be used in determining said affine transformation, wherein points which influence the registration along a longitudinal axis are favored in said reducing of points, wherein a higher percentage of points are selected along the top and bottom of the lungs. - a first memory means for storing a first diagnostic image; - a second memory means for storing a second diagnostic image; - a registering means for automatically registering the first and second diagnostic images from the first and second image memories without operator assistance, the registering means further including: an affine transformation determining means for determining an affine transformation representative of misalignment of the first and second diagnostic images; an affine transformation determining means for determining an affine transformation representative of misalignment of the first and second diagnostic images; - a means for operating on one of the first and second diagnostic images in accordance with the determined affine transform to register the first and second diagnostic images; - a means (104, 22) for concurrently displaying a corresponding pair of slices of the registered first and second diagnostic images - a means for replacing the displayed corresponding pair of slices of the first and second diagnostic images with another corresponding pair of slices of the first and second diagnostic images, said first diagnostic image is a first diagnostic image of the lungs of a patient, said second diagnostic image is a second diagnostic image of the lungs of said patient, and said affine transformation determining means further includes a number of points reducing means arranged for selectively and non-uniformly reducing a number of points to be used in determining said affine transformation, wherein points which influence the registration along a longitudinal axis are favored in said reducing of points, wherein a higher percentage of points are selected along the top and bottom of the lungs.