A method for at least reducing the occurrence of differential ghosting in an X-ray image acquired in respect of a subject, wherein a deghost scan is performed at least once daily so as to generate an underlying strong homogeneous ghost so that further differential (non-homogeneous) ghosting during subsequent scans is minimised. The deghost scan comprises acquiring an ‘air’ image, when no subject is present between the X-ray source (4) and detector (5), as a relatively high detector dose.