1. A method of establishing a position of one or more constituent elements of a phantom in an image quality test for a medical imaging apparatus, comprising the steps of: operating the medical imaging apparatus to obtain an image of the phantom; providing said image to a processor and, in said processor, determining a landmark pixel or region of the image; in said processor, obtaining values of a given variable at each of a plurality of pixels or regions at a predetermined radius from the landmark pixel or region; after obtaining the values of the variable at the radius, obtaining, in said processor, a sequence of the values around a circumference defined by the radius; in said processor, comparing the sequence to an expected sequence for the values around the circumference; and in said processor, using the landmark pixel or region and the values of the given variable to establish the position of one or more constituent elements of the phantom, and making said position available as an electronic signal at an output of said processor.