The Hemisphere Model - A new description of directions for head radiographs in the horse

The Hemisphere Model is developed to specify directions of head radiographs very precisely even if different radiographic techniques are used. There is an imaginary globe around the head with two perpendicular sections. Two angles or geographic coordinates in these sections are sufficient to describe the direction of an x-ray beam. In this model the equator plane stays between the upper and lower jaw in the chewing surface. Thus, the upper jaw remains in the upper hemisphere and the lower jaw in the lower hemisphere. The 0 degrees mark is rostral on the equator and is the description for a straight rostrocaudal radiographic direction. The first geographic coordinate describes the deviation from straight rostral in the horizontal equator level between 0 degrees and 180 degrees. The laterolateral direction has a 90 degrees deviation from rostral and is given the coordinate 90 degrees (no matter if the direction is right to left or left to right). The second geographic coordinate describes the angle of the x-ray beam towards the horizontal equator level. If the x-ray beam comes from dorsal, the numbers are positive between +1 degrees and +90 degrees. If the x-ray beam comes from ventral, the numbers are negative between -1 degrees and -90 degrees. In radiographs of the cheek teeth or structures of the head, the side with contact to the cassette is labeled right or left.