Patent GB-1184582-A (GB)
Title: Improvements in Stereoscopic X-Ray Apparatus.
IPC: A61B6/02
Filed: 1967-05-24
Abstract: 1,184,582. Stereoscopic X-ray apparatus. GENERAL ELECTRIC CO. 24 May, 1967 [26 May, 1966], No. 24164/67. Headings H4F and H5R. [Also in Division G2] A stereoscopic X-ray apparatus comprises means, e.g. dual focus X-ray tube 12, for alternately projecting two X-ray beams through an object, e.g. patient 11, at an angle to one another, an image converter 17 located to receive the alternate mutually displaced images of the object and having output screen 18 for displaying visible images corresponding to the X-ray images, a polarizer 21 and analyser 27 located on a common single optical axis 19 from the screen so that in operation the visible images are transmitted through the polarizer and the analyser to the eyes of an observer 29, said polarizer having two polarizing areas with mutually orthogonal polarization vectors (shown in section in the figure) said two areas each occupying substantially half the field of view and being substantially symmetrically distributed on either side of a notional line 31 bisecting the polarizer and said analyser having a single polarizing area with a unidirectional vector, said polarizer and analyser being mounted for relative rotation with respect to each other about said optical axis in synchronism with the alternation of the beam projection whereby in operation the visible images are transmitted along two paths adjacent to and symmetrically disposed with respect to said optical axis for reception by the left eye and the right eye respectively of the observer through one or the other polarizing areas of the polarizer. Preferably an objective lens 20 is adjacent the screen 18 for directing the images through the polarizer 26 which is located so that some proportion of the light emanating from all parts of each image on the screen passes through both polarizing areas, a lens system 23, 26 magnifying and directing the images along to the exit pupil where the operator may view the images. The polarizer may be stationary and the analyser mounted for rotation, e.g. using races 38, 39, gear teeth 40, pinion 41 and motor 42. The optical path may include at least one mirror, e.g. 22, 24, 25, to direct the image to viewing mirror 28, and the apparatus may be arranged (Fig. 5, not shown) so that a plane perpendicularly bisecting the line joining targets 14 is parallel to the plane perpendicularly bisecting the line joining the eyes of the observer both planes being inclined at a desired angle to the longitudinal symmetry plane of the patient support 10 and patient 11, the mirror 28 being rotated through the same angle about a vertical axis passing through the centre thereof. The notional line 31 of the polarizer may also be arranged to be parallel to said planes, the polarization vectors extending parallel and perpendicular to the longitudinal axis of the patient support. A reciprocating motion may be imparted to the X-ray source or sources to improve depth perception. A reversing switch may be incorporated so that a 180-degree phase shift can be introduced into the synchronism between the rotation of the analyser and the alternation of the beam so that the viewing system can be moved from one side of the patient to the other without reversing the image or a given aspect of the image may be viewed with the opposite eye. The X-ray source may comprise two cathodes with individual control grids, with a circuit arrangement to apply a bias voltage between the grids and the cathodes, a pulse generator and a commutator switch being fitted to produce and direct alternate pulses to the alternate control grids to permit alternate and sequential generation of the two beams, said commutator switch and the analyser being driven synchronously by a common drive means. In a preferred embodiment, the reversing switch mentioned above merely reverses the grids to which the alternate pulses from the generator are applied.