Abstract: A device determines the location of a point, line, or plane in space with respect to an object along an axis of projection from the object. The device includes a beam generator coupled to the object and generating a plane of light containing the axis of projection of the object. Additionally, the beam generator generates a ray of light oriented at an angle to the axis of the projection so as to intercept the axis at the point in space to be located. The position of the axis of projection in the plane is marked, preferably, by a second beam generator generating a plane of light containing the axis of projection of the object and oriented at an angle to the first plane. The coincidence of the ray and marking of the axis of projection in the plane indicates that the point in space has been located with respect to the object. The second beam generator may also provide a ray of light intersecting the axis of projection at a point different than the first ray.

Abstract: An indicator for indicating a dimension of an X-ray beam defined by a collimator has a base member positioned on the other side of the patient from the X-ray beam source. A pair of light sources are mounted on the base member for linear movement and for angular movement so that the beams of light may be positioned into congruency with the edges of the X-ray field defined by the collimator and converge at the source of the X-ray beam. The light sources may be moved by a cable having selectively movable segments to which the light sources are attached or by lead screws.