Stereo-cinefluorography; motion roentgenography in three dimensions.

Abstract

The basic principles of cardiac function and control have been derived from experiments on the hearts of anesthetized thoracotomized animals. Recently, however, evidence has been presented that the heart shrinks significantly during thoracotomy and that observations on the exposed organ may not apply to intact animals and man (1). Roentgenographic technics are extremely valuable for both basic and clinical investigation, since they permit visualization of the undisturbed heart within the thorax. Recording the images on fluorescent screens (cinefluorography) has proved useful for studying cardiovascular function (2). Cinefluorographic angiocardiography has revealed the movement of blood through veins, cardiac chambers, and arteries. Analysis of the photographed movement of the metal markers mounted on the heart walls has provided additional information concerning details of cardiac contraction (3). Since fluoroscopic images represent the projection of three-dimensional structures onto a two-dimensional plane, roentgenographic observation has been limited largely to analyzing the movements of the borders of the shadows cast by vascular structures. To broaden the application of roentgenographic studies of internal organs, a technic for three-dimensional visualization of cinefluorographic films has been developed. The Basis of Three-Dimensional Visualization The position of an object in space is recognized by a number of visual clues: (i) Distant objects cast a smaller image on the retina. (ii) Lights, shadows, and perspective give clues as to the form and position of objects. (iii) Objects nearer than 20 feet require varying degrees of accommodation of the lens to focus the image on the retina. (iv) The eyes must converge a specific amount to obtain a fused image of an object which is near at hand. (Accommodation and convergence are normally regulated by nervous reflexes so that focus on the retina and fusion of an image are automatically attained.) (v) When the eyes are focused on a single point in space, objects nearer or farther away are somewhat out of focus and appear as double images (physiological diplopia). (vi) If two objects are traveling at the same rate, the one which is closer to the observer appears to move faster. During rotation around an axis, points on the near side move in one direction and those on the far side move in the other. (For example, the horses on a merry-go-round move to the right on the near side and to the left on the far side.) (vii) The eyes are separated by a slight distance so that slightly different images fall on the two retinas (binocular parallax). (The nearer an object is to the eyes, the greater will be the difference between the two retinal images.) Shadows or silhouettes cast on a single plane lose their three-dimensional reference because the eyes are focused on a flat screen or x-ray plate.