Methods for positioning an internal portion of a body relative to an extracorporeal referent

A method of positioning a small internal portion of a body at a predetermined point relative to an extracorporeal referent, said body portion being detectable by penetrating radiation and said body being initially so disposed that the body portion is generally adjacent said predetermined point, said method comprising

• (a) viewing said body with penetrating radiation along two convergent viewing axes intersecting at said predetermined point for producing two images of the interior of the body as viewed by said penetrating radiation respectively along said two viewing axes, each of said images including a portion representing said body portion;
• (b) determining, from said two images, two-dimensional coordinates of the projections of the imaged body portion by the pentrating radiation on two notional planes respectively perpendicular to the viewing axes of the images, thereby to establish two sets of two-dimensional body portion coordinates, one for each image;
• (c) from said two sets of two-dimensional coordinates, deriving for each image spatial coordinates of the imaged body portion in a coordinate system having as one axis the viewing axis of the image, thereby to establish two sets of three-dimensional body portion coordinates, one for each image;
• (d) transforming said two sets of three-dimensional coordinates into a single set of three-dimensional coordinates in a common coordinate system in which the coordinates of said predetermined point are known, said single set of three-dimensional coordinates representing the location of said body portion in said last-mentioned system, thereby to determine the magnitude and direction of movement of said body required to position said body portion at said predetermined point;
• and
• (e) displacing said body with a resultant motion having said magnitude and direction.