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Roentgen stereophotogrammetry. A method for the study of the kinematics of the skeletal system.

Author information

1
University of Lund, Department of Anatomy, Sweden.

Abstract

I have developed a roentgen stereophotogrammetric method for determination of positions of radiopaque markers in an object. The space coordinates are determined in a laboratory coordinate system, which is defined by markers in a test "cage". The markers in the test cage function as calibration points, and are roentgenographed on the same film(s) as the object. Calibration markers and object markers are exposed from two roentgen foci. The cage markers, are in their function, of two kinds, of which one (fiducial marks) is used for projective transformations of the image points to the laboratory coordinate system, while the other (control points) is used for determining the roentgen foci positions in the same coordinate system. After these calculations have been performed, the three-dimensional coordinates of object indicators are determined by crossing of lines between the roentgen foci and the transformed image points. The mathematical principles for the reconstruction of the bundles of rays from the roentgen foci at the moment of exposure are discussed in Chapter 2. Three constructions of test cages, Models 1A and 1B, and Model 2 are also discussed there. In Test Cage Model 1, the two exposures of the object are obtained on one film, but in Model 2 we expose on two films that are perpendicular to each other. The three cage models are, in turn, intended for high-accuracy determinations of lengths (Model 1A), general determinations of space coordinates, especially in larger objects (Model 1B), and high-accuracy determinations of space coordinates in medium-sized objects (Model 1B), and high-accuracy determinations of space coordinates in medium-sized objects (Model 1B). Note, that if the positions of the roentgen foci and the film are not altered, we can roentgenograph the calibration points separately on a film, and then, after removal of the test cage, roentgenograph the object on the same film. The calibration of the test cages is discussed in Chapter 3. To determine coordinates of markers in a plane is easy, if a rectangular coordinatograph is accessible, and we use the same instrument as for the measurements of the films, a Wild Autograph A8. Determination of the position in space of the plate with control points in relation to the plate with fiducial marks requires more consideration. We describe how the degrees of freedom of the plate with control points (translations in x- and y-directions, rotation angle phi about a z-axis), which are difficult to control at construction of the test cages, can be determined by specific calibration procedures.(ABSTRACT TRUNCATED AT 400 WORDS).

PMID:
2686344
[Indexed for MEDLINE]

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