Fig 1.
Projection of a point (or any flat object).
The focus (F) of the X-ray beam is located at height (h) over the origin (O) of the xy-plane.
Fig 2.
A. Projection of a sphere. The focus (F) of the X-ray beam is located at height (h) over the origin (O) of the xy-plane. A sphere with radius (r) and the center (C) shifted from the X-ray beam by x0 (S) is projected to the xy-plane (|P’Q’|). B. Detailed view of the projection of a sphere with radius (r). The center of the sphere (C) and the projected length |PC| (w*) and |PQ| (w) are shown. A and B are cutting points of the tangential X-ray beam and the sphere.
Fig 3.
Standing AP radiograph of the pelvis with internal (asterix) and external calibration marker (arrow) and performed measurements: central beam (C); marker diameter; distances of the markers from the central beam; position of the markers.
Fig 4.
Graphs for radiographic magnification.
(A) Absolute size of the projection of a 28 mm sphere; (B) percentage of the overall magnification for a sphere of any diameter; (C) magnification of the horizontal shift alone. Each line represents a vertical position between 0 and 450 mm above the detector in 50 mm increments.
Table 1.
Baseline parameters of radiographic analysis.
Table 2.
Subgroups of external and internal calibration markers.
Table 3.
Magnification of internal and external calibration markers and difference of each case in percent.
Table 4.
Spearman correlation coefficients (r) for magnification of internal and external calibration markers and repeated measurements.
Fig 5.
Scatter-plot of the correlation of internal (ICM) and external calibration marker (ECM) of one measurement with the corresponding R2.
Linear regression line included.
Table 5.
Intraclass correlation coefficients for intra- and inter-observer reliability.