Measurement of fine structures in roentgenograms I. A microdensitometric method

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Abstract
A microdensitometer incorporating a rebuilt light microscope is described. In this apparatus, light from a stabilized source passes through a film and impinges on a photomultiplier attached to the microscope. The voltage generated by the light is read on a digital multimeter. The coefficient of variation of the densitometric measurements in the range of measurement of interest for analysis of dental roentgenograms was less than 3 %. The conversion of pairs of voltage measurements to aluminium equivalents, which reflect differences in substance in the object, and to «optical density units» (ODU), which express differences in image contrast, is described. Roentgenograms of simulated tooth roots, parallel ivory cones with central canals, were analyzed in the densitometer. The breadth of the image of the canal in the plane of the film was measured as was the photographic density of the image of the canal which was used to estimate the depth of the canal and the contrast between its image and that of the' surrounding dentine. The precision of the methods of measurement of the breadth was 0.13 mm, and of the differences in substance and contrast, 0.05 mm A1 and 0.03 ODU, respectively.

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