LIGHT SOURCE-INDUCED ERROR ILL COMPUTER-ASSISTED IMAGE-ANALYSIS WITH A VIDEO-BASED SYSTEM

Objective. We tested the hypothesis that two different light sources, an alternating current fluorescent viewbox and a direct current haloge n viewbox, do not differ with respect to their ability to illuminate r eproducibly a radiograph during image capture. Study design. Two radio graphs were taken: one with four hydroxyapatite chips mounted against a dry mandible and one without the chips. They were digitally subtract ed with a video-based imaging system. The procedure was repeated at di fferent times. Results. A statistically significant difference among o ptical density measurements was found when the alternating current flu orescent viewbox (p < 0.001) was used and was related to light intensi ty variation. Such effect was not observed with the direct current hal ogen viewbox (p = 0.873). Conclusion. Study design efficiency was incr eased by 212% with the use of the direct current halogen viewbox so th at to detect a specified treatment effect with a given level of statis tical confidence, the sample size has to be 2.12 times greater if the alternating current fluorescent viewbox is used.