A COMPUTER-ASSISTED METHOD FOR MAKING LINEAR RADIOGRAPHIC MEASUREMENTS USING STORED REGIONS OF INTEREST

Accurate detection of changes in alveolar bone height requires radiographic measuring methods with a reliability of standard deviation (SD) of 0.15 mm or better. No periodontal digital imaging system has reached this reliability. although 3 analogue methods have achieved this goal. However, existing linear methods are time-consuming, difficult to use, unsuitable for measuring all possible (unsharp) anatomical sites and do not provide a confidence estimate for sites of change observed in serial standardized films. A rapid computer-assisted method using stored image regions of interest (ROI) has been developed which allows retest measurements for all possible sites and automatically calculates a 90%, 95%, 98% or 99% confidence threshold value, derived from duplicate measurement variation, for sites of apparent crest height change. 28 examiners, with minimal training in operating the system, measured 14 different cement-enamel junction to crest height distances from a standard bitewing image, with and without the ROI method. The measurements were repeated 4 weeks later. 13/14 sites achieved an intra-examiner SD threshold of less-than-or-equal-to 0.15 mm with the ROI method but 0/14 without. A higher inter-examiner SD threshold of less-than-or-equal-to 0.22 mm was achieved for 13/14 sites using ROI and 0/14 without (p < 0.001). The measurement of crest height changes in a region of previous severe vertical bone loss is demonstrated using serial films. The potential for using trabecular bone patterns as reference sites in regions where traditional measurement points are absent is demonstrated. A possible method for investigating the validity of comparing serial films, with regard to irradiation geometry changes, is shown using measurements of approximal surface overlap.