INTRAFILM CONTROLS TO STANDARDIZE GREY LEVEL VARIATIONS IN DIGITIZED RADIOGRAPHS

Objectives. Radiometric analysis can be used to identify small changes in grey levels taken from investigator-defined regions of interest (R OIs). To do this, standardization of the radiographic optical densitie s and image grey scales is considered essential. Rigid standardization is one of the impediments to applying existing radiometric techniques to clinical practice. The purpose of this study was to evaluate the u se of grey-level variations from a series of intrafilm control regions of interest (ROIs) to adjust radiometric grey-level data taken from t est ROIs. Methods. After digitization, ROIs were drawn on three locati ons: the background, anatomical crown, and tooth root. Mean grey level s, histograms and cumulative percent histograms (CPHs) were determined for each group. With the goal of decreasing the distribution of these curves from their unadjusted grey-level positions to zero (superimpos ing all curves), shifts required to align the control CPHs were applie d to test CPHs. Changes between the pre- and post-adjusted CPH distrib utions were measured. Results. Intrafilm controls provided a combined decrease of 45.3% in the grey-level distribution error. Conclusion. Wh ile CPHs can be adjusted using intrafilm controls, these adjustments m ay have limited benefit.