Intrafilm controls to standardize grey level variations in digitized radiographs

Radiometric analysis can be used to identify small changes in grey levels taken from investigator-defined regions of interest (ROIs). To do this, standardization of the radiographic optical densities 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 use of grey-level variations from a series of intrafilm control regions of interest (ROIs) to adjust radiometric grey-level data taken from test ROIs.

After digitization, ROIs were drawn on three locations: the background, anatomical crown, and tooth root. Mean grey levels, 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 (superimposing all curves), shifts required to align the control CPHs were applied to test CPHs. Changes between the pre- and post-adjusted CPH distributions were measured.

Intrafilm controls provided a combined decrease of 45.3% in the grey-level distribution error.

While CPHs can be adjusted using intrafilm controls, these adjustments may have limited benefit.