ANALYTICAL METHODOLOGY IN QUANTITATIVE DIGITAL SUBTRACTION RADIOGRAPHY - ANALYSES OF THE ALUMINUM REFERENCE WEDGE

AN ALUMINUM WEDGE CAN BE USED TO QUANTIFY volumetric change in crestal alveolar bone which has been identified through subtraction radiograp hy. This study compares two methods for using an aluminum wedge for th is purpose: 1) the aluminum wedge is present in both radiographs and u sed to determine the aluminum equivalent bone density present in the r egion of change for each radiograph; and 2) the aluminum wedge is pres ent in only one radiograph and the difference image of the wedge in th e subtraction image is used to calculate the aluminum equivalent chang e in bone density. Pairs of standardized x-rays were taken with synthe tic bone chips of known weights placed when the second x-ray was taken . The volumetric change produced by the bone chips was calculated by t he two methods. The relationship of the calculated volumes to the chip weights had a higher r(2) value (P < 0.05) for the two-wedge method t han for the one-wedge method. The two-wedge method is recommended for volumetric quantification of alveolar bone change. The influence of th e clarity of the aluminum wedge image in the x-ray pairs was also exam ined in this study and found to be significant. Attention must be give n to factors which affect the aluminum wedge image characteristics to achieve optimal results.