SPATIAL-RESOLUTION AND ANGULAR ALIGNMENT TOLERANCE IN RADIOMETRIC ANALYSIS OF ALVEOLAR BONE CHANGE

THIS PILOT STUDY WAS UNDERTAKEN to determine the effect of x-ray beam alignment and spatial resolution on quantification of alveolar bone us ing radiometric techniques. Six (6) dry mandibles were radiographed at 70 kVp, 10 mA, 0.6 seconds using D-speed film, with a bone chip (2.64 , 4.10, or 6.07 mg) present or absent at 7 x-ray beam alignments (0 de grees, 2 degrees horizontal, 2 degrees vertical, 4 degrees horizontal, 4 degrees vertical, 6 degrees horizontal, 6 degrees vertical). This r esulted in 28 radiographs per mandible. Radiographs were digitized usi ng 50- and 200-mu m pixel spatial resolution. Image gray levels were s tandardized using a simple look-up table shift. Regions of interest (R OIs) were positioned on the alveolar bone where the bone chips had bee n placed. Cumulative percent histograms (CPH) were calculated for thos e ROIs. Regression analysis was used to evaluate the relationships bet ween CPH changes and bone chip size as x-ray beam angulation and spati al resolution was varied. The resulting R(2) values for angulation ran ges of 0 degrees to 1.4 degrees, 1.5 degrees to 2.4 degrees, and 2.5 d egrees to 5.5 degrees were: 0.983, 0.941, 0.891 for 50-mu m pixel imag es and 0.869, 0.909, and 0.774 for 200-mu m pixel images. We conclude that 50-mu m pixel spatial resolution is apparently superior to 200-mu m pixel images if radiometric data is to be evaluated. With 50-mu m p ixel spatial resolution, alignment variations up to 5 degrees may be a cceptable in clinical studies, depending on the magnitude of bone chan ge that is to be detected.