BITEWING-BASED ALVEOLAR BONE DENSITOMETRY - DIGITAL IMAGING RESOLUTION REQUIREMENTS

The resolution requirements were determined for detection of increment al alveolar bone loss from digitized Ektaspeed radiographs. Ten clinic al radiographs were examined with a calibrated optical microscope to m easure the smallest feature of interest discernible for alveolar bone. Images of trabeculae >100 mum in diameter could be identified, but sm aller ones could not be resolved. The Nyquist Criterion requires sampl ing with 500 mum (or smaller) pixels to measure such features. Numerou s 25 mum Ag aggregates were present. Fifty mum resolution is a practic al compromise between noise level and feature resolution. In another e xample of 10 bitewings digitized at 8 bit grey scale, about half the a vailable range was used for alveolar bone, resulting in uncertainty, o ver a range of 2 optical density (OD) units, of about 1.42% at the ave rage OD for alveolar bone (1.1). With the same radiographs digitized a t 12 bit resolution, over 2000 of 4096 grey scales were used with a co rresponding uncertainty of about 0.09%. Twelve-bit precision was also able to resolve smaller increments in an aluminium stepwedge than was 8 bit precision. Twelve-bit grey scale and 50 mum spatial resolution a re recommended for alveolar bone densitometry performed with Ektaspeed radiographs.