BITEWING-BASED ALVEOLAR BONE DENSITOMETRY - DIGITAL IMAGING RESOLUTION REQUIREMENTS

The resolution requirements were determined for detection of incremental alveolar bone loss from digitized Ektaspeed radiographs. Ten clinical radiographs were examined with a calibrated optical microscope to measure the smallest feature of interest discernible for alveolar bone. Images of trabeculae >100 mum in diameter could be identified, but smaller ones could not be resolved. The Nyquist Criterion requires sampling with 500 mum (or smaller) pixels to measure such features. Numerous 25 mum Ag aggregates were present. Fifty mum resolution is a practical compromise between noise level and feature resolution. In another example of 10 bitewings digitized at 8 bit grey scale, about half the available range was used for alveolar bone, resulting in uncertainty, over a range of 2 optical density (OD) units, of about 1.42% at the average OD for alveolar bone (1.1). With the same radiographs digitized at 12 bit resolution, over 2000 of 4096 grey scales were used with a corresponding 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 are recommended for alveolar bone densitometry performed with Ektaspeed radiographs.