The microanalyzer

Bone Mass Determination from Microradiographs by Computer-Assisted Videodensitometry

The mass of hard-tissue specimens is assessed by optimised microradiography followed by computer-assisted videodensitometry. Radiographs are produced with 27 kV roentgen radiation, filtered through 0.5 to 1 mm of aluminium, on high-resolution glass plates. Aluminium step wedges are used for density calibration, the result being expressed as ‘aluminium equivalent mass’. The plates are subjected to digital image analysis by an operator in interaction with a computer-based image processor, a television camera being used for image input. The program stored in the computer provides calibration of geometry and—via the stepwedge images—of densitometry, background adjustment, etc. Measurement takes place by integration over the specimen-image area. No assumptions being needed concerning a specific attenuation model, the errors stemming from the common presumption of exponential attenuation are eliminated. Density profiles or maps of mass distribution are readily obtained from the computer. From measurements of aluminium phantom samples, the total random error (coefficient of variation) was determined at 1.8 per cent, the microradiographic and videodensitometric procedures contributing 1.6 per cent and 0.9 per cent, respectively, whereas the systematic error was negligible. Since specimens need not be sectioned, this method does not interfere with subsequent histologic preparation.