ASSESSING THE DEGREE OF OSTEOPOROSIS IN THE AXIAL SKELETON USING THE DEPENDENCE OF THE FRACTAL DIMENSION ON THE GREY LEVEL THRESHOLD

Combining the measurement of bone mineral density (BMD) and the classi fication of the trabecular structure in cancellous bone improves the e stimation of the degree of osteoporosis. A fractal method for the auto matic quantitative classification of the trabecular structure in midve rtebral slices of lumbar vertebrae is introduced. This method is based on the computation of the fractal dimension (box controlling method) for varying binarization thresholds. Radiographic images from 30 lumba r vertebrae and CT images from an additional 16 lumbar vertebrae were analysed by calculating the dimension D in dependency of the threshold value T. The function D(T) was normalized by the average image grey v alue, eliminating the bone mineral density from the computations. The results show that ?he images of the lumbar vertebrae have fractal prop erties, and the function (T) has a typical behaviour that allows the d iscrimination of the degree of osteoporosis. With two parameters extra cted from the function D(T) the correlation coefficients with BMD were both -79% for the radiographic images, and -53% and -91% for the CT d ata, respectively.