Fractal dimension predicts broadband ultrasound attenuation in stereolithography models of cancellous bone

There has been considerable debate on the relative dependence of broadband ultrasound attenuation (nBUA, dB MHz(-1) cm(-1)) upon the density and structure of cancellous bone. A nonlinear relationship between nBUA and porosity has recently been demonstrated using stereolithography models, indicating a high structural dependence for nBUA. We report here on the measurement of trabecular perimeter and fractal dimension on the two-dimensional images used to create the stereolithography models. Adjusted coefficients of determination (R2) with nBUA were 94.4% (p < 0.0001) and 98.4% (p < 0.0001) for trabecular perimeter and fractal dimension respectively. The feature of fractal dimension representing both the porosity and connectivity of a given structure is most exciting. Further work is required to determine the relationship between broadband ultrasound attenuation and fractal dimension in complex three-dimensional cancellous bone structures.