Fractal dimension of bone texture in radiographs correlates to ultrasound broadband attenuation T-score.

Objectives: We aimed to measure the fractal dimension on x-ray images and ultrasonographic parameters of the os calcis of bone from 4 districts in osteoporotic patients and in control subjects, in order to test the hypothesis that ultrasonographic parameters correlate to the fractal dimension obtained on x-ray images.
Methods: Fractal analysis on radiological images from 4 bone districts (proximal femur, calcaneus, metacarpus and 3rd phalanx) was performed in a study comparing ultrasonographic evaluation of the os calcis in severe osteoporotic patients and in control cases. We studied 86 x-ray-views from patients with severe reduction of ultrasound Stiffness Index and in healthy women. Ultrasound measurements of left os calcis were performed using the Lunar Achilles-Plus instrument. Fractal analysis was performed using the box-counting method.
Results: In healthy subjects, fractal dimension, D, measure of structural complexity, resulted close to the topological dimension (no fractal structure), TD, in femur (1.99±0.03)and phalanx (1.96±0.03), D differed significantly from TD in calcaneus (D=1.90±0.02; p<0.001) and metacarpus (D=1.89±0.03, p<0.001). In osteoporotic subjects, in calcaneus and metacarpus, D was higher (1.94±0.03, 1.93±0.03, respectively) than in healthy subjects (1.90±0.02, 1.89±0.02, respectively, p<0.01). In all the subjects, fractal dimension and ultrasound broadband attenuation T-score correlated significantly in calcaneus and metacarpus (p<0.03 and p<0.02, respectively).
Conclusions: Parameters based on a combination of ultrasonic examination and fractal analysis on radiographic images may add useful structural information regarding the patients' skeleton using non invasive procedures.