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

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. 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). 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.