Broadband Ultrasound Attenuation (BUA) is one of the most widely used ultrasound parameters for assessing bone properties. However, its application is limited by its definition, which requires a linear relationship between ultrasound attenuation and frequency in order to reliably calculate the slope of the fitted curve. BUA performs well with regularly shaped bones such as the calcaneus but is less effective for other bone structures. Frequency-modulated ultrasound, on the other hand, concentrates acoustic energy within a designated frequency band, making it an ideal signal for studying the frequency response of bone to ultrasound. Two independent studies have demonstrated that this approach shows strong potential for characterizing bone properties.
The first study [1] investigated the efficacy of frequency-modulated ultrasound signals compared with BUA. Twenty-one trabecular bone cubes were harvested from sheep femoral condyles, with cube axes aligned to the anatomical superior–inferior (SI), anterior–posterior (AP), and medial–lateral (ML) orientations. Micro-CT analysis was performed on each sample to obtain bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp). Ultrasound testing was conducted along the three orthogonal orientations using both pulse and frequency-modulated ultrasound. Comparisons between frequency-modulated attenuation (FMA) and broadband ultrasound attenuation (BUA) were carried out within the 300–700 kHz frequency range. Results showed that FMA demonstrated stronger correlations with trabecular structural parameters in the SI orientation (R² = 0.84 for BV/TV, R² = 0.77 for Tb.Th, R² = 0.70 for Tb.Sp) compared to BUA (R² = 0.30 for BV/TV, R² = 0.27 for Tb.Th, R² = 0.33 for Tb.Sp). In the AP orientation, FMA showed a higher correlation with Tb.Sp (R² = 0.64) than BUA (R² = 0.48), but relatively lower correlations with BV/TV (R² = 0.48) and Tb.Th (R² = 0.31) compared to BUA (R² = 0.64 for BV/TV, R² = 0.58 for Tb.Th). These findings suggest that FMA may serve as a promising new ultrasound index for assessing bone properties.
The second study [2] examined the efficacy of frequency-modulated ultrasound attenuation for assessing trabecular structural properties across four frequency bands centered at 500 kHz, 900 kHz, 1.3 MHz, and 1.7 MHz, each with a bandwidth of 400 kHz. Five trabecular cubes (1 cm³) were harvested from fresh bovine distal femurs. To increase the variability in structural properties and thus improve correlation analysis, each cube underwent four sequential demineralization steps, expanding the sample size to 25. Pearson correlation analysis was then performed between ultrasound attenuation in the four frequency bands and trabecular structural parameters. The results demonstrated that the correlations between frequency-modulated ultrasound attenuation and trabecular properties were frequency-band dependent. In the proximal–distal orientation, attenuation showed the strongest correlation with BV/TV (R² = 0.73, p < 0.001) and trabecular thickness (R² = 0.50, p < 0.001) at the 1.7 MHz band. Correlations with trabecular number (mean R² = 0.80, p < 0.001) and trabecular separation (mean R² = 0.83, p < 0.001) were consistently strong across all frequency bands. In the anterior–posterior orientation, attenuation correlated most strongly with BV/TV (R² = 0.80, p < 0.001) and trabecular thickness (R² = 0.71, p < 0.001) at the 1.3 MHz band. Attenuation in the 500 kHz band was most sensitive to trabecular number (R² = 0.71, p < 0.001) and trabecular separation (R² = 0.80, p < 0.001). In contrast, no significant correlations were observed in the medial–lateral orientation across any of the frequency bands.
- Lin W., Xia Y, Qin Y, Characterization of the trabecular bone structure using frequency modulated ultrasound pulse, Journal of Acoustic Society of America, 125(6), 4071-4077, June 2009
- Lin, W., Serra-Hsu, F., Cheng, J, Frequency Specific Ultrasound Attenuation Is Sensitive to Trabecular Bone Structure, Ultrasound in Medicine and Biology, 38, No. 12, p2198-2207, 2012