Influence of signal selection on ultrasonic backscatter and in cancellous bone assessment

The goal of this study is to investigate the influence of the signal of interest (SOI) selection on ultrasonic backscatter coefficients and in cancellous bone evaluation. In-vitro backscatter measurements were carried out with 16 pieces of bovine cancellous bones at a central frequency of 5 MHz. The backscatter SOI was selected by a rectangle window (time length referred as T2) after an excluded volume (referred as T1). With varying T1 and T2 separately, the apparent backscatter coefficients (ABC) and its correlation to cancellous bone microstructure (bone volume fraction (BV/TV) and trabecular spacing (Tb.Sp)) were calculated. The results showed that the ABC decreased with increasing T1. The T2 had little influence on the ABC. In addition to affecting the measured values of ABC, the SOI selection also influenced the correlations between the ABC and structural parameters of cancellous bone. Significant positive correlations for ABC vs. BV/TV were observed for short T1 (<;1 μs) while strong negative correlations were observed when T1 increased to an enough long value (>3 μs). In contrast, strong negative correlations for ABC vs. Tb.Sp were observed when T1 was short (<;1 μs) while positive correlations were observed when T1 was long (>2 μs). The correlation coefficients fluctuated with T2 when T2 was short (<; 3 μs). This study demonstrated that the backscatter signal selection has a significant influence on cancellous bone assessment.