Ability of Ultrasonic Apparent Backscatter to Reflect Cancellous Bone Densities

Abstract

The goal of this study was to investigate the ability of ultrasonic apparent backscatter to reflect cancellous bone densities, including the apparent density (App. D), bone organic density (BOD) of porous bones, and the material density (Mater. D) of trabeculae. Previous studies were mainly focused on the relationship between backscatter and bone mineral density (BMD). Thirty-five cuboid cancellous bone specimens (approximately 2.0 × 2.0 × 1.5 cm) were prepared from the distal end of bovine femur. In vitro ultrasonic backscatter signals were measured with a 2.25 MHz transducer and spatially scanning was performed for each specimen. The apparent integrated backscatter (AIB), frequency slope of apparent backscatter (FSAB) and frequency intercept of apparent backscatter (FIAB) were calculated with different backscatter signal of interests (SOIs), i.e. different delayed amount (T1) and selected amount (T2). The results showed that the apparent backscatter was significantly correlated to the bone volume fraction (BV/TV) (|R| up to 0.79, p < 0.05). Besides reflecting the microstructure of cancellous bone, the apparent backscatter parameters were also sensitive to bone densities. With proper T2 (1–7 μs), the AIB, FSAB and FIAB were significantly correlated with BOD, App. D and Mater. D (|R| = 0.51–0.82, p < 0.05). The results also showed that the backscatter signal of interest selection influenced cancellous bone evaluation. This study demonstrated that the backscatter has the ability to reflect bone apparent density and organic density, which cannot be provided by the X-ray densitometries. The assessment of bone densities helps to evaluate bone status comprehensively. This study suggested that ultrasonic backscatter could play a greater role in cancellous bone evaluation.