Frequency and resolution dependence of the anisotropic impedance estimation in cortical bone using time‐resolved scanning acoustic microscopy

Abstract

The influences of frequency and spatial resolution on the anisotropic impedance estimation of cortical bone was investigated in the frequency range 25-100 MHz. A set of spherically focused transducers provided a spatial resolution in the range from 150 down to about 20 mum. Four embedded cortical bone samples (two male, two female, two donors aged <30 years, two donors aged >70 years) were cut with different orientations relative to the long axis of the femur (0-90 degrees ). From each section, impedance maps were acquired in the C-scan mode. Histogram evaluations showed a similar angular dependence with a characteristic off-axis maximum of the estimated impedance for all samples and frequencies. The impedance values obtained with the 25-MHz transducer were significantly lower than those obtained with the 50- and 100-MHz transducers. Morphological parameters of the macrostructure, for example, size and distribution of the haversian channels and the resulting porosity, were estimated from the high-resolution acoustic images. These structures appeared to have a significant influence on the measured properties of the bone matrix for the low-frequency and low-aperture measurements.

Spatial distribution of tissue level properties in a human femoral cortical bone

“…The principles of the acoustic data acquisition and the conversion of the measured reflection amplitude to acoustic impedance and elastic coefficients have been described elsewhere (Lakshmanan et al, 2007;Raum et al, 2003Raum et al, , 2004Raum, 2008) and are summarized in the appendix.…”

Apparent Young's modulus of human radius using inverse finite-element method

“…This remain true when cortical thickness is less than that required for testing samples machining, but the techniques do not take into account porosity. Moreover, they are extremely sensitive to the region where the test is carried out (Zysset et al, 1999), due to their high resolution from a few mm for SAM (Raum et al, 2004) down to 1 mm for latest indenter (Turner et al, 1999). It may be possible to infer the apparent Young's modulus from such measurements performed at the microscopic level.…”

Local ultrasonic wave velocities in trabeculae measured by micro-Brillouin scattering

“…Therefore measurements of microscopic elastic properties of bone have been made with in vitro measurement methods, such as nanoindentation and scanning acoustic microscopy (SAM). [8][9][10][11][12][13] These methods can provide information on the elastic modulus, hardness, and acoustic impedance in small areas of bone. These methods especially provide information originating from the direction perpendicular to the specimen surface.…”