Frequency and resolution dependence of the anisotropic impedance estimation in cortical bone using time-resolved scanning acoustic microscopy.
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.
Department of Orthopedics, Q-BAM Group, Martin Luther University of Halle-Wittenberg, 06097 Halle, Germany. kay.raum@medizin.uni-halle.de
Kay
K
Raum
Jan
J
Reisshauer
Jörg
J
Brandt
D000328:Adult; D000368:Aged; D016880:Anisotropy; D001842:Bone and Bones / Q000737:chemistry* / Q000166:cytology* / Q000000981:diagnostic imaging; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D033401:Microscopy, Acoustic; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis; D013223:Statistics as Topic; D013696:Temperature