Effects of tissue anisotropy on the spectral characteristics of ultrasonicbackscatter measured with a clinical imaging system

In this paper, we report the effects of inherent tissue anisotropy on the s pectral properties of backscattered ultrasound when measured with a commerc ially-available imaging system. We insonified five specimens of bovine tend on immersed in a water tank and rotated in 10 degrees increments while bein g imaged with a Hewlett-Packard Sonos 1500 system. The backscattered RF sig nals corresponding to each angle of insonification were digitized and the s pectral characteristics of the backscattered ultrasound were determined. Th e mean anisotropy, defined as the average difference between values at perp endicular and parallel insonification, for band-limited estimates of backsc attered power, centroid frequency, up per-band to lower-band power ratio, a nd upper-band to total-band power ratio were found to be 24.6 +/- 1.1 dB, 1 42 +/- 27 kHz, 32 +/- 13%, and 22 +- 5%, respectively (mean +/- SE). The ma gnitude of each of these backscatter spectral parameters was larger at perp endicular insonification compared with the corresponding values at parallel insonification, consistent with previous measurements of the inherent anis otropy of ultrasonic attenuation and backscatter in tissue.