Anisotropy of high-frequency integrated backscatter from aortic valve cusps.

The biaxial anisotropy of integrated backscatter from aortic valve cusps was characterized ex vivo as an initial assessment of the suitability of high-frequency ultrasound for nondestructive evaluation of fiber alignment in tissue-engineered heart valves. Apparent integrated backscatter (AIB) from eight fresh, intact porcine cusps was measured over an 80 degrees range of insonification angles using a 40-MHz ultrasound system. Angular dependence of backscatter was characterized by fitting a sinusoid to plots of AIB versus insonification angle for data acquired while rotating the transducer about the cusps in the circumferential and radial directions. Angular variations in backscatter were detected along both directions in individual specimens, although the mean amplitude of the fitted sinusoid was significantly greater for the circumferential data (12.1 +/- 2.6 dB) than the radial data (3.5 +/- 3.1 dB, p = 0.002). The higher angular variation of backscatter in the circumferential direction implies that collagen fibers in the fibrosa layer are the most prominent source of high-frequency scattering from porcine aortic valve cusps. The ability to characterize anisotropic backscattering from individual specimens demonstrates that high-frequency ultrasound can be used for nondestructive evaluation of fiber alignment in heart valve biomaterials.