Reconsidering the Layer Thickness Distribution in Aortic Valve Cusps Using High-Frequency Ultrasound
Zamir Khan^1,2, Derek R. Boughner^1,2,3, and James C. Lacefield^1,2
1University of Western Ontario, London, ON, Canada
²Robarts Research Institute, London, ON, Canada
³London Health Sciences Centre, London, ON, Canada
IEEE, June 2007

• > A non-destructive high-frequency ultrasound method for measuring the thickness of thin tissue layers was adapted to map the thicknesses of the fibrosa, spongiosa, and ventricularis layers of aortic valve cusps. The sound speed and layer thicknesses of thirteen porcine aortic valve cusps were measured. The measurements yielded results of (mean ± standard deviation) 0.81 ± 0.13 mm, 0.30 ± 0.07 mm, 0.23 ± 0.05 mm, and 0.32 ± 0.08 mm for the total, fibrosa, spongiosa, and ventricularis thicknesses, respectively, and a sound speed of 1527 ± 33 m/s. The uncertainty introduced by variations in sound speed plays a relatively small role in the variability of the thickness measurements. The relative distribution of layer thicknesses of fresh, intact cusps measured with this method differs from that of fixed, sliced cusps measured with conventional methods. Conclusion: This study demonstrates that high-frequency ultrasound can be used to provide non-destructive estimates of total thickness and layer thicknesses across nearly the entire surface area of aortic valve cusp specimens. The uncertainty of the exact sound speed in the cusp tissue appears to have little influence on thickness results. The ultrasound method yields different results for relative layer thicknesses from previously published measurements on fixed, sliced specimens. Because it does not require the tissue fixation or sectioning needed for conventional measurement methods, the ultrasound technique is expected to provide a useful tool for non-destructive evaluation and improvement of bioprosthetic and tissue-engineered heart valves.