Influence of histochemical preparation on acoustic parameters of liver tissue: a 5-MHz study

In this study the influence of various histological techniques on the acoustic parameters of liver tissue was investigated. Radiofrequency (RF) echographic data were obtained in vitro from 21 liver samples taken from 8 white New Zealander rabbits. The samples were measured in four different subsequent histological tissue processing conditions (freshly excised, 4% buffered formalin fixed, after it went through a paraffin cycle and after staining with hematoxylin and eosin). The acoustic parameters that were obtained from the rf data were velocity of sound, slope of the attenuation coefficient versus frequency between 1.9 and 6.9 MHz, attenuation coefficient at 4.4 MHz, slope of the backscattering spectrum between 1.9 and 6.9 MHz, and intercept of the backscattering spectrum. It was found that fixation by formalin preserves the acoustic properties of the tissue to a reasonable extent. Embedding in paraffin and deparaffinizing induces large changes in the acoustic properties of the tissue. As an alternative, freezing prior to cutting, rather than the paraffin cycle, was investigated also in 10 liver samples obtained from 4 New Zealander rabbits. This method produced no significant changes of the acoustic parameters and should therefore be preferred in acoustic microscopy.