Alterations in Ultrasound Scattering Following Thermal Ablation in ex vivo XXXX Liver.

@entity82 @entity1560 @entity5 @entity409 @entity3626 @entity291
UNASSIGNED: Thermal ablation is a minimally invasive @entity5 treatment which has been rapidly gaining clinical acceptance. It is well known that thermal ablation increases the acoustic attenuation and shear modulus of tissue. In this work, we examine changes to the spatial distribution of scatterers in liver tissue following thermal ablation. Acoustic scatterers within liver tissue have frequently been modeled as pseudo-periodic. The positions of pseudo-periodic scatterers have been Gamma distributed along the beam dimension, and these scatterers are characterized by their @entity3626 ( @entity3626 ). Prior work have demonstrated significant changes in @entity3626 due to diffuse @entity409 , such as @entity1560 progressing to @entity82 . However, relatively few results have been reported regarding changes in @entity3626 following thermal ablation. In this study, we estimated @entity3626 in ex vivo @entity291 liver by detecting local maxima in spectral coherence functions calculated using Thomson's multi-taper method. We examined a large number of uncorrelated regions of interest recorded from five normal @entity291 livers (~300 images from each animal). We also examined a large number of ROI's from five @entity291 livers following thermal coagulation. All @entity291 livers were obtained from a commercial meat production facility immediately following animal sacrifice and imaged within 12 hours. Thermal coagulation was induced by heating liver in saline water baths at 80   C for 45 minutes. For normal, unheated liver an @entity3626 of approximately 1.5 mm was estimated. Following thermal ablation, an @entity3626 of approximately 0.5 mm in thermally coagulated tissue was obtained. Frequently, studies estimating @entity3626 in liver tissue provide an @entity3626 estimate regardless of the state of tissue. Authors rarely present what their @entity3626 estimation algorithm would produce if it were applied to tissue which is better modeled as a collection of uniformly, randomly distributed scatterers lacking periodicity. In this study, we found that thermal coagulation results in a loss of periodicity. The @entity3626 of 0.5 mm corresponds to the value that a spectral coherence-based @entity3626 algorithm would produce if presented with a signal that was generated from uniform, randomly distributed scatterers.
