Stiffness distribution in the ablated zone after radiofrequency ablation for liver: An ex-vivo study with a tissue elastometer.

OBJECTIVE: To investigate the stiffness distribution in the ablated zone after radiofrequency ablation (RFA), we used a device called tissue elastometer based on gross liver samples.

MATERIALS: AND METHODS: Twelve freshly excised porcine livers were subject to RFA under a same setup to form elliptic ablated samples. Each sample was cut open for gross examination, and then the surface of the section plane was sliced into one piece for Young's modulus test using the tissue elastometer. Five test points along the long- and short-axis on each piece were selected to evaluate stiffness distribution respectively. Among them, four points distributed equidistantly from center to boundary in the ablated zone and one was in the unablated zone.

RESULTS: In the ablated zone, we found the Young's moduli were significantly different among the four test points both in long- (F = 99.04, p <0.001) and short-axis (F = 79.47, p <0.001) directions. The Young's modulus showed a downtrend in each direction, and was linearly related to the distance from the center to the test point (for long axis, R2 = 0.968; for short axis, R2 = 0.984, both p <0.001). A more significant downtrend was observed in short-axis direction. The Young's moduli gained from the inner edge of ablated zone were comparable and significantly higher than those from the outer edge for both directions. The maximum value of 24.71kPa for Young's modulus was the appropriate threshold to ensure the tissues were necrotic completely.

CONCLUSION: The stiffness inside the ablated zone represented a radial distribution with downtrend, following a linear law. The stiffness at the inner edge of ablated zone is stable and significantly higher than that at the outer edge. The maximum value of 24.71 kPa close to the inner edge of Wz may be used as the standard of complete ablation.