Quantifying Local Stiffness Variations in Radiofrequency Ablations With Dynamic Indentation

Abstract

Elastographic imaging can be used to monitor ablation procedures, however confident and clear determination of the ablation boundary is essential to ensure complete treatment of the pathological target. To investigate the potential for ablation boundary representation on elastographic images, local variations in the viscoelastic properties in radiofrequency ablated regions that were formed in vivo in porcine liver tissue were quantified using dynamic indentation. Spatial stiffness maps were then correlated to stained histology, the gold standard for determination of the ablation periphery or boundary. Regions of interest in eleven radiofrequency ablation samples were indented at 18–24 locations each, including the central zone of complete necrosis and more peripheral transition zones including normal tissue. Storage modulus and rate of stiffening were both greatest in the central ablation zone and decreased with radial distance away from the center. The storage modulus and modulus contrast at the ablation outer transition zone boundary were 3.1 ± 1.0 kPa and 1.6 ± 0.4, respectively, and 36.2 ± 9.1 kPa and 18.3 ± 5.5 at the condensation boundary within the ablation zone. Elastographic imaging modalities were then compared to gross pathology in ex vivo bovine liver tissue. Area estimated from strain, shear wave velocity, and gross pathology images were 470 mm2, 560 mm2, and 574 mm2, respectively, and ablation widths were 19.4 mm, 20.7 mm, and 23.0 mm. This study has provided insights into spatial stiffness distributions within radiofrequency ablations and suggests that low stiffness contrast on the ablation periphery leads to the observed underestimation of ablation extent on elastographic images.

Planar strain analysis of liver undergoing microwave thermal ablation using x‐ray CT

“…Ablation and desiccation of the tissue leads to protein denaturation which is known to result in an increase in the elastic modulus of the tissue. Accordingly, some methods for elastic modulus imaging, [12][13][14][15] stiffness, [16][17][18] and strain imaging 19 have demonstrated their potential in evaluating thermal ablation zones and potentially provide some added value to the clinicians. However, in addition to the imaging modality itself, these methods commonly require supplementary equipment or devices to enable the measurements of the elasticity and stiffness changes.…”

Visualizing ex vivo radiofrequency and microwave ablation zones using electrode vibration elastography

“…Isotropy is violated in the case of thermally ablated regions, as tissue density and stiffness change relative to untreated tissue following ablation. 34 In addition, wave reflections can affect wave speed estimation. 35,36 This may make stiffness estimation of thermal ablations with shear wave imaging qualitative, as with strain imaging.…”

Efficient 3-D Reconstruction in Ultrasound Elastography via a Sparse Iteration Based on Markov Random Fields

“…The smooth transition region was modeled using a sigmoid function. The width of this transition region was set to 5 mm following results from [32]. In reality, ablation shapes may be irregular due to presence of blood vessels in the vicinity.…”