Korean J Radiol.  2022 Jan;23(1):42-51. 10.3348/kjr.2021.0134.

Direction of Tissue Contraction after Microwave Ablation: A Comparative Experimental Study in Ex Vivo Bovine Liver

• Lee J
• Rhim H
• Lee MW
• Kang TW
• Song KD
• Lee JK

• KMID: 2523701
• DOI: http://doi.org/10.3348/kjr.2021.0134

Abstract

Objective
This study aimed to investigate the direction of tissue contraction after microwave ablation in ex vivo bovine liver models.
Materials and Methods
Ablation procedures were conducted in a total of 90 sites in ex vivo bovine liver models, including the surface (n = 60) and parenchyma (n = 30), to examine the direction of contraction of the tissue in the peripheral and central regions from the microwave antenna. Three commercially available 2.45-GHz microwave systems (Emprint, Neuwave, and Surblate) were used. For surface ablation, the lengths of two overlapped square markers were measured after 2.5- and 5-minutes ablations (n = 10 ablations for each system for each ablation time). For parenchyma ablation, seven predetermined distances between the markers were measured on the cutting plane after 5- and 10-minutes ablations (n = 5 ablations for each system for each ablation time). The contraction in the radial and longitudinal directions and the sphericity index (SI) of the ablation zones were compared between the three systems using analysis of variance.
Results
In the surface ablation experiment, the mean longitudinal contraction ratio and SI from a 5-minutes ablation using the Emprint, Neuwave, and Surblate systems were 28.92% and 1.04, 20.10% and 0.53, and 24.90% and 0.45, respectively (p < 0.001). A positive correlation between longitudinal contraction and SI was noted, and a similar radial contraction was observed. In the parenchyma ablation experiment, the mean longitudinal contraction ratio and SI from a 10-minutes ablation using the three pieces of equipment were 38.60% and 1.06, 32.45% and 0.61, and 28.50% and 0.50, respectively (p < 0.001). There was a significant difference in the longitudinal contraction properties, whereas there was no significant difference in the radial contraction properties.
Conclusion
The degree of longitudinal contraction showed significant differences depending on the microwave ablation equipment, which may affect the SI of the ablation zone.

Keyword

Microwave; Thermal ablation; Tissue contraction; Ablation zone shape; Sphericity index