Evaluation of tissue deformation during radiofrequency and microwave ablation procedures: Influence of output energy delivery

Abstract

Purpose The purpose of this study was to quantitatively analyze tissue deformation during radiofrequency (RF) and microwave ablation for varying output energy levels. Methods A total of 46 fiducial markers which were classified into outer, middle, and inner lines were positioned into a single plane around an RF or microwave ablation applicator in each ex vivo bovine liver sample (8 cm × 6 cm × 4 cm, n = 18). Radiofrequency (500 kHz; ~35 W average) or microwave (2.4 GHz; 50–100 W output, ~35–70 W delivered) ablation was performed for 10 min (n = 4–6 each setting). CT images were acquired over the entire liver volume every 15 s. Principle strain magnitude and direction were determined from fiducial marker displacement. Normal and shear strain were then calculated such that negative strain denoted contraction and positive strain denoted expansion. Temporal variations, the final magnitudes, and angles of the strain were compared across energy delivery settings, using one‐way ANOVA with post hoc Tukey's tests. Results On average, tissue strain rates peak at around 1 min and decayed exponentially over time. No evidence of tissue expansion was observed. The tissue strains from RF and 50 W, 75 W, and 100 W microwave ablation at 10 min were −8.5%, −38.9%, −54.4%, and −65.7%, respectively, from the inner region and −3.6%, −23.7%, −41.8%, and −44.3%, respectively, from the outer region. Negative strain magnitude was positively correlated to energy delivery in the inner region (Spearman’s ρ = −0.99). Microwaves at higher powers (75–100 W) induced significantly more strain than at lower power (50 W) or after RF ablation (P < 0.01). Principal strain angles ranged from 0.8° to −8.1°, indicating that tissue deformed more in the direction transverse to the applicator than along the direction of the applicator. Conclusions The influence of output energy on tissue deformation during RF and microwave ablation was analyzed. Microwave ablation created significantly greater contraction than RF ablation with similar energy delivery. During microwave ablation, more contraction was noted at higher power levels and in proximity to the antenna. Contraction primarily transverse to the antenna produces ablation zones that are more elongated than the original tissue volume.

Small single perivascular hepatocellular carcinoma: comparisons of radiofrequency ablation and microwave ablation by using propensity score analysis

“…HR, hazard ratio; CI, confidence intervals; OS, overall survival; DFS, disease-free survival; HBV, hepatitis B virus; HCV, hepatitis C virus; CTP, Child-Turcotte-Pugh; ALBI, albumin-bilirubin; AFP: αfetoprotein; ALB: albumin; TBIL: total bilirubin; AST, aspartate aminotransferase; ALT, alanine aminotransferase; PV, portal vein; HV, hepatic vein; RFA, radiofrequency ablation of residual tumor following RFA, and this could manifest as early LTP during follow-up. While the technical characteristics of RFA and MWA are quite similar, they exhibit several differences in their physical mechanisms of thermogenesis [22][23][24]. The significant difference is that during RFA, heat is confined to zones of high current density, while during MWA, it is generated in a fixed space around the antenna applicator.…”

Thermal ablation of biological tissues in disease treatment: A review of computational models and future directions

“…The proposed simulation model showed a good agreement of the temperature and contraction-induced displacement with the experimental in vitro results. More recently, (Liu and Brace, 2019) reported an experimental study on bovine liver to quantitatively analyze the tissue deformation during RFA and MWA. It was reported that the tissue dimensions contracted by 5% post RFA and 20-65% post MWA procedures.…”

Image‐guided percutaneous microwave ablation of early‐stage non–small cell lung cancer

“…MWA has some potential advantages over RFA including faster ablations, higher temperature which is not limited by electric impedance, less sensitivity to tissue types with more consistent results, relatively insensitivity to “heat sinks,” and ability to create much larger ablation zones. For lesions larger than 3 cm, particularly those over 5 cm, MWA is significantly better than RFA 18‐22 . Furthermore, multiple MWA antennas can be positioned into target lesions and activated simultaneously, which maximizes nearly spherical ablation zone 23 .…”

“…For lesions larger than 3 cm, particularly those over 5 cm, MWA is significantly better than RFA. [18][19][20][21][22] Furthermore, multiple MWA antennas can be positioned into target lesions and activated simultaneously, which maximizes nearly spherical ablation zone. 23 Lung ablation zone was reported as large as 54.8 ± 8.5 mm (mean ± SD) in animal studies.…”