Microwave Ablation: Comparison of Simultaneous and Sequential Activation of Multiple Antennas in Liver Model Systems

Abstract

Purpose:To compare microwave ablation zones created by using sequential or simultaneous power delivery in ex vivo and in vivo liver tissue. Materials and Methods:All procedures were approved by the institutional animal care and use committee. Microwave ablations were performed in both ex vivo and in vivo liver models with a 2.45-GHz system capable of powering up to three antennas simultaneously. Two-and three-antenna arrays were evaluated in each model. Sequential and simultaneous ablations were created by delivering power (50 W ex vivo, 65 W in vivo) for 5 minutes per antenna (10 and 15 minutes total ablation time for sequential ablations, 5 minutes for simultaneous ablations). Thirty-two ablations were performed in ex vivo bovine livers (eight per group) and 28 in the livers of eight swine in vivo (seven per group). Ablation zone size and circularity metrics were determined from ablations excised postmortem. Mixed effects modeling was used to evaluate the influence of power delivery, number of antennas, and tissue type. Results:On average, ablations created by using the simultaneous power delivery technique were larger than those with the sequential technique (P , .05). Simultaneous ablations were also more circular than sequential ablations (P = .0001). Larger and more circular ablations were achieved with three antennas compared with two antennas (P , .05). Ablations were generally smaller in vivo compared with ex vivo. Conclusion:The use of multiple antennas and simultaneous power delivery creates larger, more confluent ablations with greater temperatures than those created with sequential power delivery.q RSNA, 2015

Effects of Microwave Ablation on Arterial and Venous Vasculature after Treatment of Hepatocellular Carcinoma

“…Thus, our results are difficult to generalize to clinical trials that use singleantenna systems and deliver less energy to target tissues (28,29). There are methods to quantify thermal dose response in ex-vivo tissue to account for different energy delivery approaches, but data on the relationship with blood vessels are limited (30).…”

Microwave ablation in primary and secondary liver tumours: technical and clinical approaches

“…High-powered microwave ablation systems can create ablation zones exceeding 4 cm with internal temperature exceeding 150 °C, especially systems with multiple-antenna capability (15,31,60). These high temperatures and large sizes can inadvertently damage non-target structures, especially in peripheral hepatic tumors that often lay adjacent to the bowel, abdominal wall or diaphragm.…”

“…Prior ablations create charring, bleeding, tissue contraction and gas bubbles, which can make visualization of the remaining tumor and margins difficult. Simultaneous antenna activation using multiple antennas has been demonstrated to create larger, rounder and more confluent ablation zones in a fraction of the time due to the higher heating rate compared to sequentially activated antennas (60). This effect was seen even when controlled for total energy delivery over the ablation period.…”

Delineation of Post-Procedure Ablation Regions with Electrode Displacement Elastography with a Comparison to Acoustic Radiation Force Impulse Imaging

“…MWA can be performed with multiple antennas simultaneously to cover larger treated volumes, with additional benefits such as an improved heating rate while avoiding the risk of skin burns caused by the grounding pad used in radiofrequency ablation (RFA) procedures (Liang and Wang 2007; Qian et al 2012; Lubner et al 2013; Wells et al 2015; Harari et al 2016; Ziemlewicz et al 2016). Promising treatment outcomes were reported for solitary tumors less than 2 cm in diameter (Lencioni and Crocetti 2012; Shiina et al 2012), while more recent studies demonstrate that MWA was successful in treating tumors larger than 3 cm (Ziemlewicz et al 2015; Thamtorawat et al 2016; Ziemlewicz et al 2016).…”