Microwave ablation energy delivery: Influence of power pulsing on ablation results in an ex vivo and in vivo liver model. Issue 12 (18th November 2014)

• Record Type: Journal Article
• Authors: Bedoya, Mariajose; del Rio, Alejandro Muñoz; Chiang, Jason; Brace, Christopher L.
• Is Part Of: Medical physics. Volume 41:Issue 12(2014)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2014-11-18
• Subjects: biological tissues -- haemorheology -- liver -- microwave heating; Therapeutic applications -- Biothermics and thermal processes in biology -- Fluid transport and rheology; Radiation therapy -- Heating using microwaves; microwave ablation -- pulsed power -- continuous power -- temperature monitor; Tissue ablation -- Liver -- Microwaves -- Cancer -- Antennas -- Tissues -- Haemodynamics -- Radiofrequency power transmission -- Kidneys; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4901312
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: The purpose of this study was to compare the impact of continuous and pulsed energy deliveries on microwave ablation growth and shape in unperfused and perfused liver models. Methods: A total of 15 kJ at 2.45 GHz was applied to ex vivo bovine liver using one of five delivery methods ( n = 50 total, 10 per group): 25 W continuous for 10 min (25 W average), 50 W continuous for 5 min (50 W average), 100 W continuous for 2.5 min (100 W average), 100 W pulsed for 10 min (25 W average), and 100 W pulsed for 5 min (50 W average). A total of 30 kJ was applied to in vivo porcine livers ( n = 35, 7 per group) using delivery methods similar to the ex vivo study, but with twice the total ablation time to offset heat loss to blood perfusion. Temperatures were monitored 5–20 mm from the ablation antenna, with values over 60 °C indicating acute cellular necrosis. Comparisons of ablation size and shape were made between experimental groups based on total energy delivery, average power applied, and peak power using ANOVA with post‐hoc pairwise tests. Results: No significant differences were noted in ablation sizes or circularities between pulsed and continuous groups in ex vivo tissue. Temperature data demonstrated more rapid heating in pulsed ablations, suggesting that pulsing may overcome blood perfusion and coagulate tissues more rapidly in vivo . Differences in ablation size and shape were noted in vivo despite equivalent energy delivery among all groups. Overall, the largest ablation volume in vivo was produced with 100 W continuous for 5 min (265.7 ± 208.1 cm 3 ). At 25 W average, pulsed‐power ablation volumes were larger than continuous‐power ablations (67.4 ± 34.5 cm 3 versus 23.6 ± 26.5 cm 3, P = 0.43). Similarly, pulsed ablations produced significantly greater length ( P ≤ 0.01), with increase in diameter ( P = 0.09) and a slight decrease in circularity ( P = 0.97). When comparing 50 W average power groups, moderate differences in size were noted ( P ≥ 0.06) and pulsed ablations were again slightly more circular. Conclusions: Pulsed energy delivery created larger ablation zones at low average power compared to continuous energy delivery in the presence of blood perfusion. Shorter duty cycles appear to provide greater benefit when pulsing.