title: Experimental measurement of microwave ablation heating pattern and comparison to computer simulations.
abstract: For computational models of microwave ablation (MWA), knowledge of the antenna design is necessary, but the proprietary design of clinical applicators is often unknown. We characterised the specific absorption rate (SAR) during MWA experimentally and compared to a multi-physics simulation.
  
  
  
  An infrared (IR) camera was used to measure SAR during MWA within a split ex vivo liver model. Perseon Medical's short-tip (ST) or long-tip (LT) MWA antenna were placed on top of a tissue sample (n = 6), and microwave power (15 W) was applied for 6 min, while intermittently interrupting power. Tissue surface temperature was recorded via IR camera (3.3 fps, 320 × 240 resolution). SAR was calculated intermittently based on temperature slope before and after power interruption. Temperature and SAR data were compared to simulation results.
  
  
  
  Experimentally measured SAR changed considerably once tissue temperatures exceeded 100 °C, contrary to simulation results. The ablation zone diameters were 1.28 cm and 1.30 ± 0.03 cm (transverse), and 2.10 cm and 2.66 ± -0.22 cm (axial), for simulation and experiment, respectively. The average difference in temperature between the simulation and experiment were 5.6 °C (ST) and 6.2 °C (LT). Dice coefficients for 1000 W/kg SAR iso-contour were 0.74 ± 0.01 (ST) and 0.77 (± 0.03) (LT), suggesting good agreement of SAR contours.
  
  
  
  We experimentally demonstrated changes in SAR during MWA ablation, which were not present in simulation, suggesting inaccuracies in dielectric properties. The measured SAR may be used in simplified computer simulations to predict tissue temperature when the antenna geometry is unknown.
authors.affiliation: a Department of Diagnostic Imaging , Rhode Island Hospital , Providence , Rhode Island , USA.
authors.forename: Garron
authors.initials: G
authors.lastname: Deshazer
authors.affiliation: b Department of Electrical and Computer Engineering , Kansas State University , Manhattan , Kansas , USA.
authors.forename: Punit
authors.initials: P
authors.lastname: Prakash
authors.affiliation: a Department of Diagnostic Imaging , Rhode Island Hospital , Providence , Rhode Island , USA.
authors.forename: Derek
authors.initials: D
authors.lastname: Merck
authors.affiliation: c Department of Pediatrics , Medical University of South Carolina , Charleston , South Carolina , USA.
authors.forename: Dieter
authors.initials: D
authors.lastname: Haemmerich
mesh_terms: D055011:Ablation Techniques; D000818:Animals; D003198:Computer Simulation; D008099:Liver / Q000601:surgery; D008872:Microwaves; D008954:Models, Biological; D013552:Swine; D013696:Temperature
keywords: Ablation modelling; bio-heat transfer; microwave ablation; specific absorption rate; treatment planning