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Research Papers

Feasibility Assessment of Microwave Ablation for Treating Esophageal Varices

[+] Author and Article Information
Jan Sebek

Department of Electrical and Computer Engineering,
Kansas State University,
Manhattan, KS 66506;
Department of Circuit Theory,
Faculty of Electrical Engineering,
Czech Technical University in Prague,
Technicka 2,
Praha 6 166 27, Czech Republic
e-mail: sebekja4@fel.cvut.cz

Sergio Curto

Department of Electrical and Computer Engineering,
Kansas State University,
Manhattan, KS 66506
e-mail: s.curto@erasmusmc.nl

Jimmy Eaton-Evans

School of Engineering and Informatics,
NUIG,
Galway H91 TK33, Ireland
e-mail: jeaton-evans@nuigalway.ie

Jonathan Bouchier-Hayes

School of Engineering and Informatics,
NUIG,
Galway H91 TK33, Ireland
e-mail: Jonathan.BouchierHayes@bioinnovate.ie

Giuseppe Ruvio

School of Engineering and Informatics,
NUIG,
Galway H91 TK33, Ireland
e-mail: giuseppe.ruvio@nuigalway.ie

Chanran Ganta

Department of Diagnostic Medicine and Pathobiology,
Kansas State University,
1800 Denison Avenue,
Manhattan, KS 66506
e-mail: ckganta@vet.ksu.edu

Warren Beard

Department of Clinical Sciences,
Kansas State University,
1800 Denison Avenue,
Manhattan, KS 66506
e-mail: wbeard@ksu.edu

Navtej Buttar

Division of Gastroenterology and Hepatology,
Mayo Clinic,
200 1st Street SW,
Rochester, MN 55905
e-mail: buttar.navtej@mayo.edu

Louis Wong Kee Song

Division of Gastroenterology and Hepatology,
Mayo Clinic,
200 1st Street SW,
Rochester, MN 55905
e-mail: wong.louis@mayo.edu

Punit Prakash

Department of Electrical and Computer Engineering,
Kansas State University,
Manhattan, KS 66506
e-mail: prakashp@ksu.edu

1Corresponding author.

Manuscript received January 19, 2017; final manuscript received June 19, 2017; published online July 18, 2017. Assoc. Editor: Rafael V. Davalos.

J. Med. Devices 11(3), 031013 (Jul 18, 2017) (8 pages) Paper No: MED-17-1013; doi: 10.1115/1.4037187 History: Received January 19, 2017; Revised June 19, 2017

Esophageal varices are a significant complication of portal hypertension. Endoscopic variceal ligation (EVL) is one of the clinical standards for treating these varices and preventing their hemorrhage. Limitations of EVL include the risk of stricture formation and postband ulcer bleeding due to the damage caused to the esophageal mucosa, as well as the need for multiple endoscopic treatment sessions to eradicate the varices. The goal of this study is to develop a device and evaluate the technical feasibility of microwave ablation to seal esophageal varices, while preventing thermal damage to the surface mucosal tissue. A microwave applicator with a directional radiation pattern was developed for endoscopic ablation of esophageal varices. Electromagnetic and bioheat transfer computational models were employed to optimize the design of the microwave applicator and evaluate energy delivery strategies for this application. Experiments in ex vivo and in vivo tissue were employed to verify simulation results. Simulations predicted enhanced heating performance of the antenna using an angled monopole radiating element. Further, simulations indicate that while the endoscopic cap attenuated electric fields in tissue, it also enhanced surface cooling of tissue, increasing the likelihood of preserving mucosal tissue. Experiments in ex vivo tissue indicated the feasibility of sealing veins with 77 W microwave power delivered for 30 s. In vivo experiments demonstrated the ability to seal veins, while preserving surface tissue. This study demonstrated the technical feasibility of microwave thermal ablation for treating esophageal varices using a 2.45 GHz water-cooled directional microwave applicator.

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Figures

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Fig. 1

Schematic of proposed microwave ablation applicator, within a plastic endoscopic cap, for the treatment of esophageal varices

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Fig. 2

Frequency study: comparison of temperature profiles in tissue after 60 W, 40 s heating with monopole antennas tuned to (a) 915 MHz, (b) 2.45 GHz, and (c) 5.8 GHz. Solid black lines highlight the areas of temperature higher than 45 °C (outer black line) and 55 °C (inner black line). (d) Radial temperature profiles for each frequency.

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Fig. 3

Sagittal view of the radiating tip of (a) original directional microwave ablation applicator and (b) modified applicator for ablation of esophageal varices

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Fig. 4

Temperature profiles after 60 W, 40 s ablation using directional microwave applicators with (a) straight linear monopole element, (b) monopole bent by 5 deg, and (c) monopole bent by 7 deg

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Fig. 5

Geometry of simulation for evaluating influence of the endoscopic cap

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Fig. 6

Simulated electric field profiles for (a) microwave applicator within an endoscopic cap and (b) without the endoscopic cap. Simulated temperature profile after 60 W, 50 s ablation (c) with an endoscopic cap and (d) without an endoscopic cap.

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Fig. 7

(a) Illustration of ex vivo experimental setup and parameterization for characterizing ablation zone dimensions. Parameter “r” stands for radial ablation extent and “h” for overall height of ablation. (b) Setup for ex vivo vessel sealing experiments.

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Fig. 8

Sample result of ex vivo experiment: (a) radial ablation extent r, (b) axial ablation extent h, and (c) mucosa layer after experiment

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Fig. 9

Photograph of equine vein (a) before and (b) after 20 s ablation (location marked by a circle)

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Fig. 10

Photograph of the porcine splenic vein suctioned into the cap fixture during in vivo experiment

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Fig. 11

Histopathology images of porcine vein sections: (a) intact and (b) and (c) thermally sealed

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