Finite Element Modeling of Hepatic Radiofrequency Ablation

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Finite Element Modeling of Hepatic Radiofrequency
Ablation

• Andrew S. Wright MD
• University of Wisconsin
• 5/2/02

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Background

• Surgical resection is the gold standard for
  treatment of hepatic tumors
• Hepatic radiofrequency ablation increases the
  number of patients eligible for curative therapy
• Heating of tissue with RF energy
• Coagulation Necrosis
• Cell Death
• Local recurrence 2-50

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Bioengineering Approach

• Define Problem
• Develop Model System
• Determine Possible Solutions
• Model and Test
• Refine

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Define Problem

• Heating due primarily to thermal conduction
• Poor performance near vessels
• Uneven or irregular heating

Several mms
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Define Problem

• Heating due primarily to thermal conduction
• Poor performance near vessels
• Uneven or irregular heating
• Difficult to treat large or multiple tumors

Images from Dodd et al. AJR 2001
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Finite Element Modeling

• Bioheat Equation

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Finite Element Modeling

• Bioheat Equation
• Lesion ? (Energy Applied x Local Tissue Factors)
  Energy Lost

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Finite Element Modeling
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Finite Element Modeling
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Determine Possible Solutions

• Improve Probe Design
• Bipolar Array

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Determine Possible Solutions

• Improve Probe Design
• Bipolar Array

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Determine Possible Solutions

• Improve Probe Design
• Bipolar Array

Monopolar Bipolar
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Determine Possible Solutions

• Improve Probe Design
• Bipolar Array
• Multiple Probe RF Ablation
• Synergy of simultaneous overlapping ablations

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Multiple Probe RF Ablation
Temperature
Current Density
Simultaneous Activation at 3 probes
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Multiple Probe RF Ablation
Temperature
Current Density
Rapid Switching between 3 probes
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Multiple Probe RF Ablation
Conventional
Switched


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Determine Possible Solutions

• Improve Probe Design
• Bipolar Array
• Multiple Probe RF Ablation
• Synergy of simultaneous overlapping ablations
• Exploit Difference in Physical Properties of
  Tumor and Normal Liver
• Alter frequency of RF energy

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Tumor Resistivity

• Electrical properties of normal liver and tumor
  (K12/TRb) measured in an in vivo rat liver model

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Tumor Resistivity

• Finite Element Model

Tumor diameter 2 cm
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Tumor Resistivity

• Current Density

500 kHz
100Hz
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Tumor Resistivity

• Temperature

500 kHz
100Hz
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Tumor Resistivity

• Lesion Difference

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Tumor Resistivity

• Human
• Colorectal metastasis to liver

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Future Directions

• Further development and clinical testing
• Multiple Probe RF
• Variable-frequency RF
• Microwave Ablation
• Elastography and Thermal Monitoring

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Future Directions

• Modify local tissue factors
• Tumor-specific ablation sensitizers
• Adjuvant or neo-adjuvant chemotherapy
• Alternative Technologies
• Biomolecular Engineering
• Non-invasive Confocal Microwave Ablation

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Acknowledgements

• David Mahvi MD
• Fred Lee Jr. MD
• John Webster PhD
• Dieter Haemmerich PhD
• Tyler Staelin MD