MRI Induced Heating of a Pacemaker. Peter Krenz, Application Engineer

Transcription

1 MRI Induced Heating of a Pacemaker Peter Krenz, Application Engineer 1

2 Problem Statement Electric fields generated during MRI exposure are dissipated in tissue of the human body resulting in a temperature rise Multi-physics simulation can predict this temperature increase ANSYS Workbench workflow allows the user to predefine simulation setups that enable non-experts to successfully execute this multi-physics simulation 2

3 What Tools are Required? Electromagnetic power dissipated in the human body positioned inside an MRI coil: ANSYS HFSS Temperature rise in the human body due to dissipation of electromagnetic power: ANSYS Mechanical System level tool that enables HFSS and Mechanical to interact and exchange simulation results: ANSYS Workbench 3

4 What is HFSS? Premier 3D Electromagnetic design tool Solves Any arbitrary 3D structure Uses Full Wave Finite Element Method (FEM) Transient Finite Element Solver Integral Equation Solver Physical Optics Solver 4

5 What is ANSYS Mechanical? Comprehensive product solution for structural analysis Analysis types available in ANSYS Mechanical: Structural (static and transient): Linear and nonlinear structural analyses Dynamics: Modal, harmonic, random vibration, flexible and rigid dynamics Heat Transfer (steady state and transient): Solve for temperature field and heat flux Temperature-dependent conductivity, convection, radiation and materials allowed 5

6 What is ANSYS Workbench ANSYS Workbench is a project-management tool that is the top-level interface linking all ANSYS software Handles the passing of data between ANSYS Geometry / Mesh / Solver / Post-processing tools Manages project and individual files on disk (geometry, mesh etc.) and provides graphical project details making it easy for the user to understand how a project has been built Because Workbench manages the individual applications AND passes data between them, it is easy to automatically perform design studies (parametric analyses) for design optimization 6

7 ANSYS Workbench Connections between cells indicate sharing of information: Geometry Simulation results from one simulation serve as a setup (input) condition for a second simulation 7

8 ANSYS Workbench The Archive tool can be used to bundle the many files and directories of the Workbench project to send the simulation to colleagues for further setup/analysis This enables leveraging of people in the organization with different strengths and disciplines 8

9 MRI Induced Implant Heating Simulation using ANSYS Workbench + = HFSS Simulation Transient Thermal Simulation Temperature Profile 9

10 Workflow 10

11 Workflow Overview 11

12 Geometry Definition The human body model and pacemaker are defined in a HFSS cell The built-in 3D modeler was used for geometry creation and manipulation (note this is not a simulation) External CAD programs can be used for object creation and directly linked into workflow 12

13 Human Body Model The human body model contains three levels of defeaturing to accommodate varying degrees of accuracy Material properties that are included: Frequency dependent values for electro-magnetic simulations Constant values for thermal simulations A user can include as much detail of the body model as required in an MRI induced heating simulation 13

14 Pacemaker A pacemaker was created and positioned within the human body model using the HFSS 3D modeler 14

15 HFSS Simulation MR coil and simulation setup is pre-defined: Geometry Boundary conditions Excitation Simulation setup No user input is required MRI coils operating at 64 and 128 MHz are available Due to pre-defined HFSS simulation setup, non-expert HFSS users are able to successfully execute this simulation 15

16 HFSS Simulation Geometry of human body model with pacemaker are inserted into pre-defined HFSS simulation containing MRI coil Ready to simulate + = 16

17 Meshing HFSS creates and refines mesh automatically No user-input required Geometry Initial Mesh Final Mesh 17

18 HFSS Simulation Results HFSS simulation results can be visualized: Electric field distribution SAR distribution 18

19 Thermal Simulation Geometry of human body and pacemaker are passed from HFSS to ANSYS Mechanical Electric fields dissipated in human tissue or on surfaces of metal conductors are the source of the temperature rise calculated by ANSYS Mechanical 19

20 Thermal Simulation Only keep what is required: Do not include MRI coil in thermal simulation, since it does not impact temperature distribution in human body Do not include organs and bones located away from pacemaker, since they will not influence the temperature distribution near the implant 20

21 Analysis Setup Define analysis setup to replicate measurement conditions Specify duration of how long MRI is turned on and off MR Coil: On Off 21

22 Meshing Meshing in ANSYS Mechanical works best on smaller volumes Human body was split into several sub-sections to facilitate meshing 22

23 Temperature Profile Different ways to visualize the temperature rise in the entire human body: Temperature rise on surface of human body after 15 minutes of exposure to MRI is shown on left Maximum temperature rise in entire human body as a function of time is shown below 23

24 Temperature Profile Temperature profile on individual components can be visualized Pacemaker is shown here 24

25 Final Thoughts MRI heating of human body with pacemaker was simulated using ANSYS Workbench linking HFSS and Mechanical Simulation replicates physical structure of MRI coil and human body to ensure accurate results Workflow is a simulation template: Simulation setups are pre-defined to enable non-experts to execute simulation successfully Workflow allows sharing and collaborating on simulation leverage strengths of people on your team 25

26 Thank you! Questions? 26