Bio-Medical RF Simulations with CST Microwave Studio

Transcription

1 Bio-Medical RF Simulations with CST Microwave Studio Biological Models Specific Absorption Rate (SAR) Bio-Medical Examples

2 Biological Models The right choice of the biological model is essential for the reliability of a SAR or EMI simulation. CST Voxel Family Visible Human voxel data SAM Phantom, homogeneous models other voxel data

3 Homogeneous Hand/Body Models New.obj import allows import of biological models, e.g. from Poser 8 ( For most high frequency applications fully sufficient Simulate much faster then voxel models

4 SAM - Standard Anthropomorphic Model Originally created for measurements Shape specified in IEEE/CENELEC/IEC standards Filled with homogeneous glycol-containing tissue-simulant liquid, only two materials for simulation Virtual prototyping through simulation plastic shell tissue simulant liquid (TSL) Frequency dependent material properties (according to standard) can be modelled by dispersive materials via tabulated input. Only one simulation run for broadband results!!

5 CTIA Hand Models Hand fold Hand narrowdata Hand monoblock Hand PDA

6 CST Voxel Family CHILD BABY KATJA (pregnant) LAURA DONNA EMMA GUSTAV

7 CST Voxel Family Macros -> Solver -> Calculate Human Material Properties

8 HUGO Available in different resolutions Materials of interest can be chosen Visible Human Project produced by the National Library of Medicine (NLM), Maryland

9 Cole-Cole-Materials

10 SAR: Overview and Background SAR Specific Absorbtion Rate A measure for electromagnetic energy absorbed by biological tissue mass when exposed to radiating device (e.g. mobile phone) 2 2 P E J SAR 2 2 Typically averaged over pre-defined mass Unit of SAR: W/kg P: Power loss density E: Electric field strength J: Current density s: Conductivity r: Density

11 Averaging Procedure 1. Point of avg. SAR calculation 2. Search for 10 g cube (iteratively) 3. Integrate losses in cube At boundary treatment depends on chosen averaging standard: IEEE C95.3, IEEE , CST C95.3 CST legacy The constant volume assumption uses an averaged cube size: - Faster (no iterative search for cube with correct mass) - Only approximative (not according to official SAR standard)

12 SAR Standards under Development Several guidelines and standards specify SAR safety limits (i.e. ICNIRP). Standards like IEEE 1528 regulate measurement methods for practical assessment of compliance. A simulation standard IEEE 1528.X is in development requirements for hexahedral time domain codes (end of 2010) application to cars with passenger/bystander (~2011) application to mobile phones near head (~2011) requirements for tetrahedral frequency domain codes CST participates in standards committee. IEEE C95.3 Annex E specifies SAR averaging scheme for simulation. CST MICROWAVE STUDIO has already been approved by the FCC (USA) to comply with hex td standard drafts.

13 Visualization of SAR 2D or 3D plot including information about position of the maximum

14 Visualization of Max. SAR Cube

15 Dispersive Broadband Simulation Typical requirement for dual band phones: Re(e r ) Im(e r ) 0.9 GHz (= 0.9 S/m) 1.8 GHz (= 1.4 S/m) Frequency dependent material definition: Second order dispersive fit for tabulated values, only one simulation run required

16 Dispersive Broadband Simulation S-Parameter comparison: Compared material settings: Constant settings for 0.9 GHz sim. time 45 min. Constant settings for 1.8 GHz sim. time 45 min. Dispersive broadband fit total sim. time: 57 min. SAR value comparison: 0.9 GHz, 1g GHz, 10g Dispersive fit agrees very well for S-Parameter and SAR values in both bands for only 25% extra simulation time 1.8 GHz, 1g GHz, 10g

17 Measured vs. Computed SAR Distribution Example: 7T MRI endorectal coil 0 db = 2.8 W/kg Overall: SAR computed SAR measured Measurement Simulation Courtesy of Erwin L. Hahn Institute Essen,Germany

18 Magnetic Resonance Imaging (MRI) Three EM-fields needed for imaging STRONG magnetostatic field (human: Tesla, up to 21 T for animals) Mostly superconducting magnets, aligning the spinning protons -> M-Statik Solver Gradient field for positioning (in khz range) -> Magneto-Quasistatik Solver, LT-Solver HF field to excite spinning protons and receive relaxation signal ( MHz) Rotating B-Field most interesting (B1+) -> Both T- and F-Solvers are of intererst! Most interesting for MRI R&D

19 Design Challenge: Increase SNR of image SNR ~ static biasing field ~ spin resonance frequency f res For 7T MRI -> f res = 297 MHz -> l body ~ 13 cm -> It is difficult to obtain homogeneous field distribution inside body, specialized coils required Safety issue: SAR ~ f res 2 -> SAR critical for higher f res -> Alternative: queck directly body temperature increase, bioheat solver! Advantages of CST: Complete Technology, Static, LF, T, F and bioheat solvers in one frontend, Voxel Family, fast SAR, etc

20 8 Channel Head Coil Courtesy of Erwin L. Hahn Institute Essen,Germany

21 8 Channel Head Coil Vs/m² B 1+ SAR voxel arg(b 1+ ) [ ] SAR 10g

22 8 Channel Head Coil location of max. SAR 10g in left shoulder for off-centre position of head max. perm. power = 23 W (CW) location of max. SAR on left side of the head SAR 10g most critical aspect SAR 10g SAR head 25 W max. perm. power 27 W 33 W SAR 10g

23 Spine Loop Array loops overlapped and shifted 70 cm cable length box with TR-switches + pre-amps 20 cm x z 43 cm

24 Comparison to Measurement Measurement max B 1+ = 15.9 µt Simulation max B 1+ = 13.5 µt

25 SAR Compliance critical aspect: localized SAR (10g averaged)

26 Microwave Breast Cancer detection Dr. Maciej Klemm, Electromagnetics Group, Centre for Communications Research (CCR), University of Bristol, United Kingdom

27 Model setup and clinical results dipole antennas dispersive tissues inhomogeneous breast! model 30-40M cells full imaging (30 simulations) takes about 10h (hardware accelerated; 4 GPU cards)

28 Pace Maker Simulation Complete Technology: T-Solver T-Solver F-Solver

29 Results at 400 MHz Inside biological tissue phantom SAR E-Field Averaging Cube for max SAR

30 Pacemaker inside Human Body Model

31 Cardiac Pace Maker Frequency dependent field coupling into a Cardiac Pace Maker (CPM) Courtesy of Lehrstuhl für Theoretische Elektrotechnik, Bergische Universität Wuppertal, Germany

32 BABY besides Baby-Phone Stimulated power: 500 mw at 865 MHz Max. SAR value (averaged over 10g): 0.02 W/kg (well below accepted maximum of 2 W/kg for public exposure) Courtesy of Lehrstuhl für Theoretische Elektrotechnik, Bergische Universität Wuppertal, Germany

33 New CST Examples! Can only be opened by customers who have -Voxel Import - BioModel License -> offer for evaluation license!!

34 Summary CST STUDIO SUITE offers a wide range of tools for bio-medical simulations (MRI, cancer treatment, diathermy, implants, etc.) Both flexible homogeneous and detailed voxel models are available Complete Technology allows combined simulations from static to GHz including circuit simulation SAR and Bio-Thermal simulations help to improve performance and safety of medical devices

35 Appendix