Bio-Medical RF Simulations with CST Microwave Studio Biological Models Specific Absorption Rate (SAR) Bio-Medical Examples
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
Homogeneous Hand/Body Models New.obj import allows import of biological models, e.g. from Poser 8 (http://my.smithmicro.com/win/poser/index.html) For most high frequency applications fully sufficient Simulate much faster then voxel models
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!! www.sam-phantom.com
CTIA Hand Models Hand fold Hand narrowdata Hand monoblock Hand PDA
CST Voxel Family CHILD BABY KATJA (pregnant) LAURA DONNA EMMA GUSTAV
CST Voxel Family Macros -> Solver -> Calculate Human Material Properties
HUGO Available in different resolutions Materials of interest can be chosen Visible Human Project produced by the National Library of Medicine (NLM), Maryland http://www.vr-laboratory.com/
Cole-Cole-Materials
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
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 1528.1, 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)
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 1528.1 requirements for hexahedral time domain codes (end of 2010) 1528.2 application to cars with passenger/bystander (~2011) 1528.3 application to mobile phones near head (~2011) 1528.4 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.
Visualization of SAR 2D or 3D plot including information about position of the maximum
Visualization of Max. SAR Cube
Dispersive Broadband Simulation Typical requirement for dual band phones: Re(e r ) Im(e r ) 0.9 GHz 41.5 17.98 (= 0.9 S/m) 1.8 GHz 40.0 13.98 (= 1.4 S/m) Frequency dependent material definition: Second order dispersive fit for tabulated values, only one simulation run required
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 1.35 1.31 1.74 0.9 GHz, 10g 0.96 0.93 1.13 Dispersive fit agrees very well for S-Parameter and SAR values in both bands for only 25% extra simulation time 1.8 GHz, 1g 0.69 1.32 1.32 1.8 GHz, 10g 0.99 0.83 0.83
Measured vs. Computed SAR Distribution Example: 7T MRI endorectal coil 0 db = 2.8 W/kg Overall: SAR computed SAR measured 1.08 1.15 Measurement Simulation Courtesy of Erwin L. Hahn Institute Essen,Germany
Magnetic Resonance Imaging (MRI) Three EM-fields needed for imaging STRONG magnetostatic field (human: 1 9.4 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 (60 500 MHz) Rotating B-Field most interesting (B1+) -> Both T- and F-Solvers are of intererst! Most interesting for MRI R&D
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
8 Channel Head Coil Courtesy of Erwin L. Hahn Institute Essen,Germany
8 Channel Head Coil Vs/m² B 1+ SAR voxel arg(b 1+ ) [ ] SAR 10g
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
Spine Loop Array loops overlapped and shifted 70 cm cable length box with TR-switches + pre-amps 20 cm x z 43 cm
Comparison to Measurement Measurement max B 1+ = 15.9 µt Simulation max B 1+ = 13.5 µt
SAR Compliance critical aspect: localized SAR (10g averaged)
Microwave Breast Cancer detection Dr. Maciej Klemm, Electromagnetics Group, Centre for Communications Research (CCR), University of Bristol, United Kingdom e-mail: m.klemm@bristol.ac.uk
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)
Pace Maker Simulation Complete Technology: T-Solver T-Solver F-Solver
Results at 400 MHz Inside biological tissue phantom SAR E-Field Averaging Cube for max SAR
Pacemaker inside Human Body Model
Cardiac Pace Maker Frequency dependent field coupling into a Cardiac Pace Maker (CPM) Courtesy of Lehrstuhl für Theoretische Elektrotechnik, Bergische Universität Wuppertal, Germany
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
New CST Examples! Can only be opened by customers who have -Voxel Import - BioModel License -> offer for evaluation license!!
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
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