07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference ›...
Transcript of 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference ›...
![Page 1: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/1.jpg)
© 2011 ANSYS, Inc. October 24, 20111
MRI Device Compliance
Martin Vogel, PhDKimberley PolingApplication Engineering Team Eastern USA
![Page 2: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/2.jpg)
© 2011 ANSYS, Inc. October 24, 20112
Overview
High simulation efficiency for MRI
Method that enables a non‐EE to analyze the thermal effects of an MRI scan on an implant
![Page 3: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/3.jpg)
© 2011 ANSYS, Inc. October 24, 20113
Main tools
HFSS – 3D Full‐wave Electromagnetic simulator
Designer– Circuit simulator that interacts with HFSS
ANSYS Professional NLT– Thermal simulator that uses electromagnetic losses from HFSS as heat loads
![Page 4: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/4.jpg)
© 2011 ANSYS, Inc. October 24, 20114
1. Simulation efficiency
Minimize RAM and simulation time
![Page 5: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/5.jpg)
© 2011 ANSYS, Inc. October 24, 20115
Generic birdcage coil
Ring with 24 ports, phases 0 – 345 deg
Ring with 24 ports,phases -180 – 165 deg
Around the coil is acylindrical shield withopen ends.
![Page 6: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/6.jpg)
© 2011 ANSYS, Inc. October 24, 20116
Saving computer resources
A birdcage coil can be created with many, e.g. 48, sources that impose the required rotating field.
A realistic birdcage coil has few sources and many capacitors.
Such a coil can be simulated with less resources.
With a couple of ANSYS tools, we have created such realistic coils, one for 1.5 T and one for 3 T.
![Page 7: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/7.jpg)
© 2011 ANSYS, Inc. October 24, 20117
Realistic coil feed network
0
0
0
0
0
0
0
0
RZ=50ohmIZ=0ohm
PNUM=1
IZ=0ohm
PNUM=2RZ=50ohm
IZ=0ohm
PNUM=3RZ=50ohm
RZ=50ohm
IZ=0ohm
PNUM=4
Bot_1:1Bot_2:1
Bot_3:1Bot_4:1Bot_5:1
Bot_6:1Bot_7:1Bot_8:1
Bot_9:1Bot_10:1Bot_11:1
Bot_12:1Bot_13:1Bot_14:1
Bot_15:1Bot_16:1Bot_17:1Bot_18:1
Bot_19:1Bot_20:1Bot_21:1
Bot_22:1Bot_23:1Bot_24:1
Top_1:1Top_2:1
Top_3:1Top_4:1Top_5:1
Top_6:1Top_7:1Top_8:1
Top_9:1Top_10:1Top_11:1
Top_12:1Top_13:1Top_14:1
Top_15:1Top_16:1Top_17:1Top_18:1
Top_19:1Top_20:1Top_21:1
Top_22:1Top_23:1Top_24:1
Cap
C4
Cap
C5
Cap
C6
Cap
C7
Cap
C8
Cap
C16Cap
C17Cap
C18Cap
C19Cap
C20
Cap
C23Cap
C24Cap
C25Cap
C26
Cap
C34Cap
C35Cap
C36Cap
C37Cap
C38Cap
C39
Cap
C40Cap
C41Cap
C42Cap
C43Cap
C44
Cap
C53Cap
C54Cap
C55Cap
C56Cap
C57
Cap
C59Cap
C60Cap
C61Cap
C62Cap
C63Cap
C64
Cap
C65Cap
C66Cap
C67Cap
C68Cap
C69Cap
C70
Cap
C237
Cap
C240
Feed points are driven with phases 0, 90, 180 and 270 degrees.
Feed points simplified and optimized with ports and capacitors
![Page 8: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/8.jpg)
© 2011 ANSYS, Inc. October 24, 20118
S11 coils with capacitors
63.8 MHz
127.6 MHz
![Page 9: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/9.jpg)
© 2011 ANSYS, Inc. October 24, 20119
Fine‐tune capacitors for MRI image quality
1.5 T124.5 pF
3 T26.5 pF
B+/B‐ ratio is at least 20
![Page 10: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/10.jpg)
© 2011 ANSYS, Inc. October 24, 201110
Rotating H with capacitors
Feed points
Capacitors have been fine-tuned in HFSS for best rotating H after optimization in Designer.
![Page 11: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/11.jpg)
© 2011 ANSYS, Inc. October 24, 201111
Apply this design technique to birdcage coil with human‐body model
RAM 12.5 GB
Elapsed time 58 minutes
![Page 12: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/12.jpg)
© 2011 ANSYS, Inc. October 24, 201112
Rotating B for body in birdcage with 48 sources Compare with results of other simulations.
![Page 13: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/13.jpg)
© 2011 ANSYS, Inc. October 24, 201113
Rotating B for homogeneous body in birdcage with 4 sources and 44 capacitors is quite similar.
RAM 5.5 GB
Elapsed time 22 minutes
![Page 14: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/14.jpg)
© 2011 ANSYS, Inc. October 24, 201114
Is it possible to simulate just the blue volume and IMPOSE fields from a separate coil simulation? YES, you can do that!
![Page 15: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/15.jpg)
© 2011 ANSYS, Inc. October 24, 201115
With imposed fields, the rotating B again looks very similar!
RAM 1.6 GB
Elapsed time 7.3 minutes
![Page 16: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/16.jpg)
© 2011 ANSYS, Inc. October 24, 201116
Now that we have such an efficient method, use it with a complicated heterogeneous human‐body model and a pacemaker.
RAM 4.3 GB
Elapsed time 20 minutes
![Page 17: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/17.jpg)
© 2011 ANSYS, Inc. October 24, 201117
Now that we have such an efficient method, use it with a complicated heterogeneous human‐body model and a pacemaker.
RAM 4.3 GB
Elapsed time 20 minutes
![Page 18: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/18.jpg)
© 2011 ANSYS, Inc. October 24, 201118
Local SAR in cut plane (3T coil)
![Page 19: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/19.jpg)
© 2011 ANSYS, Inc. October 24, 201119
R13 Schematic
![Page 20: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/20.jpg)
© 2011 ANSYS, Inc. October 24, 201120
Thermal resultMaximum occurs on neck, not at implant
![Page 21: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/21.jpg)
© 2011 ANSYS, Inc. October 24, 201121
Contours of 38.1 0C and higher
Tissue around pacemaker
![Page 22: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/22.jpg)
© 2011 ANSYS, Inc. October 24, 201122
Pacemaker, lead and heart
![Page 23: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/23.jpg)
© 2011 ANSYS, Inc. October 24, 201123
2. Thermal effects of MRI scan on implant
Minimize the implant designer’s exposure to electromagnetics
![Page 24: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/24.jpg)
© 2011 ANSYS, Inc. October 24, 201124
Generic birdcage coil
Around the coil is acylindrical shield withopen ends.
![Page 25: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/25.jpg)
© 2011 ANSYS, Inc. October 24, 201125
Where should implants be placed?
Implants should have worst‐case location and orientation.
Next few slides illustrate how this is achieved.
![Page 26: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/26.jpg)
© 2011 ANSYS, Inc. October 24, 201126
Phantom placement
|B| is almost uniform within coil (left). However, |E| is not (right).Make sure implants be located in a region with relative high E-field.
|B|
|E|
![Page 27: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/27.jpg)
© 2011 ANSYS, Inc. October 24, 201127
Worst‐case SAR: implant near phantom wall; does not stick out of RF coil
![Page 28: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/28.jpg)
© 2011 ANSYS, Inc. October 24, 201128
Worst case: implant parallel with electric‐field vectors
![Page 29: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/29.jpg)
© 2011 ANSYS, Inc. October 24, 201129
Workflow for implant testing
Have reusable coil+phantom model in HFSS
Have phantom+parameterized implant(s) in separate geometry system
This separate geometry will be exposed to the fields from the coils.
Thermal simulator will determine temperatures of phantom+implant(s) due to RF losses.
Next slides show this in more detail.
![Page 30: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/30.jpg)
© 2011 ANSYS, Inc. October 24, 201130
Workflow in R14 Schematic
CAD
No need to open HFSS.
![Page 31: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/31.jpg)
© 2011 ANSYS, Inc. October 24, 201131
Create in other CAD tool import with parameters into prepared HFSS design
![Page 32: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/32.jpg)
© 2011 ANSYS, Inc. October 24, 201132
Transfer geometry to thermal simulatorNo more need for File/Export and File/Import
Note the parameters from The CAD tool are available!
![Page 33: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/33.jpg)
© 2011 ANSYS, Inc. October 24, 201133
Library of thermal material properties is available
![Page 34: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/34.jpg)
© 2011 ANSYS, Inc. October 24, 201134
Have prepared a subset with the same material names as in HFSS.
![Page 35: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/35.jpg)
© 2011 ANSYS, Inc. October 24, 201135
Objects come in with correct material assignment!
![Page 36: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/36.jpg)
© 2011 ANSYS, Inc. October 24, 201136
Drag and Drop HFSS Solution to Thermal Setup
Drop and Drag
Resulting Schematic with extra Link
![Page 37: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/37.jpg)
© 2011 ANSYS, Inc. October 24, 201137
Assign Losses from HFSS to Objects in Thermal
![Page 38: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/38.jpg)
© 2011 ANSYS, Inc. October 24, 201138
Effect implants on local SAR
![Page 39: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/39.jpg)
© 2011 ANSYS, Inc. October 24, 201139
Temperatures on implants after 900 s
![Page 40: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/40.jpg)
© 2011 ANSYS, Inc. October 24, 201140
Add final maximum temperature as an output parameter
![Page 41: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/41.jpg)
© 2011 ANSYS, Inc. October 24, 201141
Input parameter:Implant length
Output parameter:Max. temperature
![Page 42: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/42.jpg)
© 2011 ANSYS, Inc. October 24, 201142
Attach DX to investigate design variations efficiently
Vary length and inspect final temperatures
![Page 43: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/43.jpg)
© 2011 ANSYS, Inc. October 24, 201143
Maximum temperature as a function of implant length (at reduced power, not to be compared with previous result)
40 60 80 100 120 140 160 180 Length implant (mm)
![Page 44: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/44.jpg)
© 2011 ANSYS, Inc. October 24, 201144
Observations
Temperatures tend to decrease when implant is buried deeper.This makes sense, as electromagnetic fields decay with depth.
For small implants, temperatures increase with implant length.This makes sense, because a longer implant can function as a more effective receiving antenna (as long as implant ≤ λ/2 at this frequency and in this environment).
For large implants, field inhomogeneity makes predictions harder to make.
Results are sensitive to the gel’s electrical and thermal material properties.
![Page 45: 07 MRI device compliance - support.ansys.com › staticassets › ANSYS › Conference › Minn… · A birdcage coil can be created with many, e.g. 48, sources that impose the required](https://reader034.fdocuments.in/reader034/viewer/2022052500/5f1cd4f4e989f414fb06d4be/html5/thumbnails/45.jpg)
© 2011 ANSYS, Inc. October 24, 201145
Summary
We have demonstrated
(1) A way to achieve very efficient simulations;(2) A simulation flow that enables non‐EM experts to determine MRI‐induced heating for different implant designs.