Download - Pacificon Talk
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Antennas in Magnetic Resonance Imaging
John M. PaulyAG6WH
Stanford University
http://www.stanford.edu/~pauly
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Why MRI?
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K. Pauly, G. Gold Stanford Rad 220
MRI Contrast
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Angiography Musculo-skeletalK. Pauly, G. Gold
Stanford Rad 220
MRI Applications
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5
•Coronary Artery•3T Scanner•10 Images/s
Real Time MRI
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Reed Busse, PhD, GE ASL West
35 week old fetus with nodularity along ventricles and failure of development of the corpus callosum
Reed Busse, PhD, GE ASL West
Fetal MRI
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How Does MRI Work?
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µ
Magnetic Moment
1H Atom
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µ
µ
µ
µ
µ
µ
µ
µ
µ
µ
B0
M0
Polarization
No Polarization Polarized
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MRI ScannerFigure3:Left)MEDUSAgradientandRFcontrollersystem.Right)EquipmentrackcontainingaMEDUSAsystemtogetherwithRFvectormodulatorsandRFamplifierssupporting8-channelparallelRFtransmit.
Figure4:ProposedInstrument:GEDiscoveryMR7503T,awhole-bodyMRIsystem.
Inadditiontotheimprovementsofferedbytheproposedinstrument,theDepartmentofElectricalEngineer-ing,asdescribedintheattachedletter,iscommitting$200,000forsiteupgradesandinstallationoftheproposedinstrument,includingnewRFshieldingtoallowinstallationofastandardpatienttableandmagnethousing.
Insummary,theMR750isthemostadvanced3TMRIsystemonthemarketandprovidesastate-of-the-artplatformfordevelopment.WeexpecttheinstrumentandsiteupgradestodramaticallyimprovetheresearchcapabilitiesoftheMRSRLsystem,aswellasincreasevolunteercomfortandacceptance,withoutdetractingfromthestrengthsofourpastprograminallowingforsubstantivesystemmodificationandintegrationwithprototypeequipment.SimilarInstrumentsAnumberofother3TMRIsystemsareavailableoncampus,yetnonearesufficientlyavailableorappropriatefortheproposedresearchbeingconductedattheMRSRL.Table1describesthesesystemsaslabeledinthemapshowninFig.5.Locations2and3areimagingcentersthatcontainresearch3TMRIsystemsthatserveawidebodyofdifferentusers.Bothofthesecentersoperatewithsubstantialsupportstaffandchargescanfeesontheorderof$400perhourforcostrecovery.TheMRSRLisauniquefacilityinthe
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MRI Scanner
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Excitation
ω0 = γB0
K. Pauly, G. Gold Stanford Rad 220
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Spatial Encoding
ω(x) = γ(Gx+B0)
K. Pauly, G. Gold Stanford Rad 220
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K. Pauly, G. GoldStanford Rad 220
Spectrum
TimeSignal
Piano Analogy
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Body
ReceiveSignal
ω(x) = γGx
s(t)
S(ω)
ω
ReceiveSpectrum
Spatial Encoding
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Transmit Antennas
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MRI Scanner
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Transmit Coil
Hayes, et al. JMR 1985
Schematic Field Pattern Experiment
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Birdcage Modes
One Drive Port : Linear Polarization
RF
Bei Zhang, ISMRM 2016
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Birdcage Coil
Two Drive Ports : Circular Polarization
RFIRFQ
Rotation
Birdcage Modes
Bei Zhang, ISMRM 2016
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Amp
Amp
Amp
Amp
Amp
RF Source Low powerRF Amps Body Coil
Amp
RF Source High powerRF Amp Body Coil
Parallel Transmit
Single High Power Transmit ChannelMultiple Low Power Transmit Channels
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Parallel Transmit B1 ShimmingRF Linearization
Pascal Stang, Greig Scott, Stanford
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4ch Tx Coil with sensors
Coil current sensor
Secondary Winding on Inner Layers
Primary Winding on
Outer Layers
(a)
RF Current Sensor
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Linearize Entire Transmit Chain
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Receive Antennas
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Receive Coils
Zhang et al, MRM 2015
Array Receive Coils
Coil layout
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Receive Coils
Zhang et al, MRM 2015Array Receive Coils
Circuit for an Individual Element
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Receive Coils
Zhang et al, MRM 2015Array Receive Coils
Individual Coil Sensitivities
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Image courtesy: Siemens
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Current Receive Coils
Cables and Baluns Constraining Arrays
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Wearable Wireless Coil Arrays
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Software Defined Multi-Channel
Receiver
Wireless PowerPilot Tone
Q-spoilClock
In-Bore propagationLow Power Digital
Transponders
Wearable Wireless Coil Arrays
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Wireless Power
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“Tesla apparatus”, Secor, 1921
Near-Field Power
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Batteriescouldlimitscantime
Needabout100mWperchannel
Ourgoalistodeliver10W
MinimalinteractioninsidetheMRIbore
Wireless Power For Array Coils
K. Byron, et al. ISMRM 2016, Stanford
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Wireless Power Transfer System
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DiodeRectifierPickup
Coil
PrimaryCoil
10MHzλ/4FilterAntennaTunerPowerAmplifier
StorageCapacitor
Filter
RFSwitch
50Ω
Signal source
64MHzλ/4
Controlledby:1) Medusa
module2) Triggerdelayed
fromtheTXexciterunblanksignal
RF Gated System
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Drivepoweriscycledonandoff
at1Hz
Wireless Powering 11W Light
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NotTransmitting0.0215rms
Harvesting1WRFGated0.0221rms
Harvestingestimated5WRFGated0.0219rms
Areausedtomeasurebackgroundnoisevoltage
Noise Measurements
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Low Power Electronics
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Possible Design: Swaddle Coil
Transponders handleseveral local coils
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0 50 100 150 200 250.0001
.001
.01
.1
1.0
K Sp
ace
Ampl
itude
500kHz image bandwidth, so 1 Msps or 500 Ksps I/q 16-20bits output, 100 mW/ch.
K-space compressible by ~25% because of significant bit zeros. 50% data acquisition duty cycle.
Leads to 6-8 Mbps per coil with prior decimation, compression, buffering.
MRI Signal Characteristics
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LNA Pipeline 20-80 Msps
Downconvert
decimate20 Mbps transmitter
90-110mW
LNA 18-bit SAR 1Msps
18 Mbps transmitter
10-20mW60-100mW
Poly filter
Low IF image reject
Demodulate to IF
Direct to Digital
Receiver Architectures
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Synchronization
LNA A/D
IF
MRI requires great frequency stability
Where do we get the IF signal?
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Synchronization
LNA A/D
Put a carrier on the 10 MHzwireless power signal
Use a frequency multiplierto get the frequency youwant
Problem: wireless power coilimpedance changes with load
Wireless Power
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Synchronization
LNA A/D
IFTransmit at 1 GHz
Divide down to thefrequency you want
Problem: phase shifts dueto propagation
~ 1 GHz
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Synchronization
1 GHz signal transmittedfrom the magnet bore
Demodulated with theoriginal signal
Variation is due to subject motion
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Synchronization
LNA A/D
IFUse a local oscillator forthe IF
Transmit it out, and trackits frequency
Fix the data up later
~LO
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Synchronization
LNA A/D
IF
Track the transmit RF
Very frequency stable
Very high SNR
Problem: people do strangethings with RF waveformsTransmit RF Coil
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Wireless Data
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RF coils
Low Power, mm-Wave Transmitter
mm-Wave Receiver
Wireless Data Transmission
Image: IEEE SpectrumKamal Aggarwal, Ada Poon
Stanford
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802.11ac
“older” BCM4334 in iPhone 5s
BCM4354, 2x2 MIMO 867 Mb/s in 80 MHz channel (2-stream)
802.11ac (5 GHz)
UWB 3-5GHzPulse-Link Cwave
GEN 1: 1Gb/s
802.11ad 60GHz (WiGig) 4.6 Gb/s SC, 7Gb/s OFDM
Tensorcom < 250mW Wilocity, WIL6300, 200-300mW
WirelessHD (60 GHz)10-28Gb/s
Silicon Image, UltraGig-6400, 500mW
Commercial High Speed Links
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802.11ad 60GHz (WiGig) 4.6 Gb/s SC, 7Gb/s OFDM
Tensorcom < 250mW Wilocity, WIL6300, 200-300mW
WirelessHD (60 GHz)10-28Gb/s
Silicon Image, UltraGig-6400, 500mW
• Power consumption < 15mW
• Distance < 50cm
• Simpler Modulation
• OOK
Commercial High Speed Links
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60 GHz Radio
Aggarwal, Taghivand, Rajavi, and Poon, Stanford
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60 GHz Radio
0.010.1
110
10 100 1000
TX P
ower
(mW
)
Data Rate (Mb/s)
10cm
2 Gb/s at 10 mW
Die Photo Block Diagram -2.7 dBi Antenna Gain
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FR4 PCB
On-chip Dipole
Thinned to 100µm from 600µm
Max gain: 1.6dBi
On Chip Antenna Gain
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Metal Reflector at lambda/4
FR4 PCB
λ/4 On-chip Dipole Thinned to 100µm
Max gain: 5.2dBi
Add Metal Reflector
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Metal Reflector
FR4 Dielectric lens
FR4 PCB
λ/2
λ/4 On-chip Dipole Thinned to 100µm
Max gain: 9.1dBi
Add Dielectic Lens
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Flexible Coils Printed on Fabric
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Printed Electronics
J. Corea, B. Lechene, A. Flynn, A.C. Arias, M. Lustig UCB
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Printed Electronics
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Flexible Receive Array
Two Four-Channel Printed CoilsEight channel printed coil array (left)
Twelve Channel Commercial Array Coil (right)
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Receive Array Performance
Eight Channel Printed Coil
Twelve Channel CommercialArray Coil
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4-Channel Neonate Coil
Four Channel NeonateSwaddle Coil
4D Flow Images5X acceleration
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Conclusions
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Conclusions
LotsofantennasinanMRIsystem
LotsofborrowedHamRadiotechnology
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•MikiLustig,KK6MRI(UCB)
•AnaClaudiaArias(UCB)•JoesphCorea,KK6KKE(UCB)•AnitaFlynn,KI6LO(UCB)•BalthazarLechene(UCB)
•ThomasGrafendorfer(GE)
•FraserRobb(GE)
•GreigScott(Stanford)•PascalStang,KF6PJZ(Stanford)•ShreyasVasanawala(Stanford)•JosephCheng,KK6QYY(Stanford)•JonathanLu,KK6QZH(Stanford)•KellyByron(Stanford)•SawsonTaheri,KG6NUB(Stanford)•KamalAggarwall(Stanford)
•AdaPoon(Stanford)•AndreasPort(ETH) Grant Support: R01EB008108, P41EB015891,
P01CA159992, R01EB009690, R01EB019241, and GE Healthcare
Thanks!
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68
Wireless Future1921