pacificon talk
TRANSCRIPT
Antennas in Magnetic Resonance Imaging
John M. PaulyAG6WH
Stanford University
http://www.stanford.edu/~pauly
Why MRI?
K. Pauly, G. Gold Stanford Rad 220
MRI Contrast
Angiography Musculo-skeletalK. Pauly, G. Gold
Stanford Rad 220
MRI Applications
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•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
How Does MRI Work?
µ
Magnetic Moment
1H Atom
µ
µ
µ
µ
µ
µ
µ
µ
µ
µ
B0
M0
Polarization
No Polarization Polarized
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
MRI Scanner
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
K. Pauly, G. GoldStanford Rad 220
Spectrum
TimeSignal
Piano Analogy
Body
ReceiveSignal
ω(x) = γGx
s(t)
S(ω)
ω
ReceiveSpectrum
Spatial Encoding
Transmit Antennas
MRI Scanner
Transmit Coil
Hayes, et al. JMR 1985
Schematic Field Pattern Experiment
Birdcage Modes
One Drive Port : Linear Polarization
RF
Bei Zhang, ISMRM 2016
Birdcage Coil
Two Drive Ports : Circular Polarization
RFIRFQ
Rotation
Birdcage Modes
Bei Zhang, ISMRM 2016
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
Parallel Transmit B1 ShimmingRF Linearization
Pascal Stang, Greig Scott, Stanford
4ch Tx Coil with sensors
Coil current sensor
Secondary Winding on Inner Layers
Primary Winding on
Outer Layers
(a)
RF Current Sensor
Linearize Entire Transmit Chain
Receive Antennas
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Receive Coils
Zhang et al, MRM 2015
Array Receive Coils
Coil layout
Receive Coils
Zhang et al, MRM 2015Array Receive Coils
Circuit for an Individual Element
Receive Coils
Zhang et al, MRM 2015Array Receive Coils
Individual Coil Sensitivities
Image courtesy: Siemens
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Current Receive Coils
Cables and Baluns Constraining Arrays
Wearable Wireless Coil Arrays
Software Defined Multi-Channel
Receiver
Wireless PowerPilot Tone
Q-spoilClock
In-Bore propagationLow Power Digital
Transponders
Wearable Wireless Coil Arrays
Wireless Power
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“Tesla apparatus”, Secor, 1921
Near-Field Power
Batteriescouldlimitscantime
Needabout100mWperchannel
Ourgoalistodeliver10W
MinimalinteractioninsidetheMRIbore
Wireless Power For Array Coils
K. Byron, et al. ISMRM 2016, Stanford
Wireless Power Transfer System
DiodeRectifierPickup
Coil
PrimaryCoil
10MHzλ/4FilterAntennaTunerPowerAmplifier
StorageCapacitor
Filter
RFSwitch
50Ω
Signal source
64MHzλ/4
Controlledby:1) Medusa
module2) Triggerdelayed
fromtheTXexciterunblanksignal
RF Gated System
Drivepoweriscycledonandoff
at1Hz
Wireless Powering 11W Light
NotTransmitting0.0215rms
Harvesting1WRFGated0.0221rms
Harvestingestimated5WRFGated0.0219rms
Areausedtomeasurebackgroundnoisevoltage
Noise Measurements
Low Power Electronics
Possible Design: Swaddle Coil
Transponders handleseveral local coils
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
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
Synchronization
LNA A/D
IF
MRI requires great frequency stability
Where do we get the IF signal?
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
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
Synchronization
LNA A/D
IFUse a local oscillator forthe IF
Transmit it out, and trackits frequency
Fix the data up later
~LO
Synchronization
LNA A/D
IF
Track the transmit RF
Very frequency stable
Very high SNR
Problem: people do strangethings with RF waveformsTransmit RF Coil
Wireless Data
RF coils
Low Power, mm-Wave Transmitter
mm-Wave Receiver
Wireless Data Transmission
Image: IEEE SpectrumKamal Aggarwal, Ada Poon
Stanford
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
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
60 GHz Radio
Aggarwal, Taghivand, Rajavi, and Poon, Stanford
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
FR4 PCB
On-chip Dipole
Thinned to 100µm from 600µm
Max gain: 1.6dBi
On Chip Antenna Gain
Metal Reflector at lambda/4
FR4 PCB
λ/4 On-chip Dipole Thinned to 100µm
Max gain: 5.2dBi
Add Metal Reflector
Metal Reflector
FR4 Dielectric lens
FR4 PCB
λ/2
λ/4 On-chip Dipole Thinned to 100µm
Max gain: 9.1dBi
Add Dielectic Lens
Flexible Coils Printed on Fabric
Printed Electronics
J. Corea, B. Lechene, A. Flynn, A.C. Arias, M. Lustig UCB
Printed Electronics
Flexible Receive Array
Two Four-Channel Printed CoilsEight channel printed coil array (left)
Twelve Channel Commercial Array Coil (right)
Receive Array Performance
Eight Channel Printed Coil
Twelve Channel CommercialArray Coil
4-Channel Neonate Coil
Four Channel NeonateSwaddle Coil
4D Flow Images5X acceleration
Conclusions
Conclusions
LotsofantennasinanMRIsystem
LotsofborrowedHamRadiotechnology
•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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Wireless Future1921