Radio Frequency coil

PresentedbyDarshanKS

Radio Frequency coil •  Radiofrequency coils (RF coils) are the "antenna" of the MRI system,

broadcasting the RF signal to the patient and / or receiving the return signal

•  Types of RF coil •  Volume coil •  Surface coil

•  Frequency formula

f = 1/2𝜋√𝐿𝐶  

d

RF coils

=

d =

d =

d =

d =

d =

d= d=.

d =

d =

d =

d =

d =

d =

d= d=

.Fig1:BiotSavartholdgood,forlowfrequenciesandregionclosetocoil

•  GeneratedmagneCcfield(B-field)canbecalculatedbythelawof‘Biot-Savart’equaCon

•  dB= 𝜇0 /4𝜋   𝐼 𝑑𝑙∗𝑟/|𝑟|^3 

Design Parameters

Design• Volume coil 1.5Tesla(1.5MHz)

Ø Coil radius – 1.6cm Ø Leg length - 2.75cm Ø Leg width – 0.5cm Ø Seg width – 10.05cm Ø Seg length - 1.26cm

•  8 Rung •  fo = 63.8MHz (1.5 Tesla)

Fig:Samplebirdcagecoil

Design •  Surface coil

Ø N=1 Ø  Loop Diameter =2.6cm Ø  Inductance

RF Coils

Fig1:Birdcagecoil

Fig2:Surfaceloop

Fig3:Phasedarraycoil

Fig:Birdcagecoilat63.8MHz Fig:Surfacecoilat405kHz Fig:Arraycoilresonanceat405kHz

In-housebuiltcoils

Solenoidcoilworkingatdifferentfieldfrequency

Fig:Earthfield,1.6kHz Fig:4.5mT,215kHz Fig:9.5mT,405kHz

HFSS Design steps

•  Modelling•  Assigningboundaries•  ExcitaCon•  MeshoperaCon•  Analysis• OpCmetrics• RadiaCon

Wrist Phantom:

SingleloopSpiralcoil

H-Field at XY Plane

Wrist model: Spiral lumped

Coil characterizaBon using NA E5063A

Fig: surface coil of loop innerdiameter=13cmisdividedinto fourbreak point at each point 48pF isp laced to get resonance at64.54MHz

Fig:Na-23surfacecoilofloopinnerdiameter=12cmisdivided intofourbreak point at each point 470pF isplaced and the pointed red andyellow arrow indicaCng the tuningand matching circuit to getresonanceat105.34MHz

Frequency response of the coil

Fig: Assembled four channel wrist coil

Fig:Interfacesolenoidcoiltothenetworkanalyzertovalidatetheworkingfrequency.CoilresonaCngat215kHzwithagain24dB

Experimental setup for coil characterizaBon

Figure1:ExperimentalsetupforAFcoilcharacterizaCon Figure2:AFcoil

Data 1

0 1000 2000 30000

5

10

15

Frequency in Hz

Mag

netic

fiel

d in

ute

sla

Demo: coil characterizaBon using NA

•  AmagneCcfieldpassingthroughtheprobeloopgeneratesavoltage

•  AccordingtoFaradayslaw,whichstatesthattheinducedvoltageisproporConaltotherateofchangeofmagneCcfluxthroughacircuitloop•  Atverylowfrequencies,avoltagewouldbeinduceddirectlyintheinternalloopconductor•  Athighfrequency,avoltageistheninducedintheoutersheathloop,andthisappearsacrossthesheathgap

Radio frequency amplifier

• RFamplifier:lowlevelinputsignalupfrommilli-wacrangetoalevelhighleveloutputsignal

ElementTrapcircuit

withdiode

RFamp

Surfaceloopcoil

•  RFAcircuitlevelschemaCc,amplifierstageconsistsof

•  Input/outputMatchingnetwork:responsibleformatchingthesystem50ohmimpedancewiththelowimpedancesoftheRFtransistorsformaximumpowertransfer.

•  Couplinganddecouplingcomponent:TransfertheRFandDCenergyintheappropriatedirecCons

•  Transistor:AmplifiestheRFsignal

hcp://www.cpcamps.com/introducCon-to-nmr-mri-amplifiers.html