The talk introduces the basics of RF coils as required by MIRC

1. Radio Frequency coil
Presented by
Darshan K S

2. 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 = ​1/2 𝜋√⁠ 𝐿 𝐶

3. d
RF coils
=
d =
d =
d =
d =
d =
d =
d =
.
d =
d =
d =
d =
d =
d =
d =
d =
.
Fig 1: Biot Savart hold good, for low frequencies
and region close to coil
• Generated magneCc field (B-field ) can be calculated
by the law of ‘Biot-Savart’ equaCon
• dB = ​ 𝜇0 /4 𝜋 ​ 𝐼 𝑑𝑙∗ 𝑟/|𝑟|^3

4. 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: Sample birdcage coil
Design
• Surface coil
Ø N=1
Ø Loop Diameter =2.6cm
Ø Inductance

5. RF Coils
Fig 1: Birdcage coil
Fig 2: Surface loop
Fig 3: Phased array coil
Fig: Birdcage coil at 63.8MHz Fig: Surface coil at 405kHz Fig: Array coil resonance at 405kHz
In-house built coils
Solenoid coil working at different field frequency
Fig: Earth field, 1.6kHz Fig: 4.5mT, 215kHz Fig: 9.5mT, 405kHz

6. HFSS Design steps
• Modelling
• Assigning boundaries
• ExcitaCon
• Mesh operaCon
• Analysis
• OpCmetrics
• RadiaCon

7. Wrist Phantom:
Single loop
Spiral coil

8. H-Field at XY Plane

9. Wrist model: Spiral lumped

10. Coil characterizaBon using NA E5063A
Fig: surface coil of loop inner
diameter=13cm is divided into four
break point at each point 48pF is
placed to get resonance at
64.54MHz
Fig : Na-23 surface coil of loop inner
diameter=12cm is divided into four
break point at each point 470pF is
placed and the pointed red and
yellow arrow indicaCng the tuning
and matching circuit to get
resonance at 105.34MHz

11. Frequency response of the coil
Fig: Assembled four channel wrist coil
Fig: Interface solenoid coil to the network analyzer to validate
the working frequency. Coil resonaCng at 215 kHz with a gain 24dB

12. Experimental setup for coil characterizaBon
Figure 1: Experimental setup for AF coil characterizaCon Figure 2: AF coil
Data 1
0 1000 2000 3000
0
5
10
15
Frequency in Hz
Magneticfield
inutesla

13. Demo: coil characterizaBon using NA
• A magneCc field passing through the probe loop generates a voltage
• According to Faradays law, which states that the induced voltage is
proporConal to the rate of change of magneCc flux through a circuit
loop
• At very low frequencies, a voltage would be induced directly in the
internal loop conductor
• At high frequency, a voltage is then induced in the outer sheath loop,
and this appears across the sheath gap

14. Radio frequency amplifier
• RF amplifier : low level input signal up from milli-wac range to a level
high level output signal
Element
Trap
circuit
with diode
RF amp
Surface loop coil

15. • RFA circuit level schemaCc, amplifier
stage consists of
• Input/output Matching network:
responsible for matching the system 50
ohm impedance with the low impedances
of the RF transistors for maximum power
transfer.
• Coupling and decoupling component:
Transfer the RF and DC energy in the
appropriate direcCons
• Transistor: Amplifies the RF signal
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