Why Quadrature RF Coils Are Preferred?
1. Higher Signal-to-Noise Ratio (~40% improvement)
A quadrature coil uses two coils placed 90° apart, receiving signals in two orthogonal directions.
These two independent signals combine constructively, giving:
√2 (≈ 1.41×) higher SNR
Better image quality, especially for low-signal tissues.
More SNR = better resolution, faster scans, or both.
2. Better Sensitivity to Circularly Polarized MR Signal
The MR signal emitted by precessing protons is circularly polarized.
A single coil picks up only one component of this circular motion.
A quadrature coil picks up both components, matching the physics of precession much better → more efficient signal capture.
3. Reduced Noise
Noise is random and uncorrelated between the two coils, while MR signal is correlated.
When signals combine:
Signal adds coherently
Noise adds incoherently
➡️ Improves SNR without increasing noise.
4. Less Transmit Power Needed
In transmit mode, quadrature coils create a rotating B1 field, which couples better with precessing spins.
This gives:
Shorter RF pulses
Lower power deposition
Improved flip-angle uniformity
➡️ Beneficial for SAR-limited sequences like fast spin echo.
5. Better Homogeneity
Quadrature excitation produces a more uniform B1 field compared to linear coils → fewer artifacts and better fat suppression or uniform contrast.
🔍 Summary
Quadrature RF coil arrangement is preferred because it provides ~40% higher SNR, better coupling with circularly-polarized MR signal, reduced noise, lower RF power requirements, and improved B1 field homogeneity.
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