A coil that produces an RF field with circular polarization. The RF power received from the RF power amplifier comes in two signals (quadrature detection), which have a phase difference of 90Â°. The RF transmit coil converts the power into a circularly polarized RF magnetic field.
Quadrature coils can be used as both, transmit and/or receive coil.
When used as a transmitter coil a factor of two power reduction over a linear coil results; as a receiver an increase in SNR of up to a factor of âˆš2, can be achieved.
Quadrature detection is used in magnetic resonance imaging as well as in Doppler ultrasound and is also called quadrature demodulation or phase quadrature technique.
With this phase sensitive demodulation technique the complex demodulated signal is separated into two components. One is called the real channel; the second part is called the imaginary channel and is located 90° away from the real channel. The signals from both channels are combined to produce a single set of quadrature detected real and imaginaryspectra. In MRI, the parts of the demodulated MR signal are further processed by Fourier transformation analysis. All information on the MR signal components e.g. amplitude, phase, and frequency is given by this quadrature detection combined with Fourier analysis.
A measure of the non-spherical distribution of electrical charge possessed by nuclei with a nuclear spin number greater than 1/2. The resulting interaction with electric field gradients in the molecule can lead to a shortening of relaxation times and a broadening of spectral lines.