The quadrature detector is a part of the receiver that converts the high-frequency MRI signal to a lower frequency. This phase sensitive detector or demodulator detects the components of the signal in phase with a reference signal and 90° out of phase with the reference signal. The modulated signal contains i.e. the frequency range across the field of view encoded by the frequency encoding gradient. This may be performed by either analog or digital means.

Part of the receiver that demodulates the RF signal and converts it to a lower frequency signal. Most detectors are phase sensitive (e.g., quadrature detector / demodulator) and will also give phase information about the RF signal.

Out of phase component of the signal from a quadrature detector.

Detector that detects the phase of the signal relative to the phase of a reference oscillator. Phase sensitive detectors are used in MR transmitters (where they form part of the frequency synthesis pathway) and MR receivers (where they are used to down-convert the MR signal to audio-frequencies prior to digitization). This device type includes modulators, demodulators and mixers.

See Quadrature Detector.

Product detector or 'doubly balanced mixer (DBM)' is an electrical device to combine two signals. In MRI, used in the quadrature detector.