A measure of the noise performance of an amplifier or chain of amplifiers such as a MR receiver. In MR systems the preamplifier should have a very low noise figure to prevent significant degradation of the signal to noise ratio of the MR signal. Noise figure is a ratio in dB's, and is given by: 20 log [Vo/(ViG)] where Vi is the input thermal noise voltage, Vo is the amplifier output noise level and G is the voltage gain of the amplifier (when the input and output impedance's of the amplifier are equal).

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.

The phased array coils operate typically as receive only coils. In that case, the in the MRI device implemented body coil act as the transmitter and sends the radio frequency energy to generate the excitation pulses. State-of-the-art array coil systems include the use of 4 (up to 32) coils with separate receivers. This method is often referred to as a phased array system, although the signals are not added such that the signal phase information is included. The use of phased array coils allows the decreasing of the number of signal averages, which shortens the scan time by high SNR and resolution.
High-sensitivity RF surface coils and digital processing algorithms have been developed that speed up image acquisition and reconstruction during the MRI scan.
Fast parallel imaging techniques, for example sensitivity encoding (SENSE), 'Partially Parallel Imaging with Localized Sensitivity' (PILS), Simultaneous Acquisition of Spatial Harmonics (SMASH) or Array Spatial Sensitivity Encoding Technique (ASSET) use phased array multichannel coils to further improve spatial and temporal resolution. The sensitivity profile of a phased array coil element is measured by a separate low resolution 3D acquisition over the entire field of view in the case of a SENSE acquisition. For an mSENSE measurement, a self-calibration acquires some of the missing lines in the center of the k-space.
Also called linear array coil or synergy surface coil.

See also the related poll result: '3rd party coils are better than the original manufacturer coils'

The portion of a MR spectrometer comprising the sample container and the RF coils, with some associated electronics. The RF coils may consist of separate receiver and transmitter coils in a crossed coil configuration, or, alternatively, a single coil to perform both functions.

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 90°. 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 √2, can be achieved.

See also the related poll result: '3rd party coils are better than the original manufacturer coils'