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 schematic figures of a pulse sequence timing diagram illustrate the steps of basic hardware activity that are incorporated into a pulse sequence. Time during sequence execution is indicated along the horizontal axes. Each line belongs to a different hardware component. One line is needed for the radio frequency transmitter and also one for each gradient (G_s = slice selection gradient x, G_f = phase encoding gradient y, G_f = frequency encoding gradient z, also called readout gradient).
In picture 1, a timing diagram for a 2D pulse sequence is shown.
Slice selection and signal detection are repeated in duration, relative timing and amplitude, each time the sequence is repeated. A single phase encoding component is present each time the sequence is executed.
Additional lines are added for ADC (Analog to Digital Converter) and sampling. A gradient pulse is shown as a deviation above or below the horizontal line. Simultaneous component activities such as the RF pulse and slice selection gradient are indicated as a non-zero deviation from both lines at the same horizontal position. Simple deviations from zero show constant amplitude gradient pulse. Gradient amplitudes that change during the measurement, e.g. phase encoding are represented as hatched regions.

The second picture shows a timing diagram for a 3D pulse sequence.
Volume excitation and signal detection are repeated in duration, relative timing and amplitude, each time the sequence is repeated. Two phase encoding components are present, one in the phase encoding direction and the other in slice selection direction (irrespectively incremented in amplitude) in each time the sequence is executed. A description of the comparison of hardware activity between different pulse sequences.

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.

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Quick Overview
Please note that there are different common names for this artifact.

The received radio frequency signal is too strong, parts of the signal get lost by converting from analog to digital, resulting in a washed out image.

Auto-prescanning usually adjusts the amplification at the receiver in a way, that the received signal could be processed without any loss. Else the receiver gain must be corrected manually.

See also Data Clipping Artifact, Artifact Overview and Artifacts Reduction Index.