The portion of the MRI equipment that detects and amplifies the RF signals picked up by the receiver coil. Includes a preamplifier, MR signal amplifier, and demodulator. Phase sensitive detectors (electronic device in which the output is dependent on the instantaneous difference in phase between two input signals) are used to down-convert the MR signal to audio-frequencies prior to digitization.

See also MRI Equipment.

A coil, or antenna, positioned within the imaging volume and connected to the receiver circuitry that is used to detect or receive the MR signal from the patient as the disturbed spins relax back into their equilibrium distribution. Also called receive-only coil.
Special-purpose coils are designed to optimize the SNR from a given region of the body. State-of-the-art coil systems include the use of four or more coils with four separate receivers. This method is often referred to as a phased array system. Receiver coil types include also solenoid, planar, volume and quadrature coils. The quality of the MR images depends on the SNR of the acquired signal from the patient. SNR is of the utmost importance in obtaining clear images of the interior of the human body.

Time after exciting RF pulse during which FID is not detectable due to saturation of receiver electronics.

Quick Overview

A receiver turn on artifact (not a true MR signal) appears similarly like a FID signal artifact, except that they extend into the signal-free region, while the FID (a real MR signal) is confined to the projection of the sample along the readout axis.

FID artifacts cannot occur on gradient echo images, but receiver turn on is still possible on gradient echoes.

See also FID Signal Artifact.

(BW) Bandwidth is a measure of frequency range, the range between the highest and lowest frequency allowed in the signal. For analog signals, which can be mathematically viewed as a function of time, bandwidth is the width, measured in Hertz of a frequency range in which the signal's Fourier transform is nonzero.

A higher bandwidth is used for the reduction of chemical shift artifacts (lower bandwidth - more chemical shift - longer dwell time - but better signal to noise ratio). Narrow receive bandwidths accentuate this water fat shift by assigning a smaller number of frequencies across the MRI image. This effect is much more significant on higher field strengths. At 1.5 T, fat and water precess 220 Hz apart, which results in a higher shift than in Low Field MRI.
Lower bandwidth (measured in Hz) = higher water fat shift (measured in pixel shift).

See also Aliasing, Aliasing Artifact, Frequency Encoding, and Chemical Shift Artifact.