Hardware components from MRI systems. The radio frequency (RF) amplifier increases the power (measured in Watt) of the pulses from mW to kW and the gradient amplifier increases the power of the gradient pulses for the gradient coils.

See also Hardware.

A device that amplifies very low-level signals. A preamplifier is generally placed close to its signal source and has a very low noise figure as it is the principal determinant of electronic noise within the system. Preamplifiers used in NMR systems usually have a 50 ohm input impedance, and require a matching network to interface to the RF coil, although preamplifiers with high input impedance may be used with surface coils. Such devices typically use a field effect transistor (FET) as their input stage.

In MRI systems, the gradient amplifier increases the energy of the signal before it reaches the gradient coils, in a way, that the field strength is intense enough to produce the variations in the main magnetic field for localization of the later received signal. Three gradient coils normally require three gradient amplifiers. As all amplifiers, gradient amplifiers produce heat, which requires cooling.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'

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).

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.