MRI hardware includes the electrical and mechanical components of a scanning device.
The main hardware components for the MRI machine are:
The magnet establishing the B0 field to align the spins.
Within the magnet are the gradient coils for producing variations in B0 in the X, Y, and Z directions to make a localization of the received data possible.
Within the gradient coil or directly on the object being imaged is the radio frequency (RF) coil. This RF coil is used to establish the B1 magnetic field necessary to excite the spinning nuclei. The RF coil also detects the signal emitted from the spins within the object being imaged.
The RF amplifier increases the power of the pulses.
The analog to digital converter converts the received analog raw data into digital values.
Depending on the design of the device and the body part being imaged the patient is positioned inside the magnet (e.g. on a movable table or standing upright).
The MRI scan room is surrounded by a RF shield (Faraday cage).
In addition, a computer console, a display, and a film printer belong to the MRI equipment.

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

Pulse sequences, designed to be insensitive to flow, e.g. at every even echo, a spin echo sequence is not flow sensitive. Velocity compensation is achieved by using gradients, which are either symmetrical around a 180° pulse and switched on twice as is the case for motion compensated spin echo pulse sequences, or two antisymmetrical gradient lobes without 180° pulse, which is the way to produce a velocity compensated gradient echo pulse sequence.
The signal of the second echo (and all other even echoes) is independent of the velocity of the object. Thus, velocity-based motion effects stemming from the entire voxel or from spins within a voxel (intravoxel incoherent motion) are suppressed with such pulse sequences.
If higher order motion is relevant, as it may be in turbulent jets across valves, acceleration and jerk effects can also be compensated for by the use of appropriate combinations of gradient- and radio frequency pulses.
With the increasingly stronger gradients, echo times in MR systems can be shortened to the point at which effects other than velocity effects hardly ever become relevant.

Multi echo imaging sequences use a series of echoes acquired as a train following after a single excitation pulse. Multiple symmetrical or asymmetrical echoes can be acquired, typically T2 weighted. In spin echo imaging, each echo is formed by a 180° pulse, but also a FSE (TSE, RARE) or EPI sequence can be used. As a difference to a normal fast spin echo sequence, in multi echo imaging, separate images are produced from each echo of the train with different T2 weightings. The signal height reduces with transverse relaxation. This drop in signal can be used to calculate a pure T2 image.

See also Fast Spin Echo.

The phase shift is the loss of phase coherence in precessing spins. Vascular spins move at variable velocities; faster flow undergo a stronger phase shift than slower flowing spins.

(PRESS) Point resolved spectroscopy is a multi echo single shot technique to obtain spectral data. PRESS is a 90°-180°-180° (slice selective pulses) sequence. The 90° radio frequency pulse rotates the spins in the yx-plane, followed by the first 180° pulse (spin rotation in the xz-plane) and the second 180° pulse (spin rotation in the xy-plane), which gives the signal.
With the long echo times used in PRESS, there is a better visualization of metabolites with longer relaxation times. Many of the metabolites depicted by stimulated echo technique are not seen on point resolved spectroscopy, but PRESS is less susceptible to motion, diffusion, and quantum effects and has a better SNR than stimulated echo acquisition mode (STEAM).