( TIR / TIRM / IR-TSE - Inversion Recovery Turbo Spin Echo / FIR - Fast Inversion Recovery)
A turbo / fast spin echo sequence with long TI for fluid suppression (FLAIR) or with short TI for fat suppression (STIR). This sequence allows for a true inversion recovery display that shows the arithmetic sign of the signal.
TIRM means a turboIR with a magnitude display.

See also Inversion Recovery, Inversion Recovery Sequence and Fast Spin Echo.

Vibrations of the gradient coil support structure create sound waves. These are caused by the interactions of the magnetic field created by pulses of the current through the gradient coil with the main magnetic field in a manner similar to a loudspeaker coil. The sounds made by the scanner vary in volume and tone with the type of procedure being performed.
Sound pressure is reported on a logarithmic scale called sound-pressure level, expressed in decibel (dB) referenced to the weakest audible 1 000 Hz sound pressure of 2 * 10^-5 pascal (20 micropascal). Sound level meters contain filters that simulate the ear's frequency response. The most commonly used filter provides what is called 'A' weighting, with the letter 'A' appended to the dB units, i.e. dBA.
MRI system noise levels increase with field strength. Disposable earplugs and/or headphones for the patient are recommended in high-field systems. Noise-canceling systems and special earphones are available, and active acoustic control systems were developed, e.g. softtone, pianissimo. A sequence with low noise gradient pulses is also called 'whisper sequence'.

See also Phon and Decibel.

An image artifact is a structure not normally present but visible as a result of a limitation or malfunction in the hardware or software of the MRI device, or in other cases a consequence of environmental influences as heat or humidity or it can be caused by the human body (blood flow, implants etc.). The knowledge of MRI artifacts (brit. artefacts) and noise producing factors is important for continuing maintenance of high image quality. Artifacts may be very noticeable or just a few pixels out of balance but can give confusing artifactual appearances with pathology that may be misdiagnosed.
Changes in patient position, different pulse sequences, metallic artifacts, or other imaging variables can cause image distortions, which can be reduced by the operator; artifacts due to the MR system may require a service engineer.
Many types of artifacts may occur in magnetic resonance imaging. Artifacts in magnetic resonance imaging are typically classified as to their basic principles, e.g.:
Several techniques are developed to reduce these artifacts (e.g. respiratory compensation, cardiac gating, eddy current compensation) but sometimes these effects can also be exploited, e.g. for flow measurements.

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

(BTFE) A gradient echo pulse sequence with a balanced gradient waveform and data acquisition after an initial preparation pulse for contrast enhancement.

See Steady State Free Precession (SSFP) and Balanced Sequence.

Bipolar gradients are two gradients with the same magnitude but opposite gradient direction. A bipolar gradient pulse is produced if one of the bipolar gradients is switched e.g., in negative direction and then switched in the opposite direction for an equivalent amount of time.
Bipolar gradients are used e.g. in phase contrast and diffusion weighted sequences. A bipolar gradient pulse pair produces a phase shift, which depends on the velocity component along this gradient. Motion along a bipolar gradient pulse pair results in a flow-induced phase shift of the transverse magnetization. The bipolar gradient pulse pair will not affect stationary spins. The amount of phase shifts depends on the area of each gradient pulse, and distance between the pulses. An echo occurring after such a gradient is flow compensated for velocity. A slight shift in the balance of this gradient will introduce a defined flow sensitivity of the pulse sequence.