The signal height. The greater the amplitude of the signal, the larger the number of protons in the image and the brighter the signal will appear.

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.

During the MRI scan an augmentation of T waves is observed at fields used in standard imaging but this possible MRI side effect is completely reversible upon removal from the magnet. A field strength dependent increase in the amplitude of the ECG in rats has been observed during exposure to high homogeneous stationary magnetic fields, but this side effect is not transferable to standard imaging situations for humans.

The minimum level at which augmentation can be observed is 0.3 T and increases by higher field strength. An augmentation in T-wave amplitude can occur instantaneously and is immediately reversible after exposure to the magnetic field ceased. There should be no abnormalities in the ECG in the later follow-up. Augmentation of the signal amplitude in the T-wave segment may result from superimposed electrical potential. No circulatory alterations coincide with the ECG changes. Therefore, no biological risks are believed to be associated with them.

For more MRI safety information see also Contraindications and MRI Risks.

Adiabatic RF pulses are amplitude and frequency modulated pulses that are insensitive to the effects of B1-inhomogeneity and frequency offset (conventional RF pulses used in MRI are only amplitude modulated). Due to an extended application time adiabatic RF pulses are mostly used in NMR imaging applications.

A microscopic group of spins, which resonate at the same frequency. The spin precesses around a circle in the xy-plane and the net magnetization is the length, amplitude or magnitude of the magnetization vector Mxy: the quantity normally represented on a pixel-by-pixel basis in a MR image (thus amplitude or magnitude image).