Is Echo An EPI gradient?

Is Echo An EPI gradient?

Echo planar imaging (EPI) is performed using a pulse sequence in which multiple echoes of different phase steps are acquired using rephasing gradients instead of repeated 180-degree radiofrequency pulses following the 90°/180° in a spin echo sequence.

What does EPI mean in MRI?

GE – Echo planar The echo planar (EPI) is the fastest acquisition method in MRI (100 ms / slice), but with limited spatial resolution. It is based on: an excitation pulse, possibly preceded by magnetization preparation.

What is the EPI factor?

The number of k-space lines (echoes) collected in a single shot is called the “Echo Train Length (ETL)” by GE and Canon; the “EPI factor” by SIemens and Philips; and the “shot factor” by Hitachi. The regions of k-space divided up by each shot of a multi-shot sequence are called segments.

What is echo planar imaging used for?

Echo-planar imaging facilitates rapid evaluation of cardiac function and anatomy. Cine imaging of the heart is performed with GRE echo-planar imaging over multiple cardiac cycles. When single-shot echo-planar imaging is used, electrocardiographic gating is not required.

How does gradient echo work?

The gradient echo is generated by the frequency-encode gradient, except that it is used twice in succession, and in opposite directions: it is used in reverse at first to enforce transverse dephasing of spinning protons and then right after, it is used as a readout gradient (like in spin-echo MRI) to re-align the …

What is echo spacing?

1. n. [Formation Evaluation] The time between each echo in a nuclear magnetic resonance (NMR) measurement. The time is also the time to the first echo and is therefore an important parameter in defining the fastest relaxation time that can be measured.

What is single shot EPI?

Typically, single-shot EPI or spiral gradient echo is used, without readout window on the same order as the echo time, making the signal especially sensitive to magnetic susceptibility effects. The result of such effects is typically image blurring, distortions of the imaged tissues, and signal dropouts.

What are advantages of using gradient echo sequences?

The advantages of low-flip angle excitations and gradient echo techniques are faster acquisitions, new contrasts between tissues and a stronger MR signal in case of short TR.

What is echo planar (epi)?

The echo planar (EPI) is the fastest acquisition method in MRI (100 ms / slice), but with limited spatial resolution. It is based on: an excitation pulse, possibly preceded by magnetization preparation

What is the difference between spin echo and epi?

The diffusion weighted EPI sequence is very similar to a spin echo sequence. Both use a 90° degree excitation pulse followed by a 180° refocusing pulse. The difference lies in a unique gradient activation at different amplitudes prior to the EPI gradient configuration.

What is the range of gradient amplitudes used in EPI?

In EPI, much larger gradient amplitudes are used. A gradient of about 2.5 gauss/cm is typical, but human imagers with gradient amplitudes in excess of 5 gauss/cm are achievable.

What is the path of k-space scanning for an alternating gradient epi?

In the case of an alternating gradient (blipped and nonblipped EPI), k-space will be scanned from left to right and back, with each echo. At the same time, the phase encoding gradient may be permanent and constant (nonblipped) giving a zigzag global trajectory, or intermittent (blipped) at each echo onset, giving a rectilinear trajectory.