What is a blip on an MRI?

These are caused by abrupt changes in the magnetic susceptibility that typically occur near air/tissue interfaces and may result in substantial image distortions and signal losses.

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 is 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 the difference between spin echo and gradient echo?

A spin echo (SE) is produced by pairs of radiofrequency (RF) pulses, whereas a gradient echo (GRE) is produced by a single RF pulse in conjunction with a gradient reversal. The formation of a GRE is illustrated schematically.

What is a gradient echo sequence?

Gradient echo sequences (GRE) are an alternative technique to spin-echo sequences, differing from it in two principal points: utilisation of gradient fields to generate transverse magnetisation. flip angles of less than 90°

What is the TR range for T1?

The range depends on the tissues being imaged as well as the field strength of the MR system. T1 relaxation times lengthen (increase) as field strength increases. At 1.5 T, when acquiring T1-weighted images of the brain, the TR is usually between 400 and 550 msec.

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 is gradient echo sequence in MRI?

Gradient echo sequences (GRE) are an alternative technique to spin-echo sequences, differing from it in two principal points: utilization of gradient fields to generate transverse magnetization. flip angles of less than 90°

What is gradient echo used for?

As with spin-echo sequences, magnetization preparation can be added to gradient-echo sequences to alter image contrast. Gradient echo sequences are widely used for numerous applications such as 3D perfusion imaging, functional MRI, cardiac imaging and MR angiography.

Why do we use gradient echo?

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 …