What is a pulse sequence in MRI?

An MRI pulse sequence is a programmed set of changing magnetic gradients. Each sequence will have a number of parameters, and multiple sequences grouped together into an MRI protocol.

What is pulse sequence diagram?

A pulse sequence diagram (PSD) illustrates the sequence of events that occur during magnetic resonance imaging (MRI). It is a timing diagram showing the radio frequency (RF) pulses, gradients, and echoes.

What are the different pulse sequences?

The most important ones are the spin echo (SE) sequence, the inversion recov- ery (IR) sequence, and the gradient echo (GRE) sequence, which are the basic MR pulse sequences.

What is the first step of MRI scan sequence?

Thus, the first step in MRI is to set up a strong magnetic field (called B0) along the axis of the scanner. The tendency to align along the magnetic field is relatively weak, so random vibrations and collisions of protons within tissue will keep most of them from actually lining up with B0.

How many main categories are there in an MRI sequence?

There are two main sequence families, depending on the type of echo recorded: spin echo sequences and gradient echo sequences. There are two main sequence families, depending on the type of echo recorded: spin echo sequences, characterized by the presence of a 180° rephasing RF pulse.

What is the purpose of the 90 degree pulse in MRI?

If the protons are initially aligned along the z (vertical) axis, and we apply a pulse along the x axis for the right amount of time, we can rotate the magnetization from the z-axis onto the y-axis. This is referred to as a 90-degree pulse, since the magnetization direction is turned by 90 degrees.

What is spin echo pulse sequence in MRI?

The spin echo sequence is made up of a series of events : 90° pulse – 180° rephasing pulse at TE/2 – signal reading at TE. This series is repeated at each time interval TR (Repetition time). With each repetition, a k-space line is filled, thanks to a different phase encoding.

How do you identify a MRI sequence?

The best way to tell the two apart is to look at the grey-white matter. T1 sequences will have grey matter being darker than white matter. T2 weighted sequences, whether fluid attenuated or not, will have white matter being darker than grey matter.

What is T1 and T2 image in MRI?

The most common MRI sequences are T1-weighted and T2-weighted scans. T1-weighted images are produced by using short TE and TR times. The contrast and brightness of the image are predominately determined by T1 properties of tissue. Conversely, T2-weighted images are produced by using longer TE and TR times.