What is spin echo used for?

Ray Ballinger et al. Spin-echo pulse sequences are one of the earliest developed and still widely used (in the form of fast spin-echo) of all MRI pulse sequences. The pulse sequence timing can be adjusted to give T1-weighted, proton density, and T2-weighted images.

What is the difference between spin echo and fast spin echo?

The spin echo (SE) sequence uses an additional, 180-degree pulse, to flip protons and generate an echo as they rephase. This negates T2* effects from magnetic field inhomogeneity. It also provides better signal but is slower. Fast spin echo (FSE) uses many successive 180-degree pulses to speed acquisition.

What is the spin echo experiment?

In magnetic resonance, a spin echo is the refocusing of spin magnetisation by a pulse of resonant electromagnetic radiation. Modern nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) make use of this effect.

What is the benefit of a spin echo sequence?

Fast spin echo sequence The improvement in imaging time is most powerful when used with a rectangular field of view (e.g. spinal imaging), and the phase encoding direction is chosen to correspond with the smallest matrix size dimension. This minimizes the number of excitation pulse repetitions required per image.

Why is it called spin echo?

In fact, spin echoes are formed when two successive RF-pulses of any flip angle are employed! Hahn, in his original paper, used two 90° pulses. When flip angles other than 90° and 180° are employed, the resultant spin echo is sometimes referred to as a Hahn echo.

What does the MR scanner tune in order to select a slice for excitation?

The slice-select gradient sets up a magnetic field gradient across the patient, changing the Larmor frequency of the protons in the entire body. By matching the excitation pulse to the frequency of protons at a particular position, the scanner can excite a thin slice of the body.

What is echo train length in MRI?

Echo train length (ETL) is the single most important parameter. In general, image acquisition time is inversely proportional to ETL. In other words, if a CSE sequence with a certain TR/TE/spatial resolution takes 8 minutes to perform, a FSE sequence with ETL=8 would take only 1 minute.

Why is a 180 RF pulse applied in spin echo imaging in MRI after a 90 RF pulse?

After a 90° RF pulse, spins dephase and transverse magnetization decreases. If we apply a 180° RF pulse, spins rephase and transverse magnetization reappears.

What type of flip angle is used in spin echo?

90 degrees
The flip angle is usually at or close to 90 degrees for a spin-echo sequence but is less on gradient-echo sequences, commonly varying over a range of 10 to 80 degrees (usually denoted by α).

How is a spin echo generated?

What is T2 star?

T2*-weighted imaging is an MRI sequence to quantify observable or effective T2 (T2* or “T2-star”). In this sequence, hemorrhages and hemosiderin deposits become hypointense.

What happens after the RF pulse is sent into the patient?

As the RF electromagnetic radiation is sent through the patient, the atomic nuclei in the body will absorb the energy. This absorption of energy causes nuclei to change the direction of their spin. You can intuitively understand this with the model shown above.

What is the Te of a spin echo?

A single RF pulse generates a free induction decay (FID), but two successive RF pulses produce a spin echo (SE). The time between the middle of the first RF pulse and the peak of the spin echo is called the echo time (TE).

What are the disadvantages of weighted spin echo sequences?

Choosing the right sequence parameters (TR and TE) will produce images weighted in T1, T2 or proton density. The major disadvantage with T2 weighted spin echo sequences is linked to long TR resulting in prohibitive acquisition times.

What kind of spin echo does Hahn use?

Hahn, in his original paper, used two 90° pulses. When flip angles other than 90° and 180° are employed, the resultant spin echo is sometimes referred to as a Hahn echo. No supplementary material yet.

When to use dir or FSE spin echo?

Double inversion recovery (DIR) fast spin-echo (FSE) cardiovascular magnetic resonance (CMR) sequences are used clinically for black-blood T2-weighted imaging. However, these sequences suffer from slice inefficiency due to the non-selective inversion pulses.