What is gradient echo pulse sequence?
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 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 is GRE sequence in MRI?
Abstract. The sequence of a multiecho gradient recalled echo (GRE) T2 -weighted imaging (T2 WI) is a relatively new magnetic resonance imaging (MRI) technique. In contrast to T2 relaxation, which acquires a spin echo signal, T2 relaxation acquires a gradient echo signal.
Is GRE T1 or T2?
Because the spoiled-GRE technique is specifically designed to disrupt transverse (T2) coherences, its major benefit and use is in producing T1-weighted images. Nevertheless, both spin density- and T2*-weighting can be achieved by appropriate selection of parameters.
What is pulse sequence in NMR?
In Fourier transform NMR spectroscopy and imaging, a pulse sequence describes a series of radio frequency pulses applied to the sample, such that the free induction decay is related to the characteristic frequencies of the desired signals.
What is T2 * sequence?
T2*-weighted sequences are used to depict paramagnetic deoxyhemoglobin, methemoglobin, or hemosiderin in lesions and tissues.
What is a gradient echo sequence?
The sequences of the gradient echo type allow to achieve very short repetition times, as the acquisition of an echo corresponds to the acquisition of a k-space line, and this acquisition can be made quick by increasing the amplitude of the gradients of rephasing and reading.
What is the flip angle of an echo sequence?
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 does the Hahn echo sequence work?
In 2020 two teams demonstrated that when strongly coupling an ensemble of spins to a resonator, the Hahn pulse sequence does not just lead to a single echo, but rather to a whole train of periodic echoes. In this process the first Hahn echo acts back on the spins as a refocusing pulse, leading to self-stimulated secondary echoes.
What is the difference between in-phase and out-of-Phase (OOP) echo sequences?
In-phase (IP) and out-of-phase (OOP) sequences correspond to paired gradient echo sequences using the same repetition time (TR) but with two different echo times (TE). This can detect even microscopic amounts of fat, which has a drop in signal on OOP compared to IP.