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An MRI pulse sequence in magnetic resonance imaging (MRI) is a particular setting of pulse sequences and pulsed field gradients, resulting in a particular image appearance. [ 1 ] A multiparametric MRI is a combination of two or more sequences, and/or including other specialized MRI configurations such as spectroscopy .
Fluid-attenuated inversion recovery (FLAIR) [2] is an inversion-recovery pulse sequence used to nullify the signal from fluids. For example, it can be used in brain imaging to suppress cerebrospinal fluid so as to bring out periventricular hyperintense lesions, such as multiple sclerosis plaques.
If the inversion pulse is applied after a period t of dephasing, the inhomogeneous evolution will rephase to form an echo at time 2t. In simple cases, the intensity of the echo relative to the initial signal is given by e –2t/T 2 where T 2 is the time constant for spin–spin relaxation.
Fluid-attenuated inversion recovery (FLAIR) is a magnetic resonance imaging sequence with an inversion recovery set to null fluids. For example, it can be used in brain imaging to suppress cerebrospinal fluid (CSF) effects on the image, so as to bring out the periventricular hyperintense lesions, such as multiple sclerosis (MS) plaques. [ 1 ]
Spin echo pulse sequence and magnetization decay animation. T 2 values are generally much less dependent on field strength, B, than T 1 values. Hahn echo decay experiment can be used to measure the T 2 time, as shown in the animation below. The size of the echo is recorded for different spacings of the two applied pulses.
An inversion recovery (IR) sequence is used to null the signal from normal myocardium. Myocardial viability can be assessed by the degree of transmural enhancement. Cardiomyopathic, inflammatory and infiltrative diseases may also have distinctive patterns of non-ischemic LGE. [22] [23]
A BIR-4 pulse is designed simply as two BIR-1 pulses back-to-back. For a 180-degree excitation (inversion), the second BIR-1 sequence is performed with B effective initially pointing along the –y-axis, sweeps to the +z-axis, flips to the
The generic FLASH technique emerges as a gradient echo sequence which combines a low-flip angle radio-frequency excitation of the NMR signal (recorded as a spatially encoded gradient echo) with a rapid repetition of the basic sequence. The repetition time is usually much shorter than the typical T1 relaxation time of the protons in biologic ...