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Fast spin echo (RARE, FAISE or FSE [10] [11] [12]), also called turbo spin echo (TSE) is an MRI sequence that results in fast scan times. In this sequence, several 180 refocusing radio-frequency pulses are delivered during each echo time (TR) interval, and the phase-encoding gradient is briefly switched on between echoes. [ 13 ]
Unlike spin echo, gradient echo does not need to wait for transverse magnetisation to decay completely before initiating another sequence, thus it requires very short repetition times (TR), and therefore to acquire images in a short time. After echo is formed, some transverse magnetisations remains.
Gradient RGB/CMY color wheel Seven-color and twelve-color color circles from 1708 (attributed to Claude Boutet) Wilhelm von Bezold's 1874 Farbentafel. A color wheel or color circle [1] is an abstract illustrative organization of color hues around a circle, which shows the relationships between primary colors, secondary colors, tertiary colors etc.
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 ...
When the echo is recorded close to the middle of the interval (TE ≈ TR/2, as is usually the case), the final term e−TE/T2 depends on T2, not T2*. Thus, bSSFP sequences behave more like spin echo than gradient echo sequences in that they do not have T2*-dependence.
Instead, the gradient echo uses magnetic gradients to manipulate the spins, allowing the spins to dephase and rephase when required. After an excitation pulse (usually less than 90 degrees), the spins are dephased after a period of time (due to free induction decay ) and also by applying a reversed magnetic gradient to decay the spins. [ 2 ]
Visual representation of the spin of a proton under a constant magnetic field B 0. Visualization of the and relaxation times. The transverse (or spin-spin) relaxation time T 2 is the decay constant for the component of M perpendicular to B 0, designated M xy, M T, or .
Domain coloring plot of the function f(x) = (x 2 − 1)(x − 2 − i) 2 / x 2 + 2 + 2i , using the structured color function described below. In complex analysis, domain coloring or a color wheel graph is a technique for visualizing complex functions by assigning a color to each point of the complex plane. By assigning points on the ...