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The spin-echo effect was discovered by Erwin Hahn when he applied two successive 90° pulses separated by short time period, but detected a signal, the echo, when no pulse was applied. This phenomenon of spin echo was explained by Erwin Hahn in his 1950 paper, [ 5 ] and further developed by Carr and Purcell who pointed out the advantages of ...
Neutron spin echo is a time-of-flight technique. Concerning the neutron spins it has a strong analogy to the so-called Hahn echo, [13] well known in the field of NMR.In both cases the loss of polarization (magnetization) due to dephasing of the spins in time is restored by an effective time reversal operation, that leads to a restitution of polarization (rephasing).
This transverse magnetisation refocuses to form a spin echo at a time T E. During the spin echo, a frequency-encoding (FE) or readout gradient is applied, making the resonant frequency of the nuclear magnetization vary with its location in the X direction. The signal is sampled n FE times by the ADC during this period, as represented by the ...
Each of the spin-echo signal is a sinc function of time, which can be described by = Where = + ¯ Here ¯ is the gyromagnetic ratio constant, and is the basic resonance frequency of the spin. Due to the presence of the gradient G , the spatial information r is encoded onto the frequency ω {\displaystyle \omega } .
Because T 2 relaxation involves only the phases of other nuclear spins it is often called "spin-spin" relaxation. 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 ...
The spin echo is a 90° pulse followed by a 180° pulse after a time period τ and is applied on the proton, the sensitive nucleus (designated, perhaps counter-intuitively, as the I spin, while the insensitive nucleus is the S spin; note, however, that the original paper on INEPT used the opposite designations). [1] Spin Echo
In the echo experiment, two short, intense pulses of radiofrequency magnetic field are applied to the spin ensemble at the nuclear resonance condition and are separated by a time interval of τ. The echo appears with a given amplitude at time 2τ. For each setting of τ, the maximum value of the echo signal is measured and plotted as a function ...
When the spins are rephased, they become coherent, and thus signal (or "echo") is generated to form images. 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.