Velocity encoding gradient

Fig. 2.8.1 Rf and gradient pulse sequence used encoding is along the x axis. By changing the to encode for velocity in a two-dimensional direction of the velocity encoding gradient image in the (x, y) plane normal to the slice pulse pair of duration 6 other directions for direction z. In the example shown the velocity velocity components can be measured.

Fig. 4.2.5 Unaliased (A) and aliased (B) velocity images for a 0.6% aqueous carboxy-methylcellulose solution obtained by MRI. The vertical axes represent the data obtained in the velocity encoded direction and the horizontal axis represents data obtained in the spatially encoded direction. Aliasing is achieved by setting the velocity encode gradients so large that the maximum phase evolution of a given fluid element for a pulsed gradient step exceeds Ji or 2jt...

In order to obtain spatial resolution of the molecular translations within each voxel, it is necessary to combine the velocity-encoding gradient sequence shown in Section 3.1.1 with a standard imaging sequence such as frequency or phase encoding. The displacement distribution function, P A (R), must now be generalized to a spatial-displacement joint density function Aso that it describes the total number of spins located at r with displacement R during time A 28... 

In order to expand the velocity-encoding pulse sequence to two-component velocity measurement in a two-dimensional domain, we can superimpose another series of velocity-encoding gradients on the x-axis in Fig. 11, where phase-encoding is applied for spatial resolution. For steady-state flowing conditions, however, it may be faster and more convenient to use two different pulse sequences independently. After the data for the z-component velocity field... 

Correct velocity encoding gradient (VENC) adjusted to the estimated maximum velocity (possible detectable phase shift (-7r)-n)... 

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