Image gradient

The echo phase does not depend on the initial position of the nuclei, only on their displacement, vA, occurring in the interval between the gradient pulses. Analysis of the phase of the echo yields a measure of flow velocity in a bulk sample. Spatial resolution is easily obtained by the incorporation of additional imaging gradients. 

Fig. 2.6.10 Specialized experimental set-up for microfluidic flow dispersion measurements. Fluid is supplied from the top, flows via a capillary through the microfluidic device to be profiled and exits at the bottom. The whole apparatus is inserted into the bore of a superconducting magnet. Spatial information is encoded by MRI techniques, using rf and imaging gradient coils that surround the microfluidic device. They are symbolized by the hollow cylinder in the figure. After the fluid has exited the device, it is led through a capillary to a microcoil, which is used to read the encoded information in a time-resolved manner. The flow rate is controlled by a laboratory-built flow controller at the outlet [59, 60].

Fig. 4.2.3 PGSE timing diagram where Gz denotes both the slice select and the pulsed, sinusoidal shaped displacement encoding gradient and Greacj displays the transverse imaging gradient.

Fig. 4.5.5 Pulsed field gradient sequences to obtain velocity and diffusion data (a) spin-echo (PGSE) and (b) stimulated-echo (PGSTE). The application of imaging gradients C Gy and Gz allows the measurement of velcocity maps and spatially-resolved diffusion coefficients and size distribution in emulsions.

A second imaging gradient (Gy) is added in order to obtain a spatial map of the displacements. A notable feature of the stimulated echo protocol is that during the flow encoding time, A, the magnetization is stored along the z axis and is subject to the longitudinal... 

Fig. 5.3.6 j oint spatial-velocity images of xenon undergoing Poiseuille flow in a pipe (id = 4 mm, Vave = 27 mm s 1, D = 8 mm2 s 1) at 0.7 atm recorded with a protocol shown in Figure 5.3.4(A). Only particles at walls are selected by the edge enhancement filter . A modified imaging gradient time duration... 

Camera raw image contains the iris and its surroundings. Thus, the iris localization methods must be applied to extract the valuable iris texture information available within the image. Localization of both inner (i.e., between the pupil and the iris) and outer (i.e., between the iris and the sclera) iris boundaries makes use of local image gradient estimation. Consequently, we approximate the shape of inner and outer boundaries by two non-concentric circles. Figure 2 presents the camera raw image with iris both circular boundaries localized. 

Fig. 2.3.10 [Bliil] Magnetic fields used in NMR spectroscopy and imaging, (a) In spectroscopy the field is required to be homogenous over the sample, (b) In imaging gradients are applied. Their strength determines the change of magnetic field with space and thus the spatial resolution.

Equation (12.65) represents the variation of the photoactive compound on account of exposure. This expression shows that the latent image gradient dm/dx... 

Orientation assignment is made to aU Pols based on local image gradient directions. All fumre operations are performed on image data that have been transformed relative to the assigned orientation, scale and location for each Pol, thereby providing invariance for these transformations. 

Local image gradients are measured at the selected scale in the region around each Pol. These are transformed into a Pol descriptor of 128 elements that allows Pols to be highly... 

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