Additionally, MEDI uses the fact that changes in susceptibility follow the morphological boundaries and that the susceptibility map therefore should have gradients in the same locations as the magnitude image .
The phase images were also masked before they were supplied to the MEDI algorithm, using a threshold approach based on information from the magnitude image, to define the object region to be included in the susceptibility calculation.
We therefore used the intensity-weighted gradient magnitude image
to segment the necrotic core (characterized by a low gradient magnitude and a low intensity).
To detect the region of interest (ROI), after creating a magnitude image in K-space data, the task of separating the object from the background is processed.
This unwrapped phase image is used to create a phase mask that is used to multiply the original magnitude image to create novel contrasts in the magnitude image.
Figure 1 shows an example of (a) original face image, (b) gradient magnitude image
, and (c) the histogram of gradient magnitude.
In methods involving a structure prior, m was estimated by setting the gradients of magnitude image
greater than a certain threshold to 0 and to 1 otherwise .
(1) Form a 3D complex image dataset with the real component filled with the magnitude image
data and the imaginary component filled with zeroes.
Reconstructed images of the breast phantom with the tumor highlighted, (a) magnitude image
, (b) phase image.
First, the sinc interpolation applied to the magnitude image
is only an approximation of the complex k-space VSI, due to the lack of phase information presented in the image data.
It has little influence on the magnitude image
, but it may destroy the joint probability density function (PDF) of magnitude and phase in the interferometric image as explained in Section 2.