|k is assigned, whose direction indicates the direction of change and whose length indicates the density of stripes as shown to the right. By applying gradients, we “draw” patterns in the patient, one by one, in a predetermined order specific for the chosen sequence. All directions of stripes and all densities of stripes are drawn up until a certain limit. As said, the returned radio wave signal depends on the similarity between object and pattern and it is registered as a function of k as shown in Fig 4.9.
Fig 4.9: k-space
The voltage signal obtained at different phase encoding and frequency encoding steps are arranged in a space called ‘k-space’ and the image is calculated by adding patterns together that are weighted by the measured MR-signal. The calculation of fast fourier transform of the k-space for example can provide us with the image as shown in Fig 4.10.
Fig 4.10: k-space and corresponding image