**3. The Circular-Shape Fourier Transform (CFT)**

This section describes the circular-shape Fourier transform (CFT). We begin with the sampling grid in the Fourier domain, including the Cartesian coordinates (see Figure 3a) for classical Fourier transform and the pseudo-polar grid in [5] (see Figure 3b). This grid samples points of equally spaced long rays but not equally angles. In order to have a circular structure, the sampling grid in concentric circles (see Figure 3c) is designed, which has equally arc and angle in each circle. This type of sampling is consistent with the distribution of images in the frequency domain.

**Figure 3.** Three different grids.
