1. A method for determining the complex scattering function of a portion of a sample under analysis, the method comprising: (a) providing a magnitude spectrum of a complex spatial Fourier transform of a complex intermediate function, the complex intermediate function dependent on the complex scattering function of the portion of the sample under analysis, the magnitude spectrum obtained from power spectrum data of frequency-domain optical coherence tomography of the portion of the sample under analysis; (b) providing an estimated phase term of the complex spatial Fourier transform; (c) multiplying the magnitude spectrum and the estimated phase term together to generate an estimated complex spatial Fourier transform; (d) calculating an inverse Fourier transform of the estimated complex spatial Fourier transform, wherein the inverse Fourier transform of the estimated complex spatial Fourier transform is a spatial function; and (e) calculating an estimated intermediate function by applying at least one constraint to the inverse Fourier transform of the estimated complex spatial Fourier transform.