A method determines the complex scattering function of a portion of a sample under analysis. The method includes providing a magnitude spectrum of a complex spatial Fourier transform of a complex intermediate function. The complex intermediate function is dependent on the complex scattering function of the sample. The magnitude spectrum is obtained from power spectrum data of frequency-domain optical coherence tomography of the sample. The method further includes providing an estimated phase term of the complex spatial Fourier transform. The method further includes multiplying the magnitude spectrum and the estimated phase term together to generate an estimated complex spatial Fourier transform. The method further includes calculating an inverse Fourier transform of the estimated complex spatial Fourier transform. The method further includes calculating an estimated intermediate function by applying at least one constraint to the inverse Fourier transform of the estimated complex spatial Fourier transform.