One approach involves measurements along different rotated directions in phase space. For each direction θ θ , one can find a probability distribution w ( q , θ θ ) for the probability density of measurements in the θ θ direction of phase space yielding the value q . Using an inverse Radon transformation (the filtered back projection) on w ( q , θ θ ) leads to the Wigner function, W ( x , p ) , which can be converted by an inverse Fourier transform into the density matrix for the state in any basis. A similar technique is often used in medical tomography.