One approach involves measurements along different rotated directions in phase space. For each direction formula_30, one can find a probability distribution formula_31 for the probability density of measurements in the formula_30 direction of phase space yielding the value formula_33. Using an inverse Radon transformation (the filtered back projection) on formula_31 leads to the Wigner function, formula_35, 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.