Required dose and tolerable dose for 3-D imaging using x-rays and electrons. The dashed line is the x-ray dose required for three-dimensional imaging of a protein (ρ = 1.35 g/cm3) as a function of the voxel dimension δ, according to . The solid line is the required electron dose calculated from Equation 2, taking λ
i = 3 and E
m = 35 eV. The dotted line represents the maximum tolerable dose, as determined by measurements by x-ray and electron diffraction measurements (round and triangular data points, respectively). For 3-D single-particle imaging, the best resolution corresponds to the intersection of the dotted line with the dashed line (for x-rays) or the solid line (for electrons).