Biomedical Imaging

$\Delta \lambda /a^2\le 1.\left(6.99\right)$

In other words, the Fresnel number (defined for a single pixel and the object thickness) must be larger than 1 for the projection approximation to hold. If Δ ≥ a2/λ, one can resort to multislice approaches, with iterative steps of projection and propagation advancing through the object. In these iterations propagation is treated as in free space. The above validity criterion for the projection approximation does not explicitly depend on the refractive index. This is in contrast to the expectation that weakly scattering objects should be more benevolent with respect to neglecting diffraction in the object.

Born and Rytov approximation

This raises the interesting question, by which approach beyond the ...