Statistical analysis of low-dose reconstruction of weak phase-amplitude objects from two defocused images - 2

The phase problem in low-dose electron microscopy of weak (biological) objects is investigated. To reduce the radiationdamage the electron dose has to be a minimum. The amplitudeand phase components of the object wave functions are estimatedd from the number of electrons arriving in cells in the image plane and are treated as stochastic quantities. The authors derive their probability densities. The estimation of the aplitude part of the object wave function presents no particular problems, the analysis of the phase component is more complicated because its low-frequency components are very weakly transmitted (depending on the dose). A filter process is introduced in order to eliminate the noise from these components. An explicit relation is derived between the variances of the estimates of the phase and amplitude components and the electron dose, providing a quantitative basis for low-dose electron microscopy of non-periodic objects.