Complex observation in electron microscopy: III. Inverse theory of observation-scheme dependent information transfer

A comparative approach to investigate what is renovated in transmission electron microscopy (TEM) with the recently proposed complex observation is reported. To make the comparison quantitative among various TEM schemes proposed to date, a novel TEM index, information transfer reliability (ITR), was introduced based on a linear inverse theory originally developed to characterize measurement models. ITRs regarding to four different observation schemes (two unreplaceable schemes: bright-field (conventional) and Zernike phase-contrast, and two derived schemes: defocus series based on conventional and complex obtained from a combination of conventional and Zernike phase-contrast) were calculated for the images respectively obtained with computer simulation for a protein, a high potential sulfur protein. Recognition of the 0.5 nm-diameter prosthetic group, an iron-sulfur cluster, included in the protein was used as a criterion for good-quality images. Based on the argument on the relation between the recognizability by our image perception and the TEM index ITR calculated for the same image, superiority in the observation scheme was quantitatively confirmed for the complex observation and its single experimental version, phase-contrast.