Use of a mass-thickness marker to estimate systematic errors and statistical noise in the detection of phosphorus by electron spectroscopic imaging.
The element signal obtained from electron-energy-filtered micrographs depends on the systematic error in calculating the background and on the noise in the background-corrected image. Both systematic error and statistical fluctuation of the background can be assessed experimentally with a specimen that combines the element-containing feature with a mass-thickness marker. The approach is described for the mapping of phosphorus in turnip yellow mosaic viruses prepared on a supporting carbon film of variable thickness. The thickness modulations are produced by the additional deposition of heat-evaporated carbon through a second grid used as a mask. The three-window power-law method and the two-window difference method are compared. With the three-window power-law method, the mass-thickness modulations of the marker are still visible in the map, indicating a systematic error for the calculated background. In addition, the intensity profile over the area of the thick carbon film is broader than in the map corrected by the two-window method, indicating a higher level of noise. With the two-window difference method, mass-thickness contrast was practically eliminated due to an improved protocol that uses the mass-thickness marker to calculate the scaling factor: instead of scaling the grey-level of a single background feature, the pre-edge image is scaled to the contrast of the marker area in the image acquired at the element-specific energy loss.
Richter
K
K
German Cancer Research Centre (DKFZ), Biomedical Structure Analysis Group, Heidelberg, Germany.
Haking
A
A
Troester
H
H
Spiess
E
E
Spring
H
H
Probst
W
W
Schultz
P
P
Witz
J
J
Trendelenburg
M
M
D004577:Electron Probe Microanalysis / Q000379:methods*; D016591:Histocytological Preparation Techniques; D010758:Phosphorus / Q000032:analysis*; D017806:Tymovirus / Q000737:chemistry* / Q000648:ultrastructure
D010758:Phosphorus