Image Artifacts

While SPM offers unique advantages for surface measurement in terms of simplicity and high resolution, it also has its unique problems of image artifacts caused by near-field interactions between tip and sample. The artifacts in imaging may originate from the tip, the scanner, vibrations and/or image processing. Typical artifacts as introduced from several sources are briefly described in this section. 

---

Fourth, in the vertical and horizontal directions, the stiffness should be very different. When the AFM is operated in the repulsive-force mode, frictional forces can cause appreciable image artifacts. Choosing an appropriate geometry for the shape of the lever can yield substantial lateral stiffness, thus minimizing the disturbing artifacts. 

This item seems to be related to the perception of pre-echo effects (test subjects who are very sensitive for pre-echoes in some cases are known to be very insensitive to imaging artifacts). Not much is known here, so this is a topic for future research. 

Figure 3.16 Example of an imaging artifact. Left object consisting of an opaque specimen except for a 12 p,m diameter circular aperture. Right calculated transmission image for a single (nonconfocal) Schwarzschild objective with NA = 0.65 and for k = 6 p,m. Note the dark patch in the center, suggesting the presence of absorbing material inside the hole.

Figure 3.17 Imaging artifact for a specimen consisting of a thin uniform layer except for a 12 pm diameter hole (aperture), using a nonconfocal 32 x Schwarzschild objective (NA = 0.65) and X = 6 pm. Solid line calculated absorption profile through the diameter of the hole. Solid circles measured absorption profile for an actual specimen. Note the poor absorption contrast (—50%) and bump at the holes center (15 pm location).

Sureshbabu W, Mawlawi O (2005). PET/CT imaging artifacts. J Nucl Med Technol 33 156... 

A potential problem with light microscopy, especially with high intensity mercury vapor lamps (for blue-violet incident light), is localized sample heating however, for suspensions this phenomenon is generally not as important in creating image artifacts as interactions with the sample holder. 

Initiatives to share artifacts between centers should be initiated. Databases of image artifacts would not only improve tbe knowledge,but also open the door toward an automated tracking or analysis. 

---