Dispersion artifacts

Figure 10.1 Mean extracted spectra from a cluster analysis performed on cervical tissue. The spectra were extracted from the three outermost clusters surrounding a gland that was devoid of tissue. The clusters represent, approximate distances of (A) 5 [xm, (B) lOjxmand (C)20 xm penetration into the surrounding stroma. Spectra (A) and (B) show varying degrees of die dispersion artifact while spectrum (C) is devoid of the artifact.

The wavenumber resolution was set at 6 cm-1 and 16 scans were coadded for each spectrum. UHCA was performed on the 1800-950 cm-1 region on second-derivative vector normalized spectra. The brown cluster and resultant mean extracted brown spectrum in Fig. 10.7(c) are representative of the dispersion artifact from... 

Diem, M. (2004) Correction of dispersion artifacts in IR microspectral data. SPEC2004 Shedding New Light on Disease Optical Diagnosis for the New Millenium, Third International Conference, 19-24 June, Rutgers University, Newark, NJ. 

In the neck, time of flight techniques are preferred over phase contrast techniques due to the longer scan times of phase contrast techniques needed to provide the same coverage and spatial resolution. 2D TOF MRA provides superior flow-related enhancement and allows coverage of the entire neck. Compared to 2D TOF MRA, 3D TOF MRA provides superior spatial resolution and is less susceptible to phase dispersion artifacts, but is more susceptible to saturation effects and cannot cover a large area. 3D TOF flight techniqnes are, therefore, used to delineate the carotid bifurcation only. 2D PC techniques are used to evaluate flow direction in the vertebral arteries when subclavian steal is... 

P. Bassan, H. J. Byrne, F. Bonnier, J. Lee, P. Dumas and P. Gardner, Resonant Mie scattering in infrared spectroscopy of biological materials understanding the dispersion artifact . Analyst, 2009, 134, 1586-1593. 

Fig. 4.27. Artifacts in energy-dispersive X-ray spectra. Occur renceof(a) escape and (b) sum peaks.

The sine-bell functions are attractive because, having only one adjustable parameter, they are simple to use. Moreover, they go to zero at the end of the time domain, which is important when zero-filling to avoid artifacts. Generally, the sine-bell squared and the pseudoecho window functions are the most suitable for eliminating dispersive tails in COSY spectra. 

In order to avoid flow artifacts it may be advisable to replace the spatial encoding pulses (right-hand box) by velocity compensated pulses such as shown in Figure 2.9.4(e) for phase encoding. The amplitude of the Hahn spin-echo is attenuated by hydrodynamic dispersion. Evaluation of the echo attenuation curve for fixed intervals but varying preparation gradients (left box) permits the allocation of a hydrodynamic dispersion coefficient to each voxel, so that maps of this parameter can be rendered. 

This EPMA line scan was analysed by wavelength dispersive spectroscopy, being part of a study by Horz and Kallfass of ornamental and ceremonial artifacts dated to approximately AD 50-300, recovered from the Royal Tombs of Sipan, Peru. 

Linke, R. and Schreiner, M. (2000). Energy dispersive X-ray fluorescence analysis and X-ray microanalysis of medieval silver coins - an analytical approach for non-destructive investigation of corroded metallic artifacts. Mikrochimica Acta 133 165-170. 

Transmission electron microscopy (TEM) can provide valuable information on particle size, shape, and structure, as well as on the presence of different types of colloidal structures within the dispersion. As a complication, however, all electron microscopic techniques applicable for solid lipid nanoparticles require more or less sophisticated specimen preparation procedures that may lead to artifacts. Considerable experience is often necessary to distinguish these artifacts from real structures and to decide whether the structures observed are representative of the sample. Moreover, most TEM techniques can give only a two-dimensional projection of the three-dimensional objects under investigation. Because it may be difficult to conclude the shape of the original object from electron micrographs, additional information derived from complementary characterization methods is often very helpful for the interpretation of electron microscopic data. 

The Van Deemter equation remained the established equation for describing the peak dispersion that took place in a packed column until about 1961. However, when experimental data that was measured at high linear mobile phase velocities was fitted to the Van Deemter equation it was found that there was often very poor agreement. In retrospect, this poor agreement between theory and experiment was probably due more to the presence of experimental artifacts, such as those caused by extra column dispersion, large detector sensor and detector electronic time constants etc. than the inadequacies of th Van Deemter equation. Nevertheless, it was this poor agreement between theory and experiment, that provoked a number of workers in the field to develop alternative HETP equations in the hope that a more exact relationship between HETP and linear mobile phase velocity could be obtained that would be compatible with experimental data. 

---