Resolution and Contrast

In all microscopy a primary concern is the spatial resolution that can be obtained. If the details are points, the resolution may be specified as point-to-point resolution. An object with regularly repeating details such as a set of lines will give a different value for resolution. This is important as some convenient test objects are ruled lines in optics, and lattice fringes (sheets of atoms) in TEM. Near the resolution limit, images of two objects will overlap and this will reduce contrast. A precise measure of resolution requires a quantitative test to determine if the detail can be distinguished, and so there is a need for a quantitative definition of contrast. The contrast of a feature is generally defined as 

In other cases, a logarithmic definition is more useful [6, 39]  

This means that great care is required in comparing results from different sources. The most complete method of defining resolution is to measure the ratio (contrast in the image)/ (contrast in the object) as a function of detail separation. This is the modulation transfer function (MTF), also called the contrast transfer function (CTF), which describes how the modulation or contrast in the object is transferred to the image. Qearly, when MTF falls to some very smaU value, no object detail is reproduced in the image. 

Four factors may limit the resolution of an image, and these are  

The diffraction limit depends on the wavelength of the radiation and the angular acceptance of the objective. The diffracted beams caused by a periodicity d come off at angles given by sin = A/d or greater. Therefore the lens must accept a semi-angle a j tor 

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The inspection class SB covers requirements beyond serial inspection for higher geometric resolution and contrast sensitivity (acc.EN 462). 

MRI has become the preferred modality for medical and diagnostic imaging due to the superior resolution and contrast in the images. MRI has several advantages over X-ray CT, in that MRI does not result in any accumulated ionizing radiation dose to the subject, and it can detect spinal lesions, such as multiple sclerosis, that would otherwise go undetected in X-ray CT (see Appendix Brief history of medical imaging, and refs [1-9]). However, MRI does pose a minimal risk to the subject in several ways. 

What is dark-field microscopy How does it compare in terms of resolution and contrast with conventional optical microscopy ... 

Scanning force microscopes can be operated in many ways measuring different interactions between the probe tip and sample and using different types of detection schemes. Development of new modes is driven by the wish of the experimentalist (i) to discriminate the different contributions to the net force, such as adhesion, elasticity and viscosity, (ii) to enhance the resolution and contrast of the microscope, and (iii) to diminish distortion of the tip and sample during scanning. 

As methodologies in FISH and mFISH on the fluorescent microscope evolve, so must the software and hardware used to unravel the information contained in the specimen. A proper combination of filters, dyes, imaging hardware, and software is desirous for obtaining the resolution and contrast necessary for accurate image capture and analysis. 

Besides the most important area of surface coatings, the use of photopolymers as photoresists in the manufacture of printed circuits is well established. Photoimaging with aryldiazonium salt photoinitiators and multifunctional cresol-novolac epoxides was first described by Schlesinger Crivello has mentioned several new photoresists based on the photopolymerization of epoxides with onium initiators Meier and Zweifel have shown that iron arene salts in combination with multifunctional cresol-novolac epoxides yield photoresists with high resolution and contrast. Dual functional epoxides (cf. Sect. 5) containing chalcone groups as light-sensitive units have been described as suitable photoresists especially... 

Acrylate resists such as polymethylmethacrylate (PMMA) have been used extensively in electron beam lithography because of their excellent resolution and contrast, despite their limited dry etch resistance and low sensitivity (1). Copolymers of PMMA, containing chemical groups more sensitive to radiation induced degradation, have also been studied and have shown up to a four-fold improvement in sensitivity (2). One approach has been to form a crosslinked gel, in-situ on the wafer, which contains radiation sensitive crosslinks and leads to improved sensitivity and improved contrast during development (3-7). 

Poly(methylmethacrylate), (PMMA), is one resist which is especially favored by researchers due to its high resolution and contrast. Linewidths as small as 100 A have been produced with an extremely high dose of x-rays (10 J/cm ) using PMMA. However, even PMMA s normal sensitivity of 600-1000 mJ/cnr is too slow for commercial use. There have been many attempts to improve the sensitivity of PMMA to electron beam irradiation mainly by copolymerization (8). In the current paper, we describe an alternative approach whereby a sensitive polymer is physically blended with PMMA to increase its sensitivity and yet maintain the good film qualities associated with PMMA as a positive x-ray resist. 

Any comparison of the imaging characteristics of STEM and CTEM must, then, invoke the principle of reciprocity, considered by numerous authors. Put most simply, reciprocity between the reversed paths in Figure 2 for STEM and CTEM implies that, for identical geometrical conditions, the resolution and contrast in the... 

Adjust the field diaphragm for maximum contrast and the aperture diaphragm for maximum resolution and contrast and... 

The principles of spatial resolution and contrast in NMR imaging have been presented in this chapter. An overview of selected applications of NMR to investigations of fluid systems, technical elastomers and rigid polymers has been given. The examples chosen demonstrate the potential of NMR for measurement of macroscopic properties of polymer materials. The importance of developments of NMR methods and equipment for materials science applications was underlined by example of the NMR MOUSE. 

Figure 2 illustrates the phase and amplitude resolution of our device. Shown in this figure is a spectrum collected for a shaped pulse generated by a series of 3-ns acoustic waves separated by 665 ns, shown in Fig. 2b. Each wave deflects a particular frequency in the mid-IR pulse spectrum to create a comb of frequencies. The resulting peaks each have an fwhm of 5 nm and are separated by 63 nm, demonstrating the high resolution and contrast ratio of the pulse shaper. Considering that the 3-ns duration of each acoustic pulse is smaller than...

The use of PMMA as a resist is favored by researchers because of its high resolution and contrast [Jubinsky et al., 1986]. However, its sensitivity is too low for commercial use. Jubinsky et al. [1986] describe an approach to improve its sensitivity, by blending it with a radiation-sensitive polymer, CO (poly(epichlorhydrin). Hydrin ) (Table 11.9). Three blends were made by dissolving CO and PMMA in tetrahydrofuran (CO/PMMA 20/80, 33/67 and 50/50), in the... 

Above about 0.5 GHz, Brillouin scattering provides an elegant technique of measuring phonon mean free paths (which are inversely proportional to the sound attenuation coefficient) by evaluating the width of the Brillouin lines [53]. However, as a result of finite spectrometer resolution and contrast, this method is limited to aerogel densities above 180 kg/m. ... 

Wintermark, M., et al., Dynamic perfusion CT optimizing the temporal resolution and contrast volume for calculation of perfusion CT parameters in stroke patients. AJNR Am J Neuroradiol, 2004. 25(5) p. 720-9. 

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