Radiography contrast

Sandborg, M. and G. Alm-Carlsson, Influence of x-ray energy spectrum, contrasting detail and detector on the signal-to-noise ratio (SNR) and detective quantum efficiency (DQE) in projection radiography. Phys. Med. Biol., 1992. 37(6) p. 1245-1263. 

Contrast Sensitivity For monitoring purposes, a step wedge is to be used that consists of the same material as the workpiece. In addition, IQIs according to EN 462-1 or EN 462-2 - DIN wire penetrameters or step-hole IQIs - can be applied to ensure a comparability with radiography. 

The specific advantage of this technique is its higher sensitivity than classical film radiography and the potential for automated image processing due to the digital read-out of the IP s. Former investigations have shown / / that the available IP s achieve the same contrast like NDT films with an IP type and scanner dependent unsharpness. 

It also requires two- sided aceess to the structural element in question. The degree of contrast between homogenius concrete and concrete with voids will not decrease linearly with increasing thickness, and the maximum practical thickness of concrete elements which can be studied for small voids using film radiography is of course limited, but sufficient for most civil engineering applications. 

There ate four main approaches to x-ray imaging contact radiography, scanning x-ray microscopy, holographic x-ray microscopy, and shadow projection x-ray microscopy. In the future, there will likely be phase-contrast imaging and photoelectron x-ray microscopy. 

Molecular and cellular processes were visualized by X-ray contrast agents long before the term molecular imaging became popular and even before the advent of early CT (Table 1). Because of the above-mentioned limitations in the sensitivity of contrast detection by X-ray radiography, the latter can only visualize high capacity transport mechanisms and the nonspecific uptake of particles by specialized cells. 

Soft, silvery metal whose isolation is difficult. Ytterbium fluoride is added to dental fillings (as X-ray contrast agent). Ytterbium is a constituent of rust-free special steels. Yb2Co13Fe3Mn holds the magnetic world record, but is too expensive for commercial purposes. The element is occasionally applied in nuclear medicine and radiography. It also activates phosphors that convert infrared rays into visible light. 

BaS04 used as contrast agent for radiography and MRI and in bone cements used for the fixation of joint prostheses, Ba inhibits K flux through potassium ion channels Radiation therapy for carcinomas... 

Practically all available iodinated extracellular X-ray contrast agents have been encapsulated into liposomes using different lipids and methods of preparation. Table 1 gives a short and intentionally incomplete overview of some of the approaches. The first liposomal contrast agent preparation that was tested in humans contained diatrizoate [48]. The injected dose was up to 0.5 ml kg k The preparation was effective even in plain radiography where lesions down to 0.8-1.0 cm could be detected in patients. However, adverse events such as fever and hyperthermia, which occurred in 30% of the patients, limited further use. We have incorporated iopromide into MLVs that were prepared from phosphatidyl choline (PC), cholesterol and stearic acid at a molar ratio of 4 5 1 using the ethanol-evaporation technique [44]. The liposomes can be stored freeze-dried and they are reconstituted before use by... 

The assignment of a lesion into one of these types is purely morphological and based on the anatomical location of the tumor or the best estimate of its epicenter for those with advanced disease. Classification can be performed easily based on a combination of contrast radiography, upper endoscopy, and CT (38). In a retrospective analysis of 74 patients with gastric cancer, the preoperative classification had a high correlation (95%) to the final classification based on the resected specimen (39). 

By contrast, the metals have so far found only limited application save for one important use in the field of nondestructive testing. With the proliferation of research reactors over the past decade, neutron radiography has become a practical tool in the aerospace, nuclear and engineering industries, yet without the availability of gadolinium and dysprosium in the form of thin foils, the technique would be severely restricted. 

At present only rare earth x-ray phosphors meet most of these characteristics. Rare earth phosphors are also useful for color contrast radiography. 

When X-rays interact with any kind of materials, absorption and phase shifts effects occur. Conventional X-ray radiography relies on the absorption properties of the sample. The image contrast is produced by a variation of density, a change in composition or thickness of the sample, and is based exclusively on the detection of an amplitude variation of X-rays transmitted through the sample itself. Information about the phase of X-rays is not considered. The main limitation of this technique is the poor intrinsic contrast in samples with low atomic number (i.e., the case of soft matter ) or in materials with low variation of absorption from point to point. 

Other NDT Methods. Radiography (x-ray) inspection can be used to detect voids or discontinuities in the adhesive bond. This method is more expensive and requires more skilled experience than ultrasonic methods. The adhesive must contain some metal powder or other suitable filler to create enough contrast to make defects visible. This method is applicable to honeycomb sandwich structures as well as metal and nonmetal joints. 

For soft human tissue that would be otherwise have too low a contrast to be resolved in conventional high-intensity planar X-ray radiography, a thorough study of X-ray absorbance as a function of tissue density and thickness allowed the development of hardware and software for computed axial tomography (CAT scanning) which performs a three-dimensional analysis of X-ray absorption at low intensities and convenient two-dimensional displays of resolved human tissue features. 

In contrast, the application of x-ray radiography to archaeological materials and other three-dimensional objects has not reached the same level of sophistication. The reasons seem obvious the more powerful... 

Oide S, Yamaguchi H, Niizu N, Takahashi S, Takashima K. [Transient neonatal hypothyroidism probably due to contrast media used in fetal radiography.] Horumon To Rinsho 1983 31(Suppl) 76-9. 

Acepromazine maleate is advocated for use in the treatment of esophageal obstruction but, aside from its sedative effects, there is no direct evidence that it promotes esophageal relaxation. In one report using barium contrast radiography, acepromazine appeared to cause mild segmental dilatations in the thoracic esophagus (King et al 1990). The duration of effect of acepromazine is 2 to 3h and it may be useful in the treatment of obstructions that do not resolve quickly. The dose rate is 0.02-0.04 mg/kg i.v. or i.m. 

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