Contrast media

Extravasation of barium sulfate iato the peritoneal cavity through a perforated GI tract can produce serious adverse reactions. When a perforation is suspected, the use of a water-soluble iodinated contrast medium is iadicated. In this case, oral or rectal administration of sodium or meglumine-sodium salts of diatrizoic acid (6) and oral use ofiohexol (11) are the preferred procedures. 

Other imaging techniques such as magnetic resonance and ultrasound have opened up avenues of tremendous potential for contrast medium enhancement (123). Ultrasound contrast media developments have centered around encapsulated air micro-bubbles. Magnetic resonance contrast agents iavolve metal—ligand complexes and have evolved from ionic to nonionic species, much as radiopaques have. 

Because of its extreme insolubiUty, barium sulfate is not toxic the usual antidote for poisonous barium compounds is to convert them to barium sulfate by administering sodium or magnesium sulfate. In medicine, barium sulfate is widely used as an x-ray contrast medium (see Imaging TECHNOLOGY X-RAY technology). It is also used in photographic papers, filler for plastics, and in concrete as a radiation shield. Commercially, barium sulfate is sold both as natural barite ore and as a precipitated product. Blanc fixe is also used in making white sidewall mbber tires or in other mbber appHcations. 

Target Contrast medium Commercial product or experimental Biological mechanism Reference... 

The mechanisms that are most likely to result in sufficient specificity and contrast medium concentration involve complicated multiple step reactions. 

The dioxolanones 33 <95JAP07291959> and 34 <95JAP07285960> are both reported to be useful as solvents, while 35 has been used as an X-ray contrast medium <96MIP19487>. Carboxydioxolanes such as 36 are useful for controlled release of volatile aldehyde pheromones <96JCR(S)274> and pharmaceutically active amines R2NH can be administered in... 

Immediate hypersensitivity reactions to RCM are associated with histamine release from basophils and mast cells [27], and extensive mast cell activation in vivo associated with clinical symptoms has been demonstrated by Earoche et al. [31]. Patients with hypersensitivity reactions after contrast medium exposure had increased plasma levels of both histamine and tryptase, and levels correlated with severity. Also other investigators have reported high levels of tryptase in connection with severe or fatal reactions [21, 33]. 

Previous reactors are at high risk for a new reaction. In many cases reported, re-administration of the culprit contrast medium to patients with a previous non-immediate exanthema resulted in a repeat reaction [1]. In some (but not all) cases, a more severe reaction with subsequent RCM exposure has been described. After provocation tests, a re-appearance of the exanthemas after intravenous administration of the culprit contrast medium has been reported in patients with previous contrast medium-induced eruptions [1]. 

Numerous positive delayed skin tests in patients with contrast medium-induced non-immediate skin reactions have been reported when the patients were tested with the culprit contrast medium [summarized in 1]. In a large European multicenter study, 37% of patients with non-immediate reactions were positive in delayed IDEs and/or patch tests [13]. The majority of the patients also reacted to the culprit contrast medium and also to other, structurally similar RCM. Notably, in more than 30% of those skin test-positive patients a RCM had been administered for the first time. Thus, there is a lack of a sensitization phase. Again it may be hypothesized that these previously non-exposed patients may have already been sensitized. Different patterns of RCM cross-reactivity indicate that several chemical entities could be involved. No positive skin tests have been obtained with other contrast medium excipients, such as ethylenediaminetetraacetic acid (EDTA), and only rarely patients have been found to react to inorganic iodide. 

Christiansen C, Dreborg S. Pichler WJ. Ekeli H Macular exanthema appearing 5 days after X-ray contrast medium administration. Eur Radiol 2002 12(suppl 3) S94-S97. 

Courvoisier S. Bircher AJ Delayed-type hypersensitivity to a nonionic, radiopaque contrast medium. Allergy 1998 53 1221-1224. 

In a different way, metallic-core nanoparticles [346-349] (prepared cf. Section 3.10) equipped with biocompatible coats such as L-cysteine or dextrane may be exploited for highly efficient and cell-specific cancer cell targeting, i.e., for improving diagnosis and therapy of human cancer. In a recent proof-of-principle experiment an unexpectedly low toxicity of the L-cysteine-covered cobalt nanoparticles was demonstrated [433] For diagnostic purposes, it is expected to use the advantageous magnetic properties of the metallic-core nanoparticles to obtain a contrast medium for MRI with considerably increased sensitivity, capable to detect micro-metastases in the environment of healthy tissues [434 37]. 

Penetration without perfusion failure of contrast medium to move out of the area of occlusion... 

Partial perfusion passage of contrast medium through obstruction but at a slow rate of clearance... 

Complete perfusion prompt antegrade flow distal to the obstruction and adequate clearance of contrast medium... 

Barium enema A diagnostic test using x-ray examination to view the lower gastrointestinal tract (colon and rectum) after oral ingestion of barium sulfate, a chalky liquid contrast medium. 

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