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A '''medical contrast medium''' (or '''contrast agent''') is a [[Chemical substance|substance]] used to enhance the [[contrast]] of structures or fluids within the body in [[medical imaging]].<ref>{{DorlandsDict|nine/12901138|contrast agent}}</ref> It is commonly used to enhance the visibility of [[blood vessels]] and the [[gastrointestinal tract]].
#تحويل [[مادة تباين]]
{{ترجمة}}
==الأنواع==
Several types of contrast media are in use in medical imaging and they can roughly be classified based on the imaging modalities where they are used. Although other types exist, most common contrast agents work based on X-ray [[attenuation (electromagnetic radiation)|attenuation]] and magnetic resonance signal enhancement.
 
===أشعة إكس===
X-ray attenuation
{{main|Radiocontrast agent}}
[[Iodine]] and [[barium]] are the most common types of contrast medium for enhancing x-ray-based imaging methods. Various sorts of iodinated contrast media exist, with variations occurring between the [[osmolarity]], viscosity and absolute iodine content of different media. Non-ionic [[dimer (chemistry)|dimers]] are favored for their low osmolarity and toxicity, but have a correspondingly higher price attached to their use.<ref name=AP>Thomson, K; Varma, D (2010). "Safe use of radiographic contrast media". ''Australian Prescriber'', 33:19-22. Available at http://www.australianprescriber.com/magazine/33/1/19/22/</ref>
 
===تحسين إشارة الرنين المغناطيسي===
MR signal enhancing
{{main |MRI contrast agent}}
This would include [[gadolinium]] for use in [[magnetic resonance imaging]] as a [[MRI contrast agent]]. In the 3+ oxidation state the metal has 7 unpaired f electrons. This causes water around the contrast agent to relax quickly, enhancing the quality of the MRI scan.
 
===تشتت الأمواج الفوق الصوتية وانحراف التوتر===
Ultrasound scattering and frequency shift
{{main|Contrast-enhanced ultrasound}}
Microbubble contrast agents are used to aid the [[Medical ultrasonography|sonographic]] examination, specifically [[Echocardiography|echocardiogram]]s, for the detection of a [[cardiac shunt]]. These bubbles are composed of agitated saline solution, most of which are too large to pass through the lung capillaries. Therefore, the only ones that reach the left side of the heart pass through an abnormal connection between the two sides of the heart, a so-called right-to-left shunt. In addition, pharmaceutically prepared microbubbles are composed of tiny amounts of [[nitrogen]] or [[perfluorocarbon]]s strengthened and supported by a protein, lipid, or polymer shell. These are small enough to pass through the capillaries and are used to increase the contrast in the left ventricle, improving the visualization of its walls. The drop in density on the interface between the gas in the bubble and the surrounding liquid strongly scatters and reflects the ultrasound back to the probe. This process of [[backscatter]]ing gives the liquid with these bubbles a high signal, which can be seen in the resulting image.
 
== الآثار الضارة ==
While modern contrast media are generally safe to use,<ref name=AP/> medical conditions can be caused by the administration of various contrast media.  Reactions can range from minor to severe, sometimes resulting in death<ref>{{Cite journal  | last = Caro  | first = J. Jaime  | coauthors = Evelinda Trindade, Maurice McGregor  | title = The Risks of Death and of Severe Nonfatal Reactions with High- vs Low Osmolarity Contrast Media: A Meta-analysis  | journal = American Journal of Roentgenology  | volume = 156  | issue = 4  | pages = 825–832  | publisher = American Roentgen Ray Society  | year = 1991  | url = http://www.ajronline.org/cgi/content/abstract/156/4/825  | pmid = 1825900}}</ref> with death being about 0.9 per 100,000 cases. To better understand the reactions and to efficiently manage patients at risk, it is useful to classify them.<ref>Böhm I, Heverhagen JT, Klose KJ. Classification of acute and deleayed contrast media-induced reactions: proposal of a three-step system. Contrast Media & Molecular Imaging 2012;7(6):537-41 url=http://onlinelibrary.wiley.com/doi/10.1002/cmmi.1475/pdf</ref> Risk factors for developing severe reactions include strong allergies, bronchial asthma, cardiac disease and beta-blocker use.<ref name=Brockow2005>{{Cite journal  | last = Brockow  | first = K.  | coauthors = et al.  | title = Management of hypersensitivity reactions to iodinated contrast media  | journal = Allergy  | volume = 60  | issue = 2  | pages = 150–158  | publisher = European Journal of Allergy & Clinical Immunology  | date = 11 Jan 2005  | url = http://www3.interscience.wiley.com/journal/118649563/abstract  | pmid = 15647034  | doi = 10.1111/j.1398-9995.2005.00745.x}}</ref><ref>Boehm I. Contrast media and patients at risk: asthma. Acta Radiologica 2009; 50(3): 348</ref>
 
A common misconception that even exists among healthcare professionals is that an allergy to contrast media is related to an allergy to seafood (usually shellfish) because both share iodine in common, implicating iodine as a source.<ref>{{Cite journal  | last = Coakley  | first = Fergus  | coauthors = David M. Panicek  | title = Iodine Allergy: An Oyster Without a Pearl?  | journal = American Journal of Roentology  | volume = 169  | issue = 4  | pages = 951–952  | publisher = AJR  | date = October 1997  | url = http://www.scopus.com/record/display.url?eid=2-s2.0-0031253782&view=basic&origin=inward&txGid=sahILGe6CUTnUXnL0epp4EJ%3a9}}
</ref><ref>http://www.wdxcyber.com/ngen22.htm</ref> Numerous studies have shown that although iodine is common in contrast media, iodine is not the cause of allergic reactions to contrast media and instead the more likely culprit are the inert ingredients and the patient's past history of having other strong allergic reactions.<ref>{{Cite journal  | last = Boehm  | first = Ingrid  | title = Seafood Allergy and Radiocontrast Media: Are Physicians Propagating a Myth?  | journal = The American Journal of Medicine  | volume = 121  | issue = 8  | pages = e19  | publisher = Elsevier  | date = August 2008  | url = http://linkinghub.elsevier.com/retrieve/pii/S0002934308003537  | pmid = 18691465  | doi = 10.1016/j.amjmed.2008.03.035}}</ref> One important distinction is that allergic effects are by definition immunoglobulin E related histamine storms and studies have shown that contrast media cause no such reaction in vivo <ref>{{Cite journal  | last = Carr  | first = Denis H.  | coauthors = Archi C. Walker  | title = Contrast Media Reactions: experimental evidence against the allergy theory  | journal = British Journal of Radiology  | volume = 57  | issue = 678  | pages = 469–473  | publisher = British Institute of Radiology  | year = 1984  | pmid = 6722447  | url = http://bjr.birjournals.org/cgi/content/abstract/57/678/469  | doi = 10.1259/0007-1285-57-678-46}}</ref> thereby refuting the possibility that contrast media or the iodine in it is likely to be an allergen. Although it may seem contradictory, the few rare cases of contrast medium mediated IgE are exceedingly rare compared to all adverse reactions and when they happen, are often because the patient already has multiple risk factors that suggest the patient has other allergy related problems.<ref name=Brockow2005/>
 
Historically, contrast media was sometimes highly dangerous but these dangers were not well-understood during the development of the early types of contrast media, such as [[Thorotrast]].
 
==انظر ايضاً==
*[[iodinated contrast]]
*[[ipodate sodium]]
*[[Radiocontrast]]
*[[Medical imaging]]
*[[Radiology]]
 
== مصادر ==
{{reflist}}
* [http://en.wikipedia.org/wiki/Contrast_medium مواد ظليلة (مواد تباين) على wikipedia]
* [http://ar.wikipedia.org/wiki/%D9%85%D8%A7%D8%AF%D8%A9_%D8%AA%D8%A8%D8%A7%D9%8A%D9%86 مادة تباين / ويكيبيديا العربية]
{{Major drug groups}}
{{Contrast media}}
 
{{DEFAULTSORT:Contrast Medium}}
[[Category:Contrast agents]]

المراجعة الحالية بتاريخ 13:28، 14 ديسمبر 2012

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