Contrast medium 3244736 206900721 2008-04-20T15:54:03Z 189.6.180.226 /* References */ {{see also|Radiocontrast}} In a medical setting, a '''contrast medium''' is any [[substance]] that is used to enhance the visibility of structures or fluids within the body. An example of this is the use of a [[Radiopacity|radiopaque]] substance during an [[Medical radiography|x-ray exam]] to highlight features that would otherwise be less distinguishable from nearby tissue. Another example is the use of air bubbles during an [[Echocardiography|echocardiogram]] to search for a [[shunt]] in the [[heart]]. ==Summary== The contrast can either be ''positive'' or ''negative''. Positive contrast media has a higher [[attenuation (electromagnetic radiation)|attenuation]] density than the surrounding tissue. This means that the contrast looks more opaque than the surrounding tissue when seen on an x-ray. Negative contrast media has a lower attenuation density than the surrounding tissue. This means that the contrast looks less opaque than the body. Negative contrast is only found as a gas. Positive contrast is a substance with a high atomic number, but is also non-toxic. Contrast can be used to produce images of almost any hollow structure in the body. ==Types of Positive Contrast Medium== *Iodine Based *Non Iodine Based *Other ===Iodine Based Contrast Media=== Iodine based contrast media such as [[urografin]] or [[Omnipaque]] is used most commonly in radiology, due to its relatively harmless interaction with the body. It is primarily used to visualise vessels, but can also be used for tests of the urinary tract, uterus and fallopian tubes. {| class="wikitable sortable" border="1" cellpadding="5" cellspacing="0" align="center" |+'''Commonly used iodinated contrast agents''' |- ! style="background:#ffdead;" | Compound ! style="background:#ffdead;" | Name ! style="background:#ffdead;" | Type ! style="background:#ffdead;" | Iodine Content ! style="background:#ffdead;" | Osmolality ! style="background:#ffdead;" | Level |- | Ionic | [[Diatrizoate]] (Hypaque 50) | Ionic Monomer | 300 | 1550 | High Osmolar |- | Ionic | [[Metrizoate]] (Isopaque Coronar 370) | Ionic | 370 | 2100 | High Osmolar |- | Ionic | [[Ioxaglate]] (Hexabrix) | Ionic dimer | 320 | 580 | Low Osmolar |- | Non-Ionic | [[Iopamidol]] (Isovue 370) | Non-ionic monomer | 370 | 796 | Low Osmolar |- | Non-Ionic | [[Iohexol]] (Omnipaque 350) | Non-ionic | 350 | 884 | Low Osmolar |- | Non-Ionic | [[Ioxilan]] (Oxilan) | Non-ionic | | | Low Osmolar |- | Non-Ionic | [[Iopromide]] | Non-ionic | | | Low Osmolar |- | Non-Ionic | [[Iodixanol]] (Visipaque 320) | Non-ionic dimer | 320 | 290 | Iso Osmolar |} ===Non Iodine Based Contrast Media=== These often appear in the form of [[barium sulfate]]. Barium is mainly used in the imaging of the digestion system. ===Other=== This would include [[gadolinium]] for use in [[magnetic resonance imaging]] as a [[MRI contrast agent|contrast agent]]. ==Types of Negative Contrast== Negative contrast always occurs in a gas, usually as one of the following: *Air *Carbon dioxide *Oxygen ==Clinical Applications== Examples of the use of '''positive contrast medium''' are as follows: ===Iodine Base Contrast Media=== [[Image:Cerebral Angiogram Lateral.jpg|thumb|200px|right|Example of Iodine based contrast in Cerebral Angiography]] [[Image:DCBE.jpg|thumb|200px|right|Example of a DCBE]] *Angiography (''Arterial Investigations'') *Venography (''Venous Investigations'') *MCUG (''Micturating Cysto Urography'') *HSG (''Hysterosalpinogram'') *IVU (''Intravenous Urography'') ===Non Iodine Based Contrast Madia (Barium Studies)=== *Barium Enema (''Large Bowel Investigation'') *Barium Swallow (''Oesophagael Investigation'') *Barium Meal (''Stomach Investigation'' ) *Barium Follow Through (''Stomach and Small Bowel Investigation'') ===Other=== [[Gadolinium]], or ''Gad'' for short, is used as a component of [[MRI contrast agent]]s, in the 3+ oxidation state the metal and has 7 unpaired f electrons. This causes water around the contrast agent to relax quickly, enhancing the quality of the MRI scan. ===Negative Contrast Media=== Examples of the use of '''negative contrast medium''' are as follows: *DCBE (''Double Contrast Barium Enema'') *Double Contrast Barium Meal *CT Pneumocolon / Virtual Colonoscopy *the use of air bubbles to aid the [[Medical ultrasonography|sonographic]] detection of a [[cardiac shunt]] ==Allergy Reactions== Although rare, it is possible to be allergic to contrast media. Reactions can range from minor to severe, in the worst case scenario, resulting in death. '''Mild''' (no treatment necessary) *Hot flush *Vomiting '''Moderate''' (treatment necessary, but no intensive care) *[[Urticaria]] (hives) *Slight wheezing ([[bronchospasm]]) '''Severe''' (life-threatening, intensive care necessary) *Respiratory arrest *Cardiac arrest Contrast media is never given to a patient unless a doctor is present to assist should an allergic reaction occur. Patients are usually screened before being given contrast, by means of a series of questions. These typically include an allergy history and a history of any asthma and diabetes. ==Drug Interactions== It has been recommended[http://www.amershamhealth-us.com/medpro/clinref/glucophage.html] that [[metformin]], an oral antidiabetic agent, be stopped for 48 hours following the [[intravascular]] administration of contrast media and that the use of metformin not be resumed until renal function has been shown to be normal. The reasoning is that if the contrast medium causes kidney failure (as happens rarely) and the person continues to take metformin (which is normally excreted by the kidneys), there may be a toxic accumulation of metformin, increasing the risk of [[lactic acidosis]], a dangerous complication. However, guidelines published by the Royal College of Radiologists suggest this is not as important for patients who receive <100mls of contrast media and have [[creatinine|normal renal function]]. If renal impairment is found before administration of the contrast, metformin should be stopped 48 hours before and after the procedure.<ref>Thomsen HS, Morcos SK, and members of the Contrast Media Safety Committee of the European Society of Urogenital Radiology. Contrast media and Metformin. Guidelines to distinguish the risk of lactic acidosis in non-insulin dependent diabetics after administration of contrast media.European Radiology, 1999; 9: 738-740.</ref>. ==Toxicity== :See [[Radiocontrast#Contrast-induced_nephropathy|Contrast-induced nephropathy]] [[Nephrotoxicity]] (toxicity to the kidneys) is a major consideration for clinicians when requesting tests which use an iodine-based contrast media. Patients whose renal function is impaired (usually with a creatinine >120 micromol/litre) should only have contrast media if absolutely necessary. In these circumstances, a special form of contrast media, which is 'kinder' to the kidneys, can be given. ==See also== *[[Medical imaging]] *[[Radiology]] *[[Radiocontrast]] ==References== <references/> *[[Dorland's Illustrated Medical Dictionary]] (Twenty-sixth Edition) (ISBN 0-7216-1645-3) [[Category:Medical imaging]] [[Category:Radiography]] [[zh:顯影劑]] [[ja:造影剤]] [[de:Kontrastmittel]] [[nn:Kontrastmiddel]] [[pt:Meio de contraste]]