Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
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 radiopaque substance during an 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 echocardiogram to search for a shunt in the heart.
The contrast can either be positive or negative. Positive contrast media has a higher 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
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.
|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||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. Technetium, specifically isotope 99, is also used.
This would include gadolinium for use in magnetic resonance imaging as a contrast agent.
Types of Negative Contrast
Negative contrast always occurs in a gas, usually as one of the following:
- Carbon dioxide
Examples of the use of positive contrast medium are as follows:
Iodine Base Contrast Media
- 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)
Gadolinium, or Gad for short, is used as a component of MRI contrast agents, 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 sonographic detection of a cardiac shunt
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
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.
ACCF/AHA Guidelines for Anaphylactoid Reactions
"1. Patients with prior evidence of an anaphylactoid reaction to contrast media should receive appropriate steroid and antihistamine prophylaxis before repeat contrast administration. (Level of Evidence: B)"
|Class III (No Benefit)|
"1. In patients with a prior history of allergic reactions to shellfish or seafood, anaphylactoid prophylaxis for contrast reaction is not beneficial.(Level of Evidence: C)"
It has been recommended 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 normal renal function. If renal impairment is found before administration of the contrast, metformin should be stopped 48 hours before and after the procedure..
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) 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.
- ↑ Levine GN, Bates ER, Blankenship JC, Bailey SR, Bittl JA, Cercek B, Chambers CE, Ellis SG, Guyton RA, Hollenberg SM, Khot UN, Lange RA, Mauri L, Mehran R, Moussa ID, Mukherjee D, Nallamothu BK, Ting HH (2011). "2011 ACCF/AHA/SCAI Guideline for Percutaneous Coronary Intervention: Executive Summary A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Society for Cardiovascular Angiography and Interventions" (PDF). Journal of the American College of Cardiology. 58 (24): 2550–83. doi:10.1016/j.jacc.2011.08.006. PMID 22070837. Retrieved 2011-12-08. Text "PDF" ignored (help); Unknown parameter
- ↑ Klein LW, Sheldon MW, Brinker J, Mixon TA, Skelding K, Strunk AO, Tommaso CL, Weiner B, Bailey SR, Uretsky B, Kern M, Laskey W (2009). "The use of radiographic contrast media during PCI: a focused review: a position statement of the Society of Cardiovascular Angiography and Interventions". Catheterization and Cardiovascular Interventions : Official Journal of the Society for Cardiac Angiography & Interventions. 74 (5): 728–46. doi:10.1002/ccd.22113. PMID 19830793. Retrieved 2011-12-06. Unknown parameter
- ↑ Levine GN, Kern MJ, Berger PB, Brown DL, Klein LW, Kereiakes DJ, Sanborn TA, Jacobs AK (2003). "Management of patients undergoing percutaneous coronary revascularization". Annals of Internal Medicine. 139 (2): 123–36. PMID 12859162. Retrieved 2011-12-06. Unknown parameter
- ↑ Tramèr MR, von Elm E, Loubeyre P, Hauser C (2006). "Pharmacological prevention of serious anaphylactic reactions due to iodinated contrast media: systematic review". BMJ (Clinical Research Ed.). 333 (7570): 675. doi:10.1136/bmj.38905.634132.AE. PMC 1584363. PMID 16880193. Retrieved 2011-12-06. Unknown parameter
- ↑ Greenberger PA, Patterson R, Tapio CM (1985). "Prophylaxis against repeated radiocontrast media reactions in 857 cases. Adverse experience with cimetidine and safety of beta-adrenergic antagonists". Archives of Internal Medicine. 145 (12): 2197–200. PMID 2866755. Retrieved 2011-12-06. Unknown parameter
- ↑ Shehadi WH (1975). "Adverse reactions to intravascularly administered contrast media. A comprehensive study based on a prospective survey". The American Journal of Roentgenology, Radium Therapy, and Nuclear Medicine. 124 (1): 145–52. PMID 1170768. Unknown parameter
- ↑ Gill BV, Rice TR, Cartier A, Gautrin D, Neis B, Horth-Susin L, Jong M, Swanson M, Lehrer SB (2009). "Identification of crab proteins that elicit IgE reactivity in snow crab-processing workers". The Journal of Allergy and Clinical Immunology. 124 (5): 1055–61. doi:10.1016/j.jaci.2009.06.030. PMID 19665776. Retrieved 2011-12-06. Unknown parameter
- ↑ Swoboda I, Bugajska-Schretter A, Verdino P, Keller W, Sperr WR, Valent P, Valenta R, Spitzauer S (2002). "Recombinant carp parvalbumin, the major cross-reactive fish allergen: a tool for diagnosis and therapy of fish allergy". Journal of Immunology (Baltimore, Md. : 1950). 168 (9): 4576–84. PMID 11971005. Retrieved 2011-12-06. Unknown parameter
- ↑ 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.
- Dorland's Illustrated Medical Dictionary (Twenty-sixth Edition) (ISBN 0-7216-1645-3)