Radiocontrast
Encyclopedia
Radiocontrast agents are a type of medical contrast medium
used to improve the visibility of internal bodily structures in an X-ray
based imaging techniques such as computed tomography
(CT) or radiography
(commonly known as X-ray imaging). Radiocontrast agents are typically iodine
or barium
compounds.
Despite being part of radiology, magnetic resonance imaging
(MRI) functions through different principles and thus utilizes different contrast agents
. These compounds work by altering the magnetic properties of nearby hydrogen nuclei.
examinations can be grouped based on its use.
Iodine based contrast media are usually classified as ionic or non-ionic. Both types are used most commonly in radiology, due to its relatively harmless interaction with the body and its solubility. It is primarily used to visualize vessels, and changes in tissues on radiography and CT, but can also be used for tests of the urinary tract, uterus and fallopian tubes. It may cause the patient to feel as if he or she has urinated on himself. It also puts a metallic taste in the mouth of the patient.
Modern intravenous contrast agents are typically based on iodine. This may be bound either in an organic (non-ionic) compound or an ionic compound. Ionic agents were developed first and are still in widespread use depending on the requirements but may result in additional complications. Organic agents which covalently bind the iodine have fewer side effects as they do not dissociate into component molecules. Many of the side effects are due to the hyperosmolar solution being injected. i.e. they deliver more iodine atoms per molecule. The more iodine, the more "dense" the X-ray effect.
There are many different molecules. Some examples of organic iodine molecules are iohexol
, iodixanol
and ioversol
.
Iodine based contrast media are water soluble and harmless to the body. These contrast agents are sold as clear colorless water solutions, the concentration is usually expressed as mg I/ml. Modern iodinated contrast agents can be used almost anywhere in the body. Most often they are used intravenously, but for various purposes they can also be used intraarterially, intrathecally (as in diskography of the spine) and intraabdominally – just about any body cavity or potential space.
Iodine contrast agents are used for the following:
, Telebrix, etc.
, iopromide
, iodixanol
, etc.
Barium sulfate
is mainly used in the imaging of the digestive system. The substance exists as a water insoluble white powder that is made into a slurry with water and administered directly into the gastrointestinal tract
.
Barium sulfate, an insoluble white powder is typically used for enhancing contrast in the GI tract. Depending on how it is to be administered the compound is mixed with water, thickeners, de-clumping agents, and flavourings to make the contrast agent. As the barium sulfate doesn't dissolve, this type of contrast agent is an opaque white mixture. It is only used in the digestive tract; it is usually swallowed or administered as an enema. After the examination, it leaves the body with the feces
.
was based on thorium dioxide
, but this was abandoned since it turned out to be carcinogenic.
They are similar in presentation to anaphylactic reactions
, but are not caused by an IgE-mediated immune response. Patients with a history of contrast reactions, however, are at increased risk of anaphylactoid reactions.
Pretreatment with corticosteroids has been shown to decrease the incidence of adverse reactions.
Anaphylactoid reactions range from urticaria
and itching, to bronchospasm
and facial and laryngeal edema
. For simple cases of urticaria and itching, Benadryl (diphenhydramine
) oral or IV is appropriate. For more severe reactions, including bronchospasm and facial or neck edema, albuterol inhaler, or subcutaneous or IV epinephrine, plus diphenhydramine may be needed. If respiration is compromised, an airway must be established prior to medical management.
is defined as either a greater than 25% increase of serum creatinine or an absolute increase in serum creatinine of 0.5 mg/dL.
, 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 less than 100 ml 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.
Contrast medium
A medical contrast medium is a substance used to enhance the contrast of structures or fluids within the body in medical imaging...
used to improve the visibility of internal bodily structures in an X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
based imaging techniques such as computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
(CT) or radiography
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....
(commonly known as X-ray imaging). Radiocontrast agents are typically iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
or barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
compounds.
Despite being part of radiology, magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI) functions through different principles and thus utilizes different contrast agents
MRI contrast agent
MRI contrast agents are a group of contrast media used to improve the visibility of internal body structures in magnetic resonance imaging . The most commonly used compounds for contrast enhancement are gadolinium-based. MRI contrast agents alter the relaxation times of tissues and body cavities...
. These compounds work by altering the magnetic properties of nearby hydrogen nuclei.
Types and uses
Radiocontrast agents used in X-rayX-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
examinations can be grouped based on its use.
Iodinated (intravascular)
Modern intravenous contrast agents are typically based on iodine. This may be bound either in an organic (non-ionic) compound or an ionic compound. Ionic agents were developed first and are still in widespread use depending on the requirements but may result in additional complications. Organic agents which covalently bind the iodine have fewer side effects as they do not dissociate into component molecules. Many of the side effects are due to the hyperosmolar solution being injected. i.e. they deliver more iodine atoms per molecule. The more iodine, the more "dense" the X-ray effect.
There are many different molecules. Some examples of organic iodine molecules are iohexol
Iohexol
Iohexol is a contrast agent, sold under the trade name Omnipaque. It is available in various concentrations, from 140 to 350 milligrams of iodine per milliliter...
, iodixanol
Iodixanol
Iodixanol is a contrast agent, sold under the trade name Visipaque. Visipaque is commonly used as a contrast agent during coronary angiography. It is the only iso-osmolar contrast agent, with an osmolality of 290 mOsm/kg H2O, the same as blood. It is sold in 2 main concentrations 270 mgI/ml and...
and ioversol
Ioversol
Ioversol is an organoiodine compound that used as a contrast medium. It features both a high iodine content, as well as several hydrophilic groups....
.
Iodine based contrast media are water soluble and harmless to the body. These contrast agents are sold as clear colorless water solutions, the concentration is usually expressed as mg I/ml. Modern iodinated contrast agents can be used almost anywhere in the body. Most often they are used intravenously, but for various purposes they can also be used intraarterially, intrathecally (as in diskography of the spine) and intraabdominally – just about any body cavity or potential space.
Iodine contrast agents are used for the following:
- Angiography (arterial investigations)
- VenographyVenographyVenography is a procedure in which an x-ray of the veins, a venogram, is taken after a special dye is injected into the bone marrow or veins. The dye has to be injected constantly via a catheter, making it an invasive procedure...
(venous investigations) - VCUG (voiding cystourethrography)
- HSG (hysterosalpinogram)
- IVU (intravenous urography)
High osmolar (ionic)
Ionic contrast media have higher osmolarity and more side-effects, such as diatrizoic acidDiatrizoic acid
Diatrizoic acid , also known as amidotrizoic acid, or 3,5-diacetamido-2,4,6-triiodobenzoic acid, is a radiocontrast agent containing iodine. Trade names include Hypaque, Gastrografin and Urografin, the latter being a combination of the sodium and meglumine salts.Diatrizoate is considered a...
, Telebrix, etc.
| Compound | Name | Type | Iodine content | Osmolality | Level |
|---|---|---|---|---|---|
| Ionic | Diatrizoate (Hypaque 50) | Monomer | 300 mgI/ml | 1550 | High osmolar |
| Ionic | Metrizoate (Isopaque 370) | Monomer | 370 mgI/ml | 2100 | High osmolar |
| Ionic | Ioxaglate (Hexabrix) | Dimer | 320 mgI/ml | 580 | High osmolar |
Low osmolar (non-ionic)
Non-ionic contrast media, have lower osmolarity and tend to have fewer side-effects, such as iohexolIohexol
Iohexol is a contrast agent, sold under the trade name Omnipaque. It is available in various concentrations, from 140 to 350 milligrams of iodine per milliliter...
, iopromide
Iopromide
Iopromide is a molecule used as a contrast medium. It is marketed under the name Ultravist which is produced by Bayer Healthcare. It is a low osmolar, non-ionic contrast agent for intravascular use....
, iodixanol
Iodixanol
Iodixanol is a contrast agent, sold under the trade name Visipaque. Visipaque is commonly used as a contrast agent during coronary angiography. It is the only iso-osmolar contrast agent, with an osmolality of 290 mOsm/kg H2O, the same as blood. It is sold in 2 main concentrations 270 mgI/ml and...
, etc.
| Compound | Name | Type | Iodine content | Osmolality | Level |
|---|---|---|---|---|---|
| Non-ionic | Iopamidol Iopamidol Iopamidol is a nonionic, low-osmolar iodinated contrast agent, developed by Bracco.It is available in various concentrations, from 200 to 370 mgI/mL.-Clinical uses:... (Isovue 370) |
Monomer | 370 mgI/ml | 796 | Low osmolar |
| Non-ionic | Iohexol Iohexol Iohexol is a contrast agent, sold under the trade name Omnipaque. It is available in various concentrations, from 140 to 350 milligrams of iodine per milliliter... (Omnipaque 350) |
Monomer | 350 mgI/ml | 884 | Low osmolar |
| Non-ionic | Ioxilan Ioxilan Ioxilan is a diagnostic contrast agent. It is injected intravenously before taking X-ray images to increase arterial contrast in the final image. It is marketed under the trade name Oxilan by Guerbet, L.L.C.... (Oxilan 350) |
Monomer | 350 mgI/ml | 695 | Low osmolar |
| Non-ionic | Iopromide Iopromide Iopromide is a molecule used as a contrast medium. It is marketed under the name Ultravist which is produced by Bayer Healthcare. It is a low osmolar, non-ionic contrast agent for intravascular use.... (Ultravist 370) |
Monomer | 370 mgI/ml | 774 | Low osmolar |
| Non-ionic | Iodixanol Iodixanol Iodixanol is a contrast agent, sold under the trade name Visipaque. Visipaque is commonly used as a contrast agent during coronary angiography. It is the only iso-osmolar contrast agent, with an osmolality of 290 mOsm/kg H2O, the same as blood. It is sold in 2 main concentrations 270 mgI/ml and... (Visipaque 320) |
Dimer | 320 mgI/ml | 290 | Low osmolar |
Barium (gastro-intestinal)
Barium sulfate
Barium sulfate is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it...
is mainly used in the imaging of the digestive system. The substance exists as a water insoluble white powder that is made into a slurry with water and administered directly into the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
.
- Barium enema (large bowel investigation) and DCBE (double contrast barium enema)
- Barium swallow (oesophagael investigation)
- Barium meal (stomach investigation) and double contrast barium meal
- Barium follow through (stomach and small bowel investigation)
- CT pneumocolon / virtual colonoscopy
Barium sulfate, an insoluble white powder is typically used for enhancing contrast in the GI tract. Depending on how it is to be administered the compound is mixed with water, thickeners, de-clumping agents, and flavourings to make the contrast agent. As the barium sulfate doesn't dissolve, this type of contrast agent is an opaque white mixture. It is only used in the digestive tract; it is usually swallowed or administered as an enema. After the examination, it leaves the body with the feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
.
Air
As in the picture on the right where both air and barium are used together (hence the term "double-contrast" barium enema) air can be used as a contrast material because it is less radio-opaque than the tissues it is defining. In the picture it highlights the interior of the colon. An example of a technique using purely air for the contrast medium is an air arthrogram where the injection of air into a joint cavity allows the cartilage covering the ends of the bones to be visualised.Other
An older type of contrast agent, ThorotrastThorotrast
Thorotrast is a suspension containing particles of the radioactive compound thorium dioxide, ThO2, used as a contrast medium in X-ray diagnostics in the 1930s and 40s ....
was based on thorium dioxide
Thorium dioxide
Thorium dioxide , also called thorium oxide is a white, crystalline powder. It was formerly known as thoria or thorina. It is produced mainly as a by-product of lanthanide and uranium production.[1]...
, but this was abandoned since it turned out to be carcinogenic.
Adverse effects
Modern iodinated contrast agents are safe drugs; adverse reactions exist but they are uncommon. The major side effects of radiocontrast are anaphylactoid reactions and contrast-induced nephropathy.Anaphylactoid reactions
Anaphylactoid reactions occur rarely, but can occur in response to injected as well as oral and rectal contrast and even retrograde pyelography.They are similar in presentation to anaphylactic reactions
Anaphylaxis
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...
, but are not caused by an IgE-mediated immune response. Patients with a history of contrast reactions, however, are at increased risk of anaphylactoid reactions.
Pretreatment with corticosteroids has been shown to decrease the incidence of adverse reactions.
Anaphylactoid reactions range from urticaria
Urticaria
Urticaria is a kind of skin rash notable for pale red, raised, itchy bumps. Hives is frequently caused by allergic reactions; however, there are many non-allergic causes...
and itching, to bronchospasm
Bronchospasm
Bronchospasm or a bronchial spasm is a sudden constriction of the muscles in the walls of the bronchioles. It is caused by the release of substances from mast cells or basophils under the influence of anaphylatoxins...
and facial and laryngeal edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
. For simple cases of urticaria and itching, Benadryl (diphenhydramine
Diphenhydramine
Diphenhydramine hydrochloride is a first-generation antihistamine possessing anticholinergic, antitussive, antiemetic, and sedative properties which is mainly used to treat allergies. Like most other first-generation antihistamines, the drug also has a powerful hypnotic effect, and for this reason...
) oral or IV is appropriate. For more severe reactions, including bronchospasm and facial or neck edema, albuterol inhaler, or subcutaneous or IV epinephrine, plus diphenhydramine may be needed. If respiration is compromised, an airway must be established prior to medical management.
Contribution of seafood and other allergies
There are no true allergies against iodine. Suspicion of seafood "allergy" is not a sufficient contraindication to the use of iodinated contrast material. While iodine levels in seafood are higher than in non-seafood items, the consumption of the latter exceeds that of the former by far and there is no evidence that the iodine content of seafood is related to reactions to seafood. Available data suggest that seafood allergy increases the risk of a contrast-mediated reaction by approximately the same amount as allergies to fruits or those with asthma. In other words, over 85% of patients with seafood allergies will not have an adverse reaction to iodinated contrast. Finally, there is no evidence that adverse skin reactions to iodine-containing topical antiseptics (e.g., povidone-iodine) are of any specific relevance to administration of I.V. contrast material.Contrast-induced nephropathy
Contrast-induced nephropathyNephropathy
Nephropathy refers to damage to or disease of the kidney. An older term for this is nephrosis.-Causes:Causes of nephropathy include administration of analgesics, xanthine oxidase deficiency, and long-term exposure to lead or its salts...
is defined as either a greater than 25% increase of serum creatinine or an absolute increase in serum creatinine of 0.5 mg/dL.
Drug interactions
It has been recommended that metforminMetformin
Metformin is an oral antidiabetic drug in the biguanide class. It is the first-line drug of choice for the treatment of type 2 diabetes, in particular, in overweight and obese people and those with normal kidney function. Its use in gestational diabetes has been limited by safety concerns...
, 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
Lactic acidosis
Lactic acidosis is a physiological condition characterized by low pH in body tissues and blood accompanied by the buildup of lactate especially D-lactate, and is considered a distinct form of metabolic acidosis. The condition typically occurs when cells receive too little oxygen , for example...
, a dangerous complication.
However, guidelines published by the Royal College of Radiologists suggest this is not as important for patients who receive less than 100 ml of contrast media and have normal renal function
Creatinine
Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body...
. If renal impairment is found before administration of the contrast, metformin should be stopped 48 hours before and after the procedure.