Radiocontrast agent

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Radiocontrast agents are substances used to enhance the visibility of internal structures in X-ray-based imaging techniques such as computed tomography (contrast CT), projectional radiography, and fluoroscopy. Radiocontrast agents are typically iodine, or more rarely barium sulfate. The contrast agents absorb external X-rays, resulting in decreased exposure on the X-ray detector. This is different from radiopharmaceuticals used in nuclear medicine which emit radiation.

Contents

Magnetic resonance imaging (MRI) functions through different principles and thus MRI contrast agents have a different mode of action. These compounds work by altering the magnetic properties of nearby hydrogen nuclei.

Types and uses

Radiocontrast agents used in X-ray examinations can be grouped in positive (iodinated agents, barium sulfate), and negative agents (air, carbon dioxide, methylcellulose). [1]

Iodine (circulatory system)

Example of iodine based contrast in cerebral angiography Cerebral Angiogram Lateral.jpg
Example of iodine based contrast in cerebral angiography

Iodinated contrast contains iodine. It is the main type of radiocontrast used for intravenous administration. Iodine has a particular advantage as a contrast agent for radiography because its innermost electron ("k-shell") binding energy is 33.2 keV, similar to the average energy of x-rays used in diagnostic radiography. When the incident x-ray energy is closer to the k-edge of the atom it encounters, photoelectric absorption is more likely to occur. Its uses include:

Organic iodine molecules used for contrast include iohexol, iodixanol and ioversol.

Barium sulfate (digestive system)

Example of a DCBE Human intestinal tract, as imaged via double-contrast barium enema.jpg
Example of a DCBE

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.[ citation needed ]

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 as a barium sulfate suspension or administered as an enema. After the examination, it leaves the body with the feces.

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 visualized.

Before the advent of modern neuroimaging techniques, air or other gases were used as contrast agents employed to displace the cerebrospinal fluid in the brain while performing a pneumoencephalography. Sometimes called an "air study", this once common yet highly-unpleasant procedure was used to enhance the outline of structures in the brain, looking for shape distortions caused by the presence of lesions.

Carbon dioxide

Carbon dioxide also has a role in angioplasty. It is low-risk as it is a natural product with no risk of allergic potential. However, it can be used only below the diaphragm as there is a risk of embolism in neurovascular procedures. It must be used carefully to avoid contamination with room air when injected. It is a negative contrast agent in that it displaces blood when injected intravascularly.

Discontinued agents

Thorotrast

Thorotrast was a contrast agent based on thorium dioxide, which is radioactive. It was first introduced in 1929. While it provided good image enhancement, its use was abandoned in the late 1950s since it turned out to be carcinogenic. Given that the substance remained in the bodies of those to whom it was administered, it gave a continuous radiation exposure and was associated with a risk of cancers of the liver, bile ducts and bones, as well as higher rates of hematological malignancy (leukemia and lymphoma). [2] Thorotrast may have been administered to millions of patients prior to being disused.[ citation needed ]

Nonsoluble substances

In the past, some non water-soluble contrast agents were used. One such substance was iofendylate (trade names: Pantopaque, Myodil) which was an iodinated oil-based substance that was commonly used in myelography. Due to it being oil-based, it was recommended that the physician remove it from the patient at the end of the procedure. This was a painful and difficult step and because complete removal could not always be achieved, iofendylate's persistence in the body might sometimes lead to arachnoiditis, a potentially painful and debilitating lifelong disorder of the spine. [3] [4] Iofendylate's use ceased when water-soluble agents (such as metrizamide) became available in the late 1970s. Also, with the advent of MRI, myelography became much less-commonly performed.

Adverse effects

Modern iodinated contrast agents – especially non-ionic compounds – are generally well tolerated. [5] The adverse effects of radiocontrast can be subdivided into type A reactions (e.g. thyrotoxicosis), and type B reactions (hypersensitivity reactions: allergy and non-allergy reactions [formerly called 'anaphylactoid reactions']). [6]

Patients receiving contrast via IV typically experience a hot feeling around the throat, and this hot sensation gradually moves down to the pelvic area.

The documentation of adverse drug reactions to contrast media should be documented precisely so that the patient receives adequate prophylaxis if contrast medium is administered again. [7]

Contrast induced nephropathy

Iodinated contrast may be toxic to the kidneys, especially when given via the arteries prior to studies such as catheter coronary angiography. Non-ionic contrast agents, which are almost exclusively used in computed tomography studies, have not been shown to cause CIN when given intravenously at doses needed for CT studies. [8]

Thyroid dysfunction

Iodinated radiocontrast can induce overactivity (hyperthyroidism) and underactivity (hypothyroidism) of the thyroid gland. The risk of either condition developing after a single examination is 2–3 times that of those who have not undergone a scan with iodinated contrast. Thyroid underactivity is mediated by two phenomena called the Plummer and Wolff–Chaikoff effect, where iodine suppresses the production of thyroid hormones; this is usually temporary but there is an association with longer-term thyroid underactivity. Some other people show the opposite effect, called Jod-Basedow phenomenon, where the iodine induces overproduction of thyroid hormone; this may be the result of underlying thyroid disease (such as nodules or Graves' disease) or previous iodine deficiency. Children exposed to iodinated contrast during pregnancy may develop hypothyroidism after birth and monitoring of the thyroid function is recommended. [9]

See also

Related Research Articles

<span class="mw-page-title-main">Radiology</span> Branch of Medicine

Radiology is the medical discipline that uses medical imaging to diagnose diseases and guide their treatment, within the bodies of humans and other animals. It began with radiography, but today it includes all imaging modalities, including those that use no electromagnetic radiation, as well as others that do, such as computed tomography (CT), fluoroscopy, and nuclear medicine including positron emission tomography (PET). Interventional radiology is the performance of usually minimally invasive medical procedures with the guidance of imaging technologies such as those mentioned above.

<span class="mw-page-title-main">Lower gastrointestinal series</span> Radiographs used to examine abnormalities of the colon

A lower gastrointestinal series is a medical procedure used to examine and diagnose problems with the human colon of the large intestine. Radiographs are taken while barium sulfate, a radiocontrast agent, fills the colon via an enema through the rectum.

<span class="mw-page-title-main">Fluoroscopy</span> Production of an image when X-rays strike a fluorescent screen

Fluoroscopy is an imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope allows a surgeon to see the internal structure and function of a patient, so that the pumping action of the heart or the motion of swallowing, for example, can be watched. This is useful for both diagnosis and therapy and occurs in general radiology, interventional radiology, and image-guided surgery.

<span class="mw-page-title-main">Upper gastrointestinal series</span> Radiographs used to examine abnormalities of the digestive system excluding the colon

An upper gastrointestinal series, also called a barium swallow, barium study, or barium meal, is a series of radiographs used to examine the gastrointestinal tract for abnormalities. A contrast medium, usually a radiocontrast agent such as barium sulfate mixed with water, is ingested or instilled into the gastrointestinal tract, and X-rays are used to create radiographs of the regions of interest. The barium enhances the visibility of the relevant parts of the gastrointestinal tract by coating the inside wall of the tract and appearing white on the film. This in combination with other plain radiographs allows for the imaging of parts of the upper gastrointestinal tract such as the pharynx, larynx, esophagus, stomach, and small intestine such that the inside wall lining, size, shape, contour, and patency are visible to the examiner. With fluoroscopy, it is also possible to visualize the functional movement of examined organs such as swallowing, peristalsis, or sphincter closure. Depending on the organs to be examined, barium radiographs can be classified into "barium swallow", "barium meal", "barium follow-through", and "enteroclysis". To further enhance the quality of images, air or gas is sometimes introduced into the gastrointestinal tract in addition to barium, and this procedure is called double-contrast imaging. In this case the gas is referred to as the negative contrast medium. Traditionally the images produced with barium contrast are made with plain-film radiography, but computed tomography is also used in combination with barium contrast, in which case the procedure is called "CT enterography".

<span class="mw-page-title-main">Thorotrast</span> Contrast agent for imaging, no longer used clinically

Thorotrast is a suspension containing particles of the radioactive compound thorium dioxide, ThO2; it was used as a radiocontrast agent in clinical radiography in the 1930s to 1950s. It is no longer used clinically.

Radiodensity is opacity to the radio wave and X-ray portion of the electromagnetic spectrum: that is, the relative inability of those kinds of electromagnetic radiation to pass through a particular material. Radiolucency or hypodensity indicates greater passage to X-ray photons and is the analogue of transparency and translucency with visible light. Materials that inhibit the passage of electromagnetic radiation are called radiodense or radiopaque, while those that allow radiation to pass more freely are referred to as radiolucent. Radiopaque volumes of material have white appearance on radiographs, compared with the relatively darker appearance of radiolucent volumes. For example, on typical radiographs, bones look white or light gray (radiopaque), whereas muscle and skin look black or dark gray, being mostly invisible (radiolucent).

<span class="mw-page-title-main">Iodinated contrast</span> Substance to enhance X-ray imaging

Iodinated contrast is a form of water-soluble, intravenous radiocontrast agent containing iodine, which enhances the visibility of vascular structures and organs during radiographic procedures. Some pathologies, such as cancer, have particularly improved visibility with iodinated contrast.

<span class="mw-page-title-main">Iotrolan</span> Chemical compound

Iotrolan is an iodine-containing radiocontrast agent, a substance used to improve the visibility of body structures on images obtained by X-ray techniques.

<span class="mw-page-title-main">Diatrizoate</span> Chemical compound

Diatrizoate, also known as amidotrizoate, Gastrografin, is a contrast agent used during X-ray imaging. This includes visualizing veins, the urinary system, spleen, and joints, as well as computer tomography. It is given by mouth, injection into a vein, injection into the bladder, through a nasogastric tube, or rectally.

A contrast agent is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiopharmaceuticals, which emit radiation themselves. In x-ray imaging, contrast agents enhance the radiodensity in a target tissue or structure. In magnetic resonance imaging, contrast agents shorten the relaxation times of nuclei within body tissues in order to alter the contrast in the image.

<span class="mw-page-title-main">Myelography</span> Medical Imaging Technique

Myelography is a type of radiographic examination that uses a contrast medium to detect pathology of the spinal cord, including the location of a spinal cord injury, cysts, and tumors. Historically the procedure involved the injection of a radiocontrast agent into the cervical or lumbar spine, followed by several X-ray projections. Today, myelography has largely been replaced by the use of MRI scans, although the technique is still sometimes used under certain circumstances – though now usually in conjunction with CT rather than X-ray projections.

Pyelogram is a form of imaging of the renal pelvis and ureter.

<span class="mw-page-title-main">Abdominal x-ray</span>

An abdominal x-ray is an x-ray of the abdomen. It is sometimes abbreviated to AXR, or KUB.

<span class="mw-page-title-main">Double-contrast barium enema</span>

A double-contrast barium enema is a form of contrast radiography in which x-rays of the colon and rectum are taken using two forms of contrast to make the structures easier to see. A liquid containing barium is put into the rectum. Barium outlines the colon and rectum on an x-ray and helps show abnormalities. Air is also put into the rectum and colon to further enhance the x-ray.

<span class="mw-page-title-main">Iopromide</span> Chemical compound

Iopromide is an iodinated contrast medium for X-ray imaging. 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; i.e., it is injected into blood vessels.

<span class="mw-page-title-main">Iopentol</span> Chemical compound

Iopentol is a pharmaceutical drug that was used as a radiocontrast agent for X-ray imaging in Europe.

<span class="mw-page-title-main">Iobitridol</span> Pharmaceutical drug

Iobitridol is a pharmaceutical drug used as a radiocontrast agent in X-ray imaging. It is injected into blood vessels, joints, or body cavities such as the uterus, and filtered out by the kidneys. Its most common adverse effect is nausea. Severe allergic reactions are rare.

<span class="mw-page-title-main">Ioxaglic acid</span> Chemical compound

Ioxaglic acid is pharmaceutical drug used as an iodinated contrast medium for X-ray imaging. It has low osmolality, typically resulting in fewer side effects than high-osmolality media. It is manufactured by Guerbet, but marketing in the US has been discontinued. As of 2021, it may still be available in some European countries.

<span class="mw-page-title-main">Contrast CT</span>

Contrast CT, or contrast enhanced computed tomography (CECT), is X-ray computed tomography (CT) using radiocontrast. Radiocontrasts for X-ray CT are generally iodine-based types. This is useful to highlight structures such as blood vessels that otherwise would be difficult to delineate from their surroundings. Using contrast material can also help to obtain functional information about tissues. Often, images are taken both with and without radiocontrast. CT images are called precontrast or native-phase images before any radiocontrast has been administered, and postcontrast after radiocontrast administration.

<span class="mw-page-title-main">Medical imaging in pregnancy</span> Types of pregnancy imaging techniques

Medical imaging in pregnancy may be indicated because of pregnancy complications, intercurrent diseases or routine prenatal care.

References

  1. ↑ Dong, Yuxy C; Cormode, David P. (2021). "Chapter 17. Heavy Elements for X-Ray Contrast". Metal Ions in Bio-Imaging Techniques. Springer. pp. 457–484. doi:10.1515/9783110685701-023. S2CID   233676619.
  2. ↑ Grosche, B.; Birschwilks, M.; Wesch, H.; Kaul, A.; van Kaick, G. (6 May 2016). "The German Thorotrast Cohort Study: a review and how to get access to the data". Radiation and Environmental Biophysics. 55 (3): 281–289. doi:10.1007/s00411-016-0651-8. PMID   27154786. S2CID   45053720.
  3. ↑ Dunlevy, Sue (10 December 2016). "Australians crippled and in chronic pain from dye used in toxic X-rays". The Daily Telegraph (Sydney) . Retrieved 27 October 2017.
  4. ↑ William P. Dillon; Christopher F. Dowd (2014). "Chapter 53 – Neurologic Complications of Imaging Procedures". Aminoff's Neurology and General Medicine (5th ed.). pp. 1089–1105.
  5. ↑ Haberfeld, H, ed. (2009). Austria-Codex (in German) (2009/2010 ed.). Vienna: Österreichischer Apothekerverlag. ISBN   978-3-85200-196-8.
  6. ↑ Boehm I, Morelli J, Nairz K, Silva Hasembank Keller P, Heverhagen JT (2017). "Myths and misconceptions concerning contrast media induced anaphylaxis: a narrative review". Postgrad Med. 129 (2): 259–266. doi:10.1080/00325481.2017.1282296. PMID   28085538. S2CID   205452727.
  7. ↑ Böhm IB, van der Molen AJ (2020). "Recommendations for Standardized Documentation of Contrast Medium-Induced Hypersensitivity". J Am Coll Radiol. 17 (8): 1027–1028. doi:10.1016/j.jacr.2020.02.007. hdl: 1887/3184447 . PMID   32142634.
  8. ↑ McDonald, Robert; McDonald, Jennifer S.; Carter, Rickey E.; Hartman, Robert P.; Katzberg, Richard W.; Kallmes, David F.; Williamson, Eric E. (December 2014). "Intravenous Contrast Material Exposure Is Not an Independent Risk Factor for Dialysis or Mortality". Radiology. 273 (3): 714–725. doi:10.1148/radiol.14132418. PMID   25203000.
  9. ↑ Lee SY, Rhee CM, Leung AM, Braverman LE, Brent GA, Pearce EN (6 November 2014). "A Review: Radiographic Iodinated Contrast Media-Induced Thyroid Dysfunction". J Clin Endocrinol Metab. 100 (2): 376–83. doi:10.1210/jc.2014-3292. PMC   4318903 . PMID   25375985.

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