Iodinated contrast media are contrast agents frequently used via intravenous administration in computed tomography, although they are also used in fluoroscopy, angiography and venography, and even occasionally, plain radiography. Although the intravenous route is common, they are also administered by many other routes including orally, per rectally, per vaginally, per urethral, intraosseous etc.
Iodine has a particular advantage as a contrast agent because the k-shell binding energy of 33.2 KeV is similar to that of the average energy of diagnostic radiography 1. Consequently, it will have an increased attenuation compared to the anatomical structures that surround it.
There are two main types of iodinated contrast media, the first, is comprised of a single benzene ring where three iodine atoms are attached and are known as monomeric agents, the second possesses two tri-iodinated benzene rings and are known as dimeric agents 2.
The contrast agents are then classified, via their water solubility as ionic or non-ionic.
Ionic agents, disperse into negative and positive ions, and hence have a higher toxicity; while the non-ionic agents do not. Therefore, non-ionic agents, are used conventionally now, often containing additional polar -OH groups that make them water-soluble 3.
Non-ionic contrast agents are available in varying concentrations ranging from 240 to 400 mg iodine/mL, the higher the concentration, the greater the peak of enhancement (measured in Hounsfield units), however, it will become more viscous.
Anaphylactic-type reactions to iodinated contrast agents are rare, accounting for 0.6% of cases with only 0.04% considered aggressive 9. It is now known that patients who suffer from allergic reactions to shellfish or topical iodine are not at any higher risk of contrast allergy than the general population 10,11.
However, patients that have a known history of asthma have slightly elevated chances of an allergic-type reaction to the injection 12.
The pre-warming of contrast agents, particular ones of higher concentration (370 mg/mL) will lower the chances of contrast extravasation 5.
Injection of contrast
Contrast injected intravenously is often mechanical via a computerised pressure injector. The American College of Radiology recommends a cannula of 20-gauge or larger for the mechanical injection of intravenous contrast for any injections that require a flow rate higher than 3 mL/s 6.
In the context of the critically ill patient where intravenous access is not possible, iodinated contrast can be administered via an intraosseous injection. Pressure rates must be high due to the intramedullary pressure within the bone. According to the ACR Committee on Drugs and Contrast Media, there are no reported complications of intraosseous injections at 5 mL/s 6. The humerus is the most commonly accepted site of injection 7,8.
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- 2. Jonathan Clayden, Nick Greeves, Stuart Warren. Organic Chemistry. ISBN: 9780199270293
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- 6. ACR Manual on Contrast Media. ACR Manual on Contrast Media. ACR Committee on Drugs and Contrast Media, 2017. [Link].
- 7. Knuth TE, Paxton JH, Myers D. Intraosseous injection of iodinated computed tomography contrast agent in an adult blunt trauma patient. Annals of emergency medicine. 57 (4): 382-6. doi:10.1016/j.annemergmed.2010.09.025 - Pubmed
- 8. Philbeck TE, Miller LJ, Montez D, Puga T. Hurts so good. Easing IO pain and pressure. JEMS : a journal of emergency medical services. 35 (9): 58-62, 65-6, 68; quiz 69. doi:10.1016/S0197-2510(10)70232-1 - Pubmed
- 9. Wang CL, Cohan RH, Ellis JH, Caoili EM, Wang G, Francis IR. Frequency, outcome, and appropriateness of treatment of nonionic iodinated contrast media reactions. AJR. American journal of roentgenology. 191 (2): 409-15. doi:10.2214/AJR.07.3421 - Pubmed
- 10. Beaty AD, Lieberman PL, Slavin RG. Seafood allergy and radiocontrast media: are physicians propagating a myth?. The American journal of medicine. 121 (2): 158.e1-4. doi:10.1016/j.amjmed.2007.08.025 - Pubmed
- 11.Boehm I. Seafood allergy and radiocontrast media: are physicians propagating a myth?. The American journal of medicine. 121 (8): e19. doi:10.1016/j.amjmed.2008.03.035 - Pubmed
- 12. Shehadi WH. 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. Pubmed
computed tomography (CT)
- CT technology
- CT image reconstruction
- CT image quality
- CT dose
- CT contrast
- patient-based artifacts
- physics-based artifacts
- hardware-based artifacts
- helical and multichannel artifacts
- CT safety
- history of CT