Iodinated contrast media

Dr Craig Hacking and Mr Andrew Murphy et al.

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 etc.

Basic overview

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, nonionic 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

Intravenous

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.

Intraosseous

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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Article information

rID: 48582
Sections: Radiography, Physics
Synonyms or Alternate Spellings:
  • Iodinated contrast media
  • Iodinated contrast medium
  • Iodine-containing contrast media
  • Iodine-containing contrast medium
  • Contrast

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