MRI contrast agent safety

Though considered safer than the frequently used iodinated contrast agents used in x-ray and CT studies, there are safety issues with MRI contrast agents as well. Paramagnetic metal ions suitable as MR contrast agents are all potentially toxic when injected IV at or near doses needed for clinical imaging. With chelation of these ions, acute toxicity is reduced and elimination rate is increased, thereby reducing the chance of long term toxicity.

Intravenous gadolinium contrast agent safety

See also: nephrogenic systemic fibrosis
Adverse reactions

The most commonly reported reactions associated with the injection of Gd-DTPA are

  • headache (6.5%)
  • injection site coldness (3.6%)
  • injection site pain or burning (2.5%)
  • nausea (1.9%)

Recent adverse rates for Gd-DTPA are lower than this and comparable to those of Gadodiamide and Gadoteridol (1.4%-3% for headache, nausea, and dizziness; <1% for the others). The safety factor or ratio (ratio of the LD50 to the imaging dose) may be used to assess the relative acute toxicity of contrast agents. The elimination half-life for the Gd containing contrast agents range from 1.25-1.6 hours.

Reports of several episodes of severe anaphylactoid reactions after IV injection of Gd- DTPA are published. The frequency of these reactions is about 1 in 100,000 doses. Potential risk factors may include a history of asthma and significant reaction to previously administered iodinated contrast material. It is suggested that the threshold for injecting Gd be raised, in those patients, based on an individual risk/benefit ratio. Prophylactic pharmacotherapy with antihistamines and corticosteriods, such as Greenberger's protocol, is suggested for high risk patients prior to contrast injections 2.

Effect on serum laboratory values

Gadolinium containing contrast agents usually have no effect on blood chemistries and hematologic studies except transient elevation of serum iron and bilirubin levels. These elevations peaked at 4 to 6 hours post injection and returned to baseline values in 24 to 48 hours. The mechanism of these elevations is uncertain but may be related to mild hemolysis. A 10%-11% increase in the activated partial thromboplastin time and thrombin time occurs in vitro with inhibition of platelet aggregation. The platelet aggregation inhibition is less than that seen with iodinated ionic contrast material and no bleeding problems are reported clinically. 

Effect on physiology

Transient and mild drop blood pressure is reported in both animals and humans. A study of 1,068 patients reports hypotension in 0.3% of the subjects and other symptoms such as syncope probably associated with hypotension in 0.8%. Most of these symptoms occur 25-85 minutes after the injection.

Deoxygenated sickle erythrocytes align perpendicular to a magnetic field in in vitro studies raising the possibility of occlusive complications in patients with sickle cell anemia. No clinical reports of this potential problem have been found 1

Retained gadolinium

There are reports that repeated administrations of IV gadolinium contrast leads to T1 shortening in the dentate nuclei, and possibly the globi pallidi 3. This is thought to be related to retained gadolinium contrast at these sites. The effect is thought to be more common with linear gadolinium chelates rather than with cyclic chelates 4,5. Gadolinium is deposited in the brain in patients with normal renal function 3 . Gadolinium retention is not considered to be related to radiation therapy in patients receiving multiple studies for head and neck cancer 6. The clinical effect of this deposition, if any, is currently unknown. However, the phenomenon is currently under investigation by the FDA 7.

 

NOTE: This article was originally transferred from mritutor.org and was last updated in June 23, 2015. Please review and edit if more information becomes available.

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Article Information

rID: 23209
Section: Physics
Tags: refs, mri, safety
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Cases and Figures

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    Case 1: retained gadolinium
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    Case 2: longitudinal series MRI
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    Case 3: longitudinal serial T1 enhancement
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