MadSci Network: Medicine

Re: Why is gadolinium used in MRI and how long does it stay in the body?

Date: Mon Feb 2 23:05:21 1998
Posted By: Ray Hsu, Medical Student, School of Medicine, Washington University
Area of science: Medicine
ID: 884803971.Me

Dear Margaret:

Thanks for your question.

Magnetic resonance (MR) contrast agents are unique in radiology because it
is not the chemical that is detected, but rather the effect that the
chemical has on surrounding molecules that is detected.

MR imaging relies on signal originating from hydrogen nuclei in water and
fat.  These protons have properties known as T1 and T2 relaxation, which
vary depend on the immediate surroundings, and affect signal magnitude from
the given region.  MR imaging uses various magnetic field changes to
accentuate the difference in signal magnitudes from different regions.  The
reason that different anatomic structures can be seen on an MRI is largely
due to differences in T1 and T2 between different tissues.

Gadolinium (chelated to a carrier molecule) is an intravenously-injected MR
contrast agent which shortens the T1 of surrounding protons, making them
appear brighter.  Because gadolinium normally stays in blood vessels, it
has the effect of making vessels, highly vascular tissues, and areas of
blood leakage appear brighter.

Gadolinium is excreted through the kidneys, with a half-life of 1.25-1.6

				Ray Hsu

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