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MRI Contrast
MRI Contrast
MRI is based on magnetization, not
ionizing radiation. Therefore, the intravenous contrast
material must have magnetic properties different from that of the
surrounding tissue. The most common agent used is gadolinium
diethylenetriamine pentaacetic acid (Gd-DTPA) — a paramagnetic agent
that allows positive contrast enhancement, i.e. it shows up as
bright on T1-weighted sequences. This provides a new array of
diagnostic information, including differentiation of tumor from
edema and inflammation and soft tissue from scar tissue (as in
recurrent lumbar disc herniation). It also facilitates the dynamic assessment
of lesion types such as hepatic hemangiomas vs hepatocellular
carcinoma). In the brain, Gd-enhancement reveals areas where the
blood-brain barrier has been breached, providing vital information
on patients with tumors and other pathologic processes. For multiple
sclerosis, Gd-enhancement helps distinguish active demyelination
plaques from chronic quiescent ones. Other valuable uses for Gd in
brain MRIs include the assessment of early ischemia, parenchymal
brain infections and meningeal lesions. MRI contrast is felt to be a safe contrast agent that rarely
causes allergic reactions. It is important, however, that the
patient with impaired kidney function not receive MRI contrast.
Patients with the following history are required to have a recent
BUN and creatinine/glomeular filtration rate (GFR) assessment prior
to receiving intravenous MRI contrast.
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