Wednesday, October 29, 2008

Gadolinium and MR Arthrography

We do a great deal of MR arthrography in our practice. In this test the radiologist first instills contrast into the joint, typically under imaging guidance. Immediately thereafter, the patient has an MR examination. The contrast that is typically used for this examination is dilute gadolinium, mixed in iodinated contrast, saline, or a mixture of the two. There have been excellent articles published about what concentration of gadolinium to use; for example, see this article by Montgomery et al.

I have seen some unusual contrast properties on various MRI pulse sequences, sometimes varying with the brand of iodinated contrast that is used in the cocktail. I finally decided to try to gather some additional data, to see how various mixtures performed under the pulse sequence parameters that we use.

The following graph summarizes the results:

Saline = normal saline
Iodine = iodinated contrast (240mg iodine/ml)
Gad = Magnevist
The graph plots the signal intensity for several different mixtures, using sequences routinely used for MRI arthrography at 1.5 Tesla.

There are a number of interesting conclusions that can be drawn from this data. Most importantly, the highest signal intensity for all pulse sequences is obtained by using a 1:1 mixture of iodinated contrast and normal saline, with a gadolinium concentration of 1.25 mmol/L. This is the mixture we currently use for MR arthrography. Next, signal intensity for T2 weighted sequences is lower for all mixtures when one goes from TE=36 ms to a TE=70 ms. This is not surprising, but emphasizes that one should use TE values that are at the lower end of T2 values that give T2 weighting.

MR arthrography, properly done, is an excellent test that can give a great deal of valuable information about the joint and its environs.
Some of this information can be difficult to see or inapparent using conventional (noncontrast) MRI. This data helps validate the techniques that we use to perform MR arthrography.

Vic David MD

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