As far as I can see it is not radioactive.
I do not see how it can become radioactive after the scan, but I am not an
expert in that area.
In any case, the half-life is only two hours and any "radioactivity" should
be pretty much gone after about six hours.
If the mother is well hydrated before and after the procedure, most of the
Isovue 300 will be in the urine and not in breast milk.
Drink a lot of fluids, urinate a lot, and breastfeed after six hours makes a
whole lot of sense if anyone is concerned despite the information below from
the NEJM.
Frank J. Nice, DPA, CPHP

See:
Iodine-Containing Contrast Medium and Antiseptic Agents
NEJM, July 13, 2000, Volume 343 (2), p. 123-124 (Drug Therapy)
"Contrast medium is not appreciably deionated.  In addition, the absorption
of hydrophilic contrast medium is minimal when it is given orally for
imaging studies of the gastrointestinal tract.  Since no toxicity is known
in full-term infants even after the DIRECT ADMINISTRATION of contrast
medium, the use of these compounds by breastfeeding women appear to pose NO
risk to their infants."

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