Sorry, the nurses have got it backwards.  When, for once, you have a
progressive radiology department where they understand that the dye from
a CT scan is virtually completely inoffensive, and won't get into the
milk in any substantial quantities anyways, and even if it did it would
not be absorbed by the baby, they ask for proof.  Why don't they want
mothers to breastfeed?  Hale discusses contrast media very nicely.  And
I would think that no more documentation is necessary.

As for lung scan, I would not say 24 hours either.  It depends on the
situation.  After all, if we are talking immediate postpartum period,
then the amount of milk the baby will get is small (but normal).  Thus
the amount of radioactive dye he will get is minimal.  Furthermore, we
do radioactive scans on babies and we seem to think that is alright.
The half life of technetium is about 6 hours, which means that in six
hours half of it is gone from the mother's body and the blood levels
(and thus milk levels) would be very much lower.  I think, 6 to 12 hours
is more than adequate to hold off.  24 hours if you want to be sure the
baby gets almost none.

Jack Newman, MD, FRCPC