This is from dr newman...
X-rays and scans. Ordinary X-rays do not require a mother to interrupt breastfeeding even when used with contrast material (example, intravenous pyelogram). The reason is that the material does not get into the milk, and even if it did it would not be absorbed by the baby. The same is true for CT scans and MRI scans. You do not have to stop for even a second.
What About Radioactive Scans?
We do not want babies to get radioactivity, but we rarely hesitate to do radioactive scans on them. When a mother gets a lung scan, or lymphangiogram with radioactive material, or a bone scan, it is usually done with technetium (though other materials are possible). Technetium has a half life (the length of time it takes for ½ of all the drug to leave the body) of 6 hours, which means that after 5 half lives it will be gone from the mother’s body. Thus, 30 hours after injection all of it will be gone (well 98% will be gone) and the mother can breastfeed her baby without concern about his getting radiation. But does all the radioactivity need be gone? After 12 hours, 75% of the technetium is gone, and the concentration in the milk very low. I think that waiting 2 half lives is enough, for a material such as technetium. But: Not all technetium scans require stopping breastfeeding at all (HIDA scan, for example). It depends on which molecule the technetium is attached to. In the first few days, there is very little milk (though there is enough). In this situation it would be unnecessary for the mother to stop breastfeeding after a lung scan, for example. However, one of the most common reasons to do a lung scan is to diagnose a clot in the lung. This can now be done better and faster with CT scan, which does not require interrupting breastfeeding for even 1 second.
If you decide that interruption of breastfeeding is the best course to follow, then express milk for several days in advance (if you have advance warning about the test) and this can be fed via cup for a few days. Then while not breastfeeding, express your milk but don’t throw away the milk. The radioactive tracer that is present in the milk decays and the radiation is gone in 5 half-lives. So, even for I¹³¹ used in thyroid scans (see below), the radioactivity of the iodine will be gone in 5 half-lives, so the milk can be used in 6 to 8 weeks (the half-life of I¹³¹ is about 8 days). Only occasionally is a radioactive scan so urgent that it cannot be delayed for a few days.
Thyroid scans are different. Radioactive iodine (I¹³¹) is concentrated in milk and will be ingested by the baby and it will go to his thyroid where it will stay for a long time. This is definitely of concern. So, the mother will have to stop breastfeeding? No, because often the test does not need to be done at all. Differentiating postpartum thyroiditis from Graves’ Disease (the most common reason for doing the scan in breastfeeding mothers) does not require a thyroid scan. Get more information from the clinic. If a scan needs to be done, it is possible to do a thyroid scan I¹²³ which requires stopping for only 12 to 24 hours, depending on the dose given or technetium (see above). Don’t forget to express milk in advance so the baby can get it instead of formula.