Answer to Question #12776 Submitted to "Ask the Experts"

Could you tell me what radionuclide might have been used on me when I had a lung scan after a caesarean section in 1989?

The day after the birth, I was short of breath. I know they injected a radiopharmaceutical drug and then I was sitting up and the machine scanned the front of my chest. I do not recall inhaling anything through a mask (like I read on some of the descriptions on your website). 

This was almost 30 years ago and the hospital no longer exists. 

After this test no one told me not to breast-feed. My daughter, who was a newborn at the time, is now diagnosed with connective tissue disorder and has low white blood cell and platelet counts. She also has had fibrous breasts and numerous ultrasounds for this condition. I am hoping to at least be able to tell the doctors who are treating her what she was exposed to as a newborn. I am hoping this will help in their treatment plan for her.

Pregnant women who are near term, or who have just given birth, are at increased risk for blood clots forming in their legs. Some of these clots may break apart and lodge in the lungs, causing a so-called pulmonary embolism (PE). An early symptom of PE is shortness of breath. Because a PE can be fatal, it must be quickly ruled in or out. 

My guess is that you were having some shortness of breath and someone noticed it. The safest way to rule out a PE is with a "ventilation-perfusion lung scan," also called a "V/Q" scan. This was true in 1989 and is still true today, and the procedure has not changed much. 

First, a very small amount of a radioactive form of aggregated human serum albumin (a protein normally found in the blood) is injected into a vein and pictures of the lungs are taken from the back, front, and sides of the chest. That’s the "perfusion" part of the scan and is intended to see if the blood supply to parts of the lungs has been blocked by a clot. 

If the pictures show evidence of a clot, then the "ventilation" part of the scan is performed. That involves breathing a small amount of radioactive gas through a mask and repeating the pictures. Since you don't recall inhaling anything, my thinking is that the "perfusion" part of your scan showed no evidence of a clot, and the "ventilation" part was not needed. 

This is a common result. Fortunately, few cases of shortness of breath around the time of delivery are due to PE.

You've discovered that some nuclear medicine drugs can get into breast milk after they are administered to the mother and may be consumed by the baby unless nursing is interrupted. In the 1950s and 1960s the human serum albumin was "tagged" with a radioactive form of iodine (¹³¹I). Because ¹³¹I has a long half-life (eight days), is readily secreted in breast milk, and will accumulate in the baby's thyroid gland, it's not appropriate to use it in scanning during nursing. 

However, by 1989 the use of ¹³¹I for V/Q scans would have been entirely replaced by the use of another tag (^99mTc). This tag was highly favored because it has a much shorter half-life (six hours) and does not accumulate in the thyroid gland as much as ¹³¹I. 

I am pretty certain ^99mTc was used for your scan. In 1989 there wasn't a lot of guidance about how long to tell a patient to interrupt nursing after a ^99mTc V/Q scan. Today, we would tell you to interrupt nursing for a few hours after the scan, and that even if nursing was not interrupted, there would be no significant radiation risk to your baby.

Robert E. Reiman, MSPH, MD 
Associate Professor of Radiology