To determine the radiation dose to the fetus, the cumulative radiation exposure from all the radiation exams the patient receives needs to be totaled.

Potential radiation effects are proportional to the tissues exposed, either directly or indirectly by the radiation. This means a x-ray beam that includes the fetal site, or substantial scattered radiation from a site near the fetus, produces the greatest dose.3

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The following tables list mean fetal radiation exposures for single x-ray, CT, and nuclear medicine procedures at Brigham and Women's Hospital, as well as the fetal risk category as described in Table I.

Please keep in mind the following:

1. These are average doses estimated from a heterogenous range of patients.
2. Multiple exams result in an additive or cumulative dose.
3. For patient-specific dose estimates or additional information, please contact Radiology Physics (x-ray procedures) at 617-732-7201 or Health Physics and Radiopharmacology (nuclear medicine procedures) at 617-732-6057.

The radiation dose, as defined with other terms in the Glossary, may be expressed with either conventional or international (SI) units. In this guide the fetal doses are expressed in SI units.

In nuclear medicine studies, fetal radiation exposure is a function of: 1) the tracer's ability to cross the placental barrier; 2) concentrate in fetal tissue; or 3) the result of radiation emanating from a nearby organ, e.g., the urinary bladder5.

Please also note that certain radionuclides can be expressed in breast milk. Nursing mothers should consult with the nuclear medicine physician.

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* Assumes radiopharmaceutical is administered at the 3-month gestational age, while administration before or after 3 months post-conception results in a lesser fetal dose.