A pregnant woman develops progressive dyspnea and tachypnea after a period of prolonged bed rest.  Give the expected radiation dose to the fetus for various studies utilized in the workup of pulmonary embolism.  

External shielding during CT?

The decision on whether to shield the uterus during CT must weigh the expected exposure from internal scatter against the expected external exposure from tube-housing and collimeter leakage.  Unlike external sources of radiation, internal scatter would not be affected by the use of external shielding; instead, one theorectial concern is for back scatter off the lead apron itself and thus redirection of radiation towards the fetus.