Final answer:
MRI is the safest imaging study to use during pregnancy as it does not involve radiation exposure.
Step-by-step explanation:
Magnetic Resonance Imaging (MRI) is the imaging study that can be used most safely during pregnancy. Unlike CT scans and PET scans, MRI does not involve radiation exposure, making it a safer option for pregnant women. MRI uses radio waves and magnetic fields to produce detailed images of the body, without any known risks to the developing fetus.