Final answer:
A Magnetic field is used in Magnetic Resonance Imaging (MRI). Ultrasound is the safest imaging technique during pregnancy, and X-rays were used in Compton scattering.
Step-by-step explanation:
Among the options provided, a Magnetic field is used in an MRI (Magnetic Resonance Imaging) machine. An MRI machine generates a large magnetic field around the patient to produce detailed images of the inside of the body. The magnetic field aligns the magnetization of some atomic nuclei within the body, and radio waves are used to systematically alter the alignment of this magnetization. The radio waves are absorbed and reemitted, which these emitted signals can be used to form images of the inside of the body. MRI provides good contrast between the different soft tissues of the body, which makes it especially useful in imaging the brain, muscles, heart, and cancers.
The safest imaging technique during pregnancy is an ultrasound, as it is non-invasive and does not utilize electromagnetic radiation, posing no risk to the fetus.
In Compton scattering, the type of electromagnetic radiation used was X-rays.