Question

Ultrasound and Magnetic Resonance Imaging (MRI), are technologies used to create images of a patient's internal features. In many instances, either technology can be used when diagnosing patients. However, ultrasound is often preferred for diagnosing moving features, while MRI is often preferred for diagnosing features surrounded by air or dense bone. Based on these differences, which of the following best describes the waves used by these technologies?
A.
Ultrasound uses sonar technology with sound waves, while MRI uses electromagnetic waves.
B.
Ultrasound and MRI both use electromagnetic waves because electromagnetic waves require a medium through which to travel.
C.
Ultrasound uses electromagnetic waves, while MRI uses sonar technology with sound waves.
D.
Ultrasound and MRI both use sonar technology with sound waves because sound waves are not affected by a change in medium.

Answer 1

A.

Ultrasound uses mechanical (sound) waves—pulse/echo sonar-like pressure waves—whereas MRI uses electromagnetic (radiofrequency) waves in combination with strong magnetic fields to excite and detect proton spins. The other choices are incorrect about which modality uses sound vs. EM waves and about the properties of EM vs. sound waves.