Identify the primary function of ultrasound in medical imaging.

The primary function of ultrasound in medical imaging is to visualize soft tissues and structures using high-frequency sound waves. This technique employs sound waves that are emitted by a transducer, which then reflects off tissues and structures in the body. The reflected sound waves are captured by the transducer and converted into real-time images displayed on a monitor.

Ultrasound is particularly effective for imaging soft tissue organs such as the heart, liver, kidneys, and developing fetus during pregnancy. Its non-invasive nature, lack of ionizing radiation, and ability to provide dynamic images make it an invaluable tool in many medical situations.

Other techniques mentioned in the options, like creating detailed images of bones and joints, involve different imaging modalities such as X-rays or MRI, which are better suited for hard tissues. Analyzing blood flow typically relies on Doppler ultrasound, which is a specialized application of the basic ultrasound principle rather than its primary function. Measuring radiation levels is outside the scope of ultrasound, as radiation is more relevant to modalities like X-ray and CT imaging.