Which imaging modality uses high-frequency sound waves?

The correct choice is ultrasound, as this imaging modality specifically utilizes high-frequency sound waves to create images of structures within the body. Unlike other imaging techniques that rely on ionizing radiation (like X-rays and CT scans), ultrasound employs sound waves that are emitted from a transducer. These sound waves travel through body tissues and reflect back to the transducer, which then converts the echoes into real-time images. This method is particularly useful for visualizing soft tissues and is commonly used in obstetrics, cardiology, and various diagnostic evaluations.

In contrast, X-ray, MRI, and CT utilize different principles for imaging: X-ray uses ionizing radiation to create images based on the differential absorption of x-rays by various tissues; MRI employs strong magnetic fields and radio waves to produce detailed images of organs and tissues; and CT, similar to X-ray, also uses ionizing radiation but provides cross-sectional images of the body. Each of these modalities has its unique applications and limitations, but they do not utilize high-frequency sound waves like ultrasound does.