Which imaging technique would be least effective for visualizing deep tissue structures?

High-frequency ultrasound is often less effective for visualizing deep tissue structures due to its limitation in penetrating deeper into the body. While ultrasound is excellent for assessing superficial structures and can provide real-time imaging, high-frequency sound waves are primarily absorbed and scattered by tissues. This absorption affects their ability to visualize deeper anatomical layers, making them less ideal for examining structures located farther below the skin surface.

In contrast, techniques such as CT scans and MRI are specifically designed for imaging deeper tissues. CT scans utilize X-rays to produce detailed cross-sectional images of the body and can penetrate various tissue densities effectively, providing comprehensive views of internal structures. MRI, on the other hand, employs strong magnetic fields and radio waves to generate detailed images of soft tissues, making it superior for visualizing structures deep within the body.

Thus, while high-frequency ultrasound has its important uses in medical imaging, particularly for shallow structures, it falls short in providing adequate visualization of deeper tissues compared to the other listed imaging techniques.