Which imaging mode provides real-time visualization of structures?

B-mode, or Brightness mode, is the correct choice because it is specifically designed to display two-dimensional images of internal structures in real-time. In this mode, varying intensities of echoes returning from tissues are displayed as different shades of gray on the screen, allowing for the visualization of anatomical structures in a detailed manner. This capability is essential in dynamic assessments of structures, such as organs and blood flow, making it a fundamental choice in diagnostic ultrasound.

Cine mode, while also capable of showing motion, typically refers to the ability to capture a sequence of images over time for review, rather than providing continuous real-time visualization. M-mode primarily records motion along a single line of sight, which is helpful for assessing movement in a specific area but does not provide a comprehensive two-dimensional view. Duplex mode combines B-mode and Doppler ultrasound to provide both structural images and flow information, but it is not solely focused on real-time imaging like B-mode; rather, it integrates Doppler information, which may not be continuous.

Hence, B-mode stands out as the primary imaging mode for real-time visualization of anatomical structures in ultrasonography.