Which statement best differentiates A-mode from B-mode imaging and includes a typical clinical application for each?

• A. A-mode provides two-dimensional grayscale cross-sections; B-mode provides one-dimensional depth plots.
• B. A-mode is a one-dimensional plot of echo amplitude versus depth, and B-mode provides two-dimensional grayscale cross-sections for anatomy.
• C. A-mode uses color Doppler; B-mode uses spectral Doppler.
• D. A-mode and B-mode are identical imaging modalities.

Answer: (B)

A-mode versus B-mode imaging is defined by how echoes are converted into information: A-mode yields a one-dimensional plot of echo amplitude versus depth, while B-mode creates two-dimensional grayscale images of anatomy. In A-mode, you see spikes along a single depth axis that tell you exactly how deep each reflector is, which is useful for precise depth measurements such as ocular axial length. In B-mode, those echoes are displayed as brightness along both the vertical depth and a horizontal axis, producing a cross-sectional view of structures and organs—the standard way to visualize anatomy in ultrasound.

This distinction is why the statement is best: it correctly identifies the one-dimensional depth plot for A-mode and the two-dimensional grayscale cross-section for B-mode, and it aligns each mode with its typical clinical use. Doppler techniques (color or spectral) are separate tools and do not define A- or B-mode imaging.