Which imaging mode yields a two-dimensional grayscale image representing reflectivity versus depth?

• A. Doppler measurement
• B. Two-dimensional grayscale
• C. One-dimensional
• D. Color-coded flow

Answer: (B)

Two-dimensional grayscale imaging, often called brightness mode, is designed to display tissue reflectivity as brightness across a scanned plane. Echoes from different depths are mapped to vertical positions, while scanning across the width builds the second horizontal axis. The brightness of each pixel represents the strength of the echo from that point, giving a real-time cross-sectional image of anatomy in grayscale. Doppler measurement focuses on motion or velocity of moving structures and is shown as velocity information (often color-coded or in spectra), not a pure grayscale reflectivity map. One-dimensional imaging (A-mode) shows echo amplitude versus depth along a single line, producing spikes instead of a 2D image. Color-coded flow adds Doppler information to a grayscale image, but the primary grayscale image itself is not a 2D reflectivity map alone.