What causes the speckle pattern seen in ultrasound images?

• A. Coherent interference of echoes from tissue microstructure
• B. Random electronic noise
• C. Motion artifacts
• D. Shadowing

Answer: (A)

Speckle is produced by the coherent interference of echoes from many tiny tissue scatterers within each ultrasound resolution cell. Each microstructure reflects part of the incident wave with its own phase and amplitude, and the receiver sums all these echoes. Because the phases are different, some echoes add up constructively in bright spots and destructively in dark spots, creating a granular, seemingly random texture—the speckle pattern. The pattern reflects the random arrangement of scatterers in tissue and can change with scanning angle or frequency. This differs from random electronic noise, motion artifacts, or shadowing, which have different origins and do not produce the characteristic tissue-like speckle texture.