What is speckle and why does it occur?

• A. Speckle is granular noise from coherent interference of echoes from tissue microstructure.
• B. Speckle is random electronic noise.
• C. Speckle arises from motion artifacts.
• D. Speckle is caused by reverberation within tissue.

Answer: (A)

Speckle is the granular texture seen in ultrasound images that comes from coherent interference of waves backscattered by many tiny tissue structures. Each microstructure within the beam’s path reflects a portion of the sound, and those reflected waves combine at the transducer with different phases. Because the imaging system detects the sum of these coherently, some regions add up constructively and others destructively, producing bright and dark speckle grains. This pattern is a fundamental signal effect of coherent imaging, not random electronic noise. It isn’t primarily due to motion artifacts (which smear patterns) or reverberation (which creates distinct repeated echoes from strong interfaces). The speckle size roughly matches the image’s resolution cell and depends on wavelength and aperture, so higher frequencies yield finer speckle. Techniques like averaging or speckle-reduction filters can soften it when needed, while still recognizing that speckle carries texture information about the tissue.