Frame persistence (temporal averaging) affects speckle and motion perception how?

• A. Increases frame rate without affecting speckle
• B. Has no effect on speckle or motion
• C. Decreases SNR and increases speckle but improves motion perception
• D. Increases SNR and reduces speckle but can blur fast motion and reduce temporal resolution

Answer: (D)

Frame persistence uses temporal averaging of successive frames. By combining multiple frames, random noise tends to cancel while the true signal adds, so the signal-to-noise ratio improves. The speckle pattern in ultrasound arises from coherent interference of backscattered waves; averaging over time smooths out these random speckle fluctuations, making speckle appear reduced. The trade-off is that any moving structures will be blurred during the averaging window, so fast motion becomes smeared and temporal details are lost. In short, temporal averaging increases SNR and reduces speckle, but can blur fast motion and lower temporal resolution.