The optimal time delays used during receive focusing change depending upon the ______ at which the reflection was created.

The optimal time delays used during receive focusing change depending upon the ______ at which the reflection was created.

• A. Depth
• B. Angle
• C. Frequency
• D. Speed of sound

Answer: (A)

In receive focusing, the array applies time delays to each element so that echoes coming from a specific focal point arrive in phase when they’re summed. The needed delays come from geometry: each element is a different distance from the reflection, so the travel time to and from the reflector differs across the array. As the reflection depth increases, those distance differences change, requiring a different set of delays to keep the signals aligned. Therefore, the optimal receive delays depend on the depth of the reflection—the deeper the point, the particular delay pattern that will best focus at that depth. The speed of sound in tissue is used to convert distance into time, but the controlling factor for the delays themselves is the depth. Frequency or incidence angle influences other imaging aspects, but they don’t set the depth-based delay pattern for receive focusing.

In receive focusing, the array applies time delays to each element so that echoes coming from a specific focal point arrive in phase when they’re summed. The needed delays come from geometry: each element is a different distance from the reflection, so the travel time to and from the reflector differs across the array. As the reflection depth increases, those distance differences change, requiring a different set of delays to keep the signals aligned. Therefore, the optimal receive delays depend on the depth of the reflection—the deeper the point, the particular delay pattern that will best focus at that depth. The speed of sound in tissue is used to convert distance into time, but the controlling factor for the delays themselves is the depth. Frequency or incidence angle influences other imaging aspects, but they don’t set the depth-based delay pattern for receive focusing.