Frame averaging circuit for use in an ultrasound imaging system

A frame averaging circuit for use in an ultrasound imaging system, comprising

• a recursive calculation section configured to filter a blood flow velocity of a current frame to output a frame-averaged blood flow velocity based on the current frame and a previous frame;
• and
• a non-recursive section configured to determine whether to output the blood flow velocity of the current frame or to output the frame-averaged blood flow velocity calculated by the recursive calculation section, wherein the non-recursive section further comprises:
• a velocity comparator configured to compare an absolute value of the blood flow velocity of the current frame with an absolute value of the output of the recursive calculation section, wherein if the absolute value of the blood flow velocity of the current frame is larger than the absolute value of the output of the recursive calculation section, it is determined that the blood flow velocity of the current frame is larger than the previous frame, otherwise, it is determined that the blood flow velocity of the current frame is smaller than the previous frame;
• a first threshold comparator configured to compare blood flow components of the current frame and determine whether the blood flow velocity of the current frame corresponds or does not correspond to noise;
• a second threshold comparator configured to compare the blood flow velocity of the current frame with the previous frame to determine whether one or more of the following conditions occur:
• the previous frame is aliased, and
• the blood flow velocity of the current frame is flicker noise;
• a first combiner configured to combine the output of the first threshold comparator with the output of the second threshold comparator;
• a first selector configured to select whether to output the blood flow velocity of the current frame or to output the output of the recursive calculation section based on the output of the first combiner, wherein if the blood flow velocity of the current frame does not correspond to noise and one of the conditions occurs, or if the blood flow velocity of the current frame corresponds to noise, the first selector selects to output the output of the recursive calculation section, otherwise, selects to output the blood flow velocity of the current frame;
• a second selector configured to select whether to output the blood flow velocity of the current frame or to output the output of the recursive calculation section based on the output of the velocity comparator, wherein if the blood flow velocity of the current frame is larger than the previous frame, the output of the recursive calculation section is selected to be outputted, otherwise, the blood flow velocity of the current frame is selected to be outputted;
• a velocity direction determining unit configured to determine whether the blood flow velocity of the current frame is in the same direction as the previous frame;
• and
• a third selector configured to select whether to output the output of the first selector or to output the output of the second selector based on the output of the velocity direction determining unit, wherein if the blood flow velocity of the current frame is determined to be in the same direction as the previous frame, the output of the second selector is selected to be outputted, otherwise, the output of the first selector is selected to be outputted.