A BC-mode image with an improved frame rate in an ultrasound system is formed. A transmit/receive unit forms first and second receive signals responsive to first and second control signals. An image processing unit is configured to form a B-mode image and a C-mode image based the first and second receive signals and to combine them to form a BC-mode image. The control signal generates a third control signal for a B-mode scan along scan lines, which are not within the color box to form third receive signals. The control unit repeatedly generates the second and third control signals. The image processing unit is further operable to form a B-mode image based on the third receive signals and the second signals.
