Color Doppler imaging (CDI) is a sophisticated form of ultrasound technology that overlays blood flow and velocity information onto a B-mode, two-dimensional, gray-scale image. This imaging technique--also called color Doppler echocardiography, color-coded Doppler, Doppler color-flow imaging, and color-flow imaging--is a type of pulsed-wave Doppler echocardiography. Because the anatomical site of received Doppler-shift information can be readily determined, CDI is useful for documenting normal blood flow patterns and screening the heart and great vessels for areas of abnormal flow.