<p>Color and power Doppler imaging has been employed for decades to analyze the presence, amount, and distribution of flow signals (i.e., blood vessels) in organs and abnormalities, representing a valuable adjunct to gray-scale morphostructural ultrasound. Conventional Doppler modalities, however, have the significant limitation of being insensitive to detect flow within vessels that are too thin and/or that contain blood flowing too slow. In this review article, we focus on the systems that the different companies have developed in the last decade to improve the ultrasound effectiveness in sensitively detecting microvascular flows.</p>