Blooming or color bleed artifact occurs when the color signal indicating blood flow extends beyond its true boundaries, spreading into adjacent regions with no actual flow.
This artifact mainly affects the portion of the image distal to the vessel and the transducers. It is somewhat similar to its MRI namesake as both phenomena denote something that seemingly appears larger than its true physical limits.
Blooming occurs because the spatial resolution of color Doppler is lower than greyscale ultrasound 1. It can be exaggerated by inappropriately high color gain.
It is important to be aware of as it may obscure partial occlusions such as thrombi resulting in misdiagnosis 2. It can be avoided by lowering the color gain until the bleed of signal outside of the vessel disappears 3.