SMI is an acronym for Superb Microvascular Imaging.
SMI is a Doppler technique from Canon. SMI uses new algorithms to remove clutter from the Doppler signal and enhance the amplitude of the echoes from the flowing blood. This enables SMI to image smaller vessels and vessels that have slower flow. This sounds similar to Power Doppler. However, in a small recent study, SMI was seen to be more sensitive than Power Doppler to detecting slow flow in small vessels.
Toshiba's SMI Doppler imaging of a small liver HCC