Advancements in Noncontrast Ultrasound Imaging for Low-Velocity Flow: A Technical Review and Clinical Applications in Vascular Medicine.

Visualizing the arterial tree using ultrasound, from the aorta to the small vessels, has significantly improved over time due to advances in ultrasound imaging technology. Initially limited to exploring the major vessels, ultrasound analysis has made considerable progress with enhanced image quality. While injecting microbubbles as a contrast agent partially addresses this limitation, its use is constrained by the need for intravenous injection, making the examination more complex and time-consuming. To address these drawbacks, new commercial modes have emerged, distinct from conventional color- and power-Doppler modes, offering the ability to analyze slow flows and, consequently, microvascularization. These dedicated imaging modes include B-flowTM, E-flowTM, Superb Microvascular Imaging (SMITM), Micro Flow Imaging (MFITM), MV-FlowTM, Detective Flow Imaging (DFITM), Micro-VTM, and Angio PLUS imagingTM. Although these modes share similar objectives, they are based on different technologies, each with its own specific characteristics. The exact algorithms behind these modes vary and are proprietary but rely on a combination of approaches to reduce tissue clutter and electronic noise while improving sensitivity to slower-flow Doppler signals. This review aims to explain the technological basis of these "microvascular flow imaging modes" (MVFI) currently clinically available in vascular imaging to the physician and sonographer specialized in vascular ultrasound, discussing their current limitations and potential applications in vascular medicine.