Intraoperative cerebral angiosonography with ultrasound contrast agents: how I do it

Background: Intraoperative vessel visualization is highly desirable, especially when the target is related to or close to main vessels, such as in the skull base and vascular surgery. Contrast-enhanced ultrasound (CEUS) is an imaging technique that allows visualization of tissue perfusion and vascularization through the infusion of purely intravascular ultrasound contrast agents (UCA). Methods: After cerebral scanning with B-mode ultrasound (US) CEUS is performed, UCA are injected and insonated with low mechanical index US. A UCA-specific harmonic signal is transduced using a contrast-specific algorithm to obtain real-time angiosonography (ASG). Conclusions: Real-time intraoperative ASG is a rapid, reliable, repeatable method for vessel visualization and evaluation of tissue perfusion. Key points: • ASG permits to assess vessel position, dimension, and relationships; it also allows a qualitative evaluation of flow entity and direction. • ASG shows vessels in depth without the need of their direct exposure, as for fluorescence-guided surgery. • ASG permits to study the entire vascular tree without the necessity to set gain or pulse repetition frequency as in Doppler imaging. • Vessels of interest can be visualized following their entire length across the surgical field, along the arterial, capillary, and venous districts. • ASG scan is repeatable multiple times throughout the operation, and each exam could be recorded as a clip to be visualized at a later stage. • In case of neoplastic lesion, ASG characterizes the perfusion pattern in three phases: arterial, venous, and parenchymal, permitting to visualize afferent and efferent vessels, facilitating the surgical strategy. • During tumor debulking, ASG shows the remaining distance to major vessels, providing information to avoid direct vessel damage. • In tumor and AVM surgery, ASG shows nidus or tumoral remnants that might be covered by healthy tissue, thus not visible on the surface. • In case of aneurysm surgery, post-clipping angiosonographic control confirms proper aneurysm exclusion and distal vessels flow.