Quantification of cerebral perfusion with "real-time" contrast-enhanced ultrasound

Background - No noninvasive technique is currently capable of "real-time" assessment and monitoring of cerebral blood flow (CBF). We hypothesized that cerebral perfusion could be accurately measured and monitored in "real time" with contrast-enhanced ultrasound (CEU). Methods and Results - Cerebral perfusion was assessed in 9 dogs through a craniotomy with CEU at baseline and during hypercapnia and hypocapnia while normoxia was maintained. Cerebral microvascular blood volume (A), microbubble velocity (β), and blood flow (A×β) were calculated from time-versus-acoustic intensity relations. Compared with baseline, hypercapnia and hypocapnia significantly increased and decreased CBF, respectively, as measured by CEU. These changes in blood flow were mediated by changes in both A and β. A good correlation was found between A×β derived from CEU and CBF measured by radiolabeled microspheres (y=0.67x-0.04, r=0.91, P<0.001). Conclusions - Changes in both cerebral microvascular blood volume and red blood cell velocity can be accurately assessed with CEU. Thus, CEU has the potential for bedside measurement and monitoring of cerebral perfusion in real time in patients with craniotomies or burr holes.