Ultrasonic Quantitative Flow Volumetry of the Carotid Arteries: Initial Experience with a Color Flow M-Mode System

Noninvasive hemodynamic testing of the cerebral vessels has been limited to the use of flow velocity rather than potentially more powerful parameters such as volume flow rate. Color velocity imaging (CVI), a time-domain based color flow imaging method, offers potential for volume flow rate determination. This technique uses a color M-mode function for simultaneous determination of flow velocity and functional vessel diameter. As flow volume (m(3) x s(-1)) is the product of flow velocity (m x s(-1)) and area (m(2)) where this velocity occurs, these data are integrated to determine the effective flow volume. Before applying this new technique on clinical patients we tested the system in an in vitro setting and on normal volunteers. (1) In vitro flow volume tests on a computer-controlled flow phantom proved to be accurate for all constant flow volumes in a range of 120-1,040 ml/min and pulsatile flow volumes from 70 to 360 ml/min. (2) A major concern before utilizing this technique in daily practice is the question of in vivo intra- and interoperator variability. We found the interoperator variability overall negligible. Intraoperator variability is acceptable when at least three samples are obtained per site. (3)In a pilot study we performed an age-, gender- and race-matched community nomogram trial. Technically acceptable data could be obtained from almost all common carotids (97%), 71% of all internal carotids and 53% of all vertebrals arteries. We found a significant (p < 0.0001) difference of volume flow rate depending on gender, with men having a 15% higher flow volume. A less striking correlation (p < 0.001) was found for an inverse relationship of age and volume flow rate. All other tested parameters (blood pressure, heart rate, race, level of education, smoking, weight, body surface) proved to be insignificant. In summary, ultrasonic flow volumetry with CVI-Q is a feasible method, which promises to be an exciting tool in the assessment of cerebral hemodynamics. Future studies will focus on the impact of carotid stenosis on volume flow rate and on clinical disorders like dementia, cardiac insuffiency or migraine.