G S Lin1, V S Naval. 1. Advanced Imaging Associates, Fremont, CA 94555-2016, USA.
Abstract
OBJECTIVE: To visualize the spatial variation of Doppler indices, principally the pulsatility index, taken proximal to the carotid bifurcation and to evaluate their relationship to the geometry of the carotid bulb. METHODS: The pattern of ultrasonographic Doppler indices was studied in healthy volunteers by using hemodynamic color Doppler imaging, which computes and displays a Doppler index at each color pixel from a sequence of color Doppler image frames taken over several cardiac cycles. RESULTS: In carotid bulbs with laminar flow (n = 5), the spatial partitioning between low-resistance internal carotid artery and high-resistance external carotid artery flows could be followed over 5 cm upstream in the common carotid artery. However, normal reverse or vortex flows at the carotid bulb (n = 15) obliterated upstream flow partitioning within 2 cm of the flow divider The pulsatility index was neither laterally nor axially uniform in the common carotid artery. CONCLUSIONS: Localization of "core flow" where meaningful Doppler indices may be measured is determined by the expansion geometry of the carotid bulb and usually requires positioning of a small sample volume in the center of the lumen at least 3 cm upstream from the flow divider However, in the absence of reverse or vortex flows, placement of a spectral Doppler sample volume is best guided by hemodynamic color Doppler imaging.
OBJECTIVE: To visualize the spatial variation of Doppler indices, principally the pulsatility index, taken proximal to the carotid bifurcation and to evaluate their relationship to the geometry of the carotid bulb. METHODS: The pattern of ultrasonographic Doppler indices was studied in healthy volunteers by using hemodynamic color Doppler imaging, which computes and displays a Doppler index at each color pixel from a sequence of color Doppler image frames taken over several cardiac cycles. RESULTS: In carotid bulbs with laminar flow (n = 5), the spatial partitioning between low-resistance internal carotid artery and high-resistance external carotid artery flows could be followed over 5 cm upstream in the common carotid artery. However, normal reverse or vortex flows at the carotid bulb (n = 15) obliterated upstream flow partitioning within 2 cm of the flow divider The pulsatility index was neither laterally nor axially uniform in the common carotid artery. CONCLUSIONS: Localization of "core flow" where meaningful Doppler indices may be measured is determined by the expansion geometry of the carotid bulb and usually requires positioning of a small sample volume in the center of the lumen at least 3 cm upstream from the flow divider However, in the absence of reverse or vortex flows, placement of a spectral Doppler sample volume is best guided by hemodynamic color Doppler imaging.