EFFECT OF THE INSONIFICATION ANGLE ON THE DOPPLER BACKSCATTERED POWERUNDER RED-BLOOD-CELL AGGREGATION CONDITIONS

Citation
L. Allard et al., EFFECT OF THE INSONIFICATION ANGLE ON THE DOPPLER BACKSCATTERED POWERUNDER RED-BLOOD-CELL AGGREGATION CONDITIONS, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 43(2), 1996, pp. 211-219
Citations number
45
Categorie Soggetti
Engineering, Eletrical & Electronic",Acoustics
ISSN journal
08853010
Volume
43
Issue
2
Year of publication
1996
Pages
211 - 219
Database
ISI
SICI code
0885-3010(1996)43:2<211:EOTIAO>2.0.ZU;2-A
Abstract
It has been reported that power color Doppler ultrasound has important advantages over conventional color Doppler flow imaging, Some of thes e advantages are the aliasing free capability, the increased sensitivi ty to flow, and the angular independence. This last characteristic of power Doppler ultrasound was evaluated to verify if it was still valid in some well-defined flow conditions where porcine whole blood, calf red cells suspended in saline solution, and carbon fibers suspended in a water-glycerol mixture were used as scattering particles, Experimen ts were conducted under steady flow conditions (mean shear rates acros s the tube between 8.5 and 102 s(-1)) for insonification angles betwee n 40 and 80 degrees. Different hematocrit values (5, 10, 20, and 40%) were specifically tested for porcine whole blood. Results indicated no angular dependence for the saline suspension of calf red cells while a strong anisotropy was observed for the carbon fibers, In this last s ituation, the Doppler power in decibels increased linearly with the in sonification angle, The maximum found at 80 degrees suggests that the fibers were aligned with the direction of the flow, For porcine whole blood, an angular dependence was observed at some specific shear rate conditions, At 40% hematocrit, the anisotropy was about 5 dB for shear rates between 17 and 51 s(-1), while for a lower (8.5 s(-1)) or highe r shear rate (102 s(-1)), the anisotropy was reduced to approximately 2 dB, In all of these situations, the maximum Doppler power was observ ed for an insonification angle between 45 and 60 degrees. For hematocr it values of 5, 10, and 20%, the anisotropy was respectively on the or der of 2, 3, and 4 dB or less, depending on the shear rate conditions, Among the possible mechanisms that may explain the anisotropic effect observed in the present study, the structure of the red cell aggregat es is believed to he the determinant factor. A hypothesis concerning t he structure of the aggregates under flowing conditions in large diame ter tubes is proposed.