Relative blood flow changes measured using calibrated frequency-weighted Doppler power at different hematocrit levels.
In theory, the power of a trans-cranial Doppler signal may be used to measure changes in blood flow and vessel diameter in addition to velocity. In this study, a flow index (FI) of relative changes in blood flow was derived from frequency-weighted Doppler power signals. The FI, plotted against velocity, was calibrated to the zero intercept with absent flow to reduce the effects of non-uniform vessel insonation. An area index was also calculated. FIs were compared with actual flow in four silicone tubes of different diameter at increasing flow rates and increasing hematocrit (Hct) in a closed-loop phantom model. FI values were strongly correlated with actual flow, at constant Hct, but varied substantially with changes in Hct. Percentage changes in area indexes, relative to the 4-mm tube, were strongly correlated with tube cross-sectional area. The implications of these results for in vivo use are discussed.
Department of Neurology, Oslo University Hospital, Rikshospitalet, Oslo, Norway. Electronic address: seanwallace@live.no.
Sean
S
Wallace
Department of Neurology, Haukeland University Hospital, Bergen, Norway.
Nicola
N
Logallo
Department of Neurology, Akershus University Hospital, Oslo, Norway.
Kashif W
KW
Faiz
Department of Neurology, Oslo University Hospital, Rikshospitalet, Oslo, Norway.
Christian
C
Lund
Department of Medical Engineering, University of Applied Sciences, Ulm, Germany.
Rainer
R
Brucher
Department of Neurology, Oslo University Hospital, Rikshospitalet, Oslo, Norway.
David
D
Russell
D000465:Algorithms; D001783:Blood Flow Velocity / Q000502:physiology; D001921:Brain / Q000502:physiology; D002138:Calibration; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006400:Hematocrit / Q000379:methods* / Q000592:standards*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods* / Q000592:standards; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D017585:Ultrasonography, Doppler, Transcranial / Q000295:instrumentation / Q000379:methods* / Q000592:standards*
Area index; Doppler power; Flow index; Hematocrit; Trans-cranial Doppler