title: The accuracy of ultrasound volume flow measurements in the complex flow setting of a forearm vascular access.
abstract: OBJECTIVE
  Maturation of an arterio-venous fistula (AVF) frequently fails, with low post-operative fistula flow as a prognostic marker for this event. As pulsed wave Doppler (PWD) is commonly used to assess volume flow, we studied the accuracy of this measurement in the setting of a radio-cephalic AVF.
  
  
  METHODS
  As in-vivo validation of fistula flow measurements is cumbersome, we performed simulations, integrating computational fluid dynamics with an ultrasound (US) simulator. Flow in the arm was calculated, based on a patient-specific model of the arm vasculature pre and post AVF creation. Raw ultrasound signals were subsequently simulated, from which Doppler spectra were calculated in both a proximal and a distal location.
  
  
  RESULTS
  The velocity component in the direction of the PWD-US beam (vPWD), in a centered, small, sample volume, can be captured accurately using PWD spectrum mean-tracking (maximum bias [mB] 8.1%). However, when deriving flow rate from these measurements, a high degree of inaccuracy occurs. First, the angle-correction of vPWD towards the velocity along the axis of the vessel is largely influenced by the radial velocity components in the complex flow field (mB=16.3%). Second, the largest error is introduced when transferring the centerline velocity to the cross-sectional mean velocity without any knowledge of the flow profile (mB=97.7%).
  
  
  CONCLUSIONS
  In the setting of a forearm AVF, flow estimates based on PWD are hampered by the complex flow patterns. Overall, flow estimation based on centerline measurement, analyzed by mean-tracking of the RF-spectral estimates, under the assumption of a parabolic flow profile, appeared to provide the most reasonable values.
authors.affiliation: IBiTech-bioMMeda, Ghent University, Ghent - Belgium.
authors.forename: Koen
authors.initials: K
authors.lastname: Van Canneyt
authors.forename: Abigail
authors.initials: A
authors.lastname: Swillens
authors.forename: Lasse
authors.initials: L
authors.lastname: Lovstakken
authors.forename: Luca
authors.initials: L
authors.lastname: Antiga
authors.forename: Pascal
authors.initials: P
authors.lastname: Verdonck
authors.forename: Patrick
authors.initials: P
authors.lastname: Segers
mesh_terms: D001166:Arteriovenous Shunt, Surgical; D001783:Blood Flow Velocity; D016121:Brachiocephalic Veins / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*; D003198:Computer Simulation; D018619:Echocardiography, Doppler, Pulsed; D005542:Forearm / Q000098:blood supply*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D011237:Predictive Value of Tests; D017534:Radial Artery / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D013997:Time Factors; D016896:Treatment Outcome