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PubMed1992

Experimental studies to define the geometry of the flow convergence region. Laser Doppler particle tracking and color Doppler imaging.

The color flow convergence method for calculating volume flow through regurgitant or forward flow restrictive orifices has gained significant interest and a number of in vitro studies have suggested that this method is accurate, even in pulsatile models. Clinical application of the method over a wide range of conditions will require improved understanding of the effect of orifice size, flow geometry, and flow rate on the flow convergence geometry. In this study, we performed laser particle tracking investigations to allow visualization of streamlines into stenotic orifices. These streamlines are theoretically perpendicular to the isovelocity surfaces used for flow convergence calculations. We compared those observations to color flow map, flow convergence images obtained with a Toshiba 160A for orifices 5 to 15 mm 2 with flow rates of 1.5 to 9.7 L/min. Our results show that for large orifices, low flow rates, and/or low pressure gradients, more oblique streamlines in the velocity of the orifice correspond to nonhemispherical, but more elliptical, flow convergence geometries. This can be corrected for by using lower Nyquist limits and calculating flow convergence at greater distances from the orifice. Under high flow and high gradient conditions, increased Nyquist limits and shorter aliasing radii are more suitable. Our studies yield insights into flow convergence geometry and yield corrective procedures to improve volume flow calculation.

Blood Flow Velocity↗
PubMed1998

[Discrepancies between the results of phlebography and Doppler ultrasonography in the diagnosis of asymptotic venous thrombosis after total hip prosthesis. False negatives of phlebography or false positives of Doppler ultrasonography].

OBJECTIVES: Assess the diagnostic performance of phlebography and discrepancies with duplex ultrasonography in screening for asymptomatic deep vein thrombosis after total hip arthroplasty. Search for arguments which would favor contributing false-negatives or false-positives to one of the two exploration methods. PATIENTS AND METHODS: The study included 24 patients who underwent the 2 explorations independently between day 7 and day 14 in a multicentric therapeutic trial of a new heparin. Discrepancies between the two techniques were recorded. Diagnostic performance of phlebography was calculated from contingency tables. The phlebograms were then reviewed with knowledge of the duplex ultrasonographic findings. The course of the venous thrombus after treatment was monitored with duplex ultrasonography. RESULTS: Phlebography allowed the diagnosis of thrombus formation in 9 patients. Ultrasonography provided the diagnosis in 14 cases out of 24. Sensitivity of phlebography compared with duplex ultrasonography was 64% (95% CI = 35.1-87.2) (9/14) and specificity was 100% (95% CI = 69.1-100) (10/10). Several localizations were not visualized with phlebography: 3 partially obstructive thrombi near the femoral junction, and 38 distal thrombi including 31 soleus thrombi (fig. 5). When the phlebograms were reviewed again, defects compatible with a partial thrombus were found for the 3 proximal localizations and for 2 of the distal localizations (fig. 1, 2, 4). None of the soleus localizations were visualized. Duplex ultrasonographic follow-up concerned 12 of the 14 patients with a thrombus identified by duplex ultrasonography involving 44 localizations. In five case, the operator was different from the operator for the initial duplex ultrasonography. Follow-up revealed: 1 new localization, 37 narrowings and 6 repermeabilizations. DISCUSSION: The coherence of the duplex ultrasonographic follow-up and the presence of images compatible with partial thrombus on the revised phlebograms which had been initially interpreted as wash out flow constitute a group of arguments suggesting that the discrepancies observed should be considered as phlebography false-negatives. This defect in the sensitivity of phlebography has been reported by others in the literature both for distal and proximal localizations.

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