Direct quantification of mitral regurgitant flow volume by real-time three-dimensional echocardiography using dealiasing of color Doppler flow at the vena contracta.
ABSTRACT Real-time 3-dimensional color Doppler echocardiographic (RT3DE) imaging has recently been demonstrated to provide accurate direct measurement of vena contracta area (VCA). The quantification of mitral regurgitant (MR) flow directly at the lesion using color Doppler echocardiography, however, has been prevented because of multiple aliasing from high flow velocities. Recent studies, however, have demonstrated that flow at the vena contracta is laminar, with a narrow velocity spectrum that should allow the dealiasing of color Doppler flow velocities for the accurate measurement of MR flow. This hypothesis was tested in an in vitro flow model and initial patient application, with magnetic resonance imaging (MRI) used as a reference.
In an in vitro flow model, MR jets of flow rates from 5 to 60 mL/s were produced through asymmetric orifices of 0.2 to 0.6 cm(2). From RT3DE data sets, MR flow was calculated by the automated integration of the nonaliased color Doppler velocities over the VCA, with aliasing avoided by maximum baseline shift. Aliased flow was calculated as VCA times the Nyquist velocity times the number of aliasing transitions derived from the maximum continuous-wave Doppler velocity. Total MR flow was calculated as the sum of nonaliased and aliased flow. This approach was also clinically evaluated in 23 patients for the measurement of MR stroke volume against MRI and the hemispheric and hemielliptic proximal isovelocity surface area methods.
In vitro RT3DE imaging of VCA was feasible in all flow stages without color Doppler aliasing. Flow rates calculated from RT3DE data sets showed excellent correlation with actual flow rates (r = 0.99), with a mean difference of -0.05 +/- 0.5 mL/s (not significant by t test). In vivo, good correlation and agreement were found between MR stroke volume by dealiasing and MRI (r = 0.91, -1.8 +/- 7.1 mL; not significant by t test), with better correlation and agreement compared with hemispheric proximal isovelocity surface area (r = 0.81, -17.4 +/- 9.4 mL, P < .05) and hemielliptic proximal isovelocity surface area (r = 0.89, -11.7 +/- 7.4 mL, P < .05).
Dealiasing of color Doppler flow at the vena contracta is feasible and appears promising for measuring MR severity quantitatively. This novel approach can be readily implemented in current systems to provide rapid semiautomated MR flow volume and MR fraction.
[show abstract] [hide abstract]
ABSTRACT: Color Doppler jet area (CDJA) is an important measure used to classify mitral regurgitation (MR) severity. The investigators hypothesized that the presence and configuration of multiple regurgitant jets can alter CDJA quantification for fixed regurgitant volumes. This has relevance to MR assessment prior to the treatment of valves with multiple regurgitant orifices or after surgical or percutaneous double-orifice mitral valve repair. An in vitro model was developed to create jets flowing through a simulated mitral orifice into an imaging chamber. The flow loop was driven with a pulsatile pump at 60 beats/min containing a water-glycerol solution approximating the viscosity of blood. At the orifice, simulated regurgitant stroke volumes of 2.5 to 25 mL were created through plates having either single openings with orifice areas from 0.125 to 0.50 cm(2) or two to four openings with total orifice area of 0.25 cm(2) and varied linear spacing. An 8-MHz transthoracic two-dimensional ultrasound probe was used to acquire jet velocities by continuous-wave Doppler as well as color Doppler for offline analysis. CDJA values were obtained with custom automated pixel-counting software. Peak jet velocities ranged from 30 to 550 cm/sec. For single jets, normalized average CDJA values increased nonlinearly as a function of average Reynolds number. Peak CDJA values were up to 62% higher for multiple jets compared with single jets with similar total orifice areas and simulated regurgitant stroke volumes. The presence or absence of multiple jets, rather than the total number of jets, appeared to have a greater effect on maximum CDJA. In addition, peak CDJA values for multiple jets increased with increased linear spacing. A fixed regurgitant volume involving multiple jets will have a larger CDJA value than the same total volume from a single jet. The source of this discrepancy appears to be increased ambient fluid entrainment from adjacent regurgitant jets. This potential overestimation of MR severity using color Doppler flow jets should be taken into consideration when assessing MR prior to treatment or when assessing residual MR after double-orifice mitral valve repair.Journal of the American Society of Echocardiography: official publication of the American Society of Echocardiography 09/2010; 23(9):993-1000. · 2.98 Impact Factor
Article: A Three-Dimensional Computational Fluid Dynamics Model of Regurgitant Mitral Valve Flow: Validation Against in vitro Standards and 3D Color Doppler Methods.Cardiovascular Engineering and Technology 06/2011; 2(2):77-89.