Evaluation of a new 3-dimensional color Doppler flow method to quantify flow across the mitral valve and in the left ventricular outflow tract: an in vitro study

Color Flow Ultrasound Spatial Sampling Beam Density for Partial Volume-Corrected Three-Dimensional Volume Flow (3DVF): Theory, Simulation, and Experiment

OBJECTIVE

The purpose of this study was to quantify the accuracy of partial volume-corrected three-dimensional volume flow (3DVF) measurements as a function of spatial sampling beam density using carefully-designed parametric analyses in order to inform the target applications of 3DVF.

METHODS

Experimental investigations employed a mechanically-swept curvilinear ultrasound array to acquire 3D color flow (6.3 MHz) images in flow phantoms consisting of four lumen diameters (6.35, 4.88, 3.18 and 1.65 mm) with volume flow rates of 440, 260, 110 and 30 mL/min, respectively. Partial volume-corrected three-dimensional volume flow (3DVF) measurements, based on the Gaussian surface integration principle, were computed at five regions of interest positioned between depths of 2 and 6 cm in 1 cm increments. At each depth, the color flow beam point spread function (PSF) was also determined, using in-phase/quadrature data, such that 3DVF bias could then be related to spatial sampling beam density. Corresponding simulations were performed for a laminar parabolic flow profile that was sampled using the experimentally-measured PSFs. Volume flow was computed for all combinations of lumen diameters and the PSFs at each depth.

RESULTS

Accurate 3DVF measurements, i.e., bias less than ±20%, were achieved for spatial sampling beam densities where at least 6 elevational color flow beams could be positioned across the lumen. In these cases, greater than 8 lateral color flow beams were present. PSF measurements showed an average lateral-to-elevational beam width asymmetry of 1:2. Volume flow measurement bias increased as the color flow beam spatial sampling density within the lumen decreased.

CONCLUSION

Applications of 3DVF, particularly those in the clinical domain, should focus on areas where a spatial sampling density of 6 × 6 (lateral x elevational) beams can be realized in order to minimize measurement bias. Matrix-based ultrasound arrays that possess symmetric PSFs may be advantageous to achieve adequate beam densities in smaller vessels.

Three-dimensional US for Quantification of Volumetric Blood Flow: Multisite Multisystem Results from within the Quantitative Imaging Biomarkers Alliance

Background Quantitative blood flow (QBF) measurements that use pulsed-wave US rely on difficult-to-meet conditions. Imaging biomarkers need to be quantitative and user and machine independent. Surrogate markers (eg, resistive index) fail to quantify actual volumetric flow. Standardization is possible, but relies on collaboration between users, manufacturers, and the U.S. Food and Drug Administration. Purpose To evaluate a Quantitative Imaging Biomarkers Alliance-supported, user- and machine-independent US method for quantitatively measuring QBF. Materials and Methods In this prospective study (March 2017 to March 2019), three different clinical US scanners were used to benchmark QBF in a calibrated flow phantom at three different laboratories each. Testing conditions involved changes in flow rate (1-12 mL/sec), imaging depth (2.5-7 cm), color flow gain (0%-100%), and flow past a stenosis. Each condition was performed under constant and pulsatile flow at 60 beats per minute, thus yielding eight distinct testing conditions. QBF was computed from three-dimensional color flow velocity, power, and scan geometry by using Gauss theorem. Statistical analysis was performed between systems and between laboratories. Systems and laboratories were anonymized when reporting results. Results For systems 1, 2, and 3, flow rate for constant and pulsatile flow was measured, respectively, with biases of 3.5% and 24.9%, 3.0% and 2.1%, and -22.1% and -10.9%. Coefficients of variation were 6.9% and 7.7%, 3.3% and 8.2%, and 9.6% and 17.3%, respectively. For changes in imaging depth, biases were 3.7% and 27.2%, -2.0% and -0.9%, and -22.8% and -5.9%, respectively. Respective coefficients of variation were 10.0% and 9.2%, 4.6% and 6.9%, and 10.1% and 11.6%. For changes in color flow gain, biases after filling the lumen with color pixels were 6.3% and 18.5%, 8.5% and 9.0%, and 16.6% and 6.2%, respectively. Respective coefficients of variation were 10.8% and 4.3%, 7.3% and 6.7%, and 6.7% and 5.3%. Poststenotic flow biases were 1.8% and 31.2%, 5.7% and -3.1%, and -18.3% and -18.2%, respectively. Conclusion Interlaboratory bias and variation of US-derived quantitative blood flow indicated its potential to become a clinical biomarker for the blood supply to end organs. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Forsberg in this issue.

Quantification of the area and shunt volume of multiple, circular, and noncircular ventricular septal defects: A 2D/3D echocardiography comparison and real time 3D color Doppler feasibility determination study

BACKGROUND

Quantification of defect size and shunt flow is an important aspect of ventricular septal defect (VSD) evaluation. This study compared three-dimensional echocardiography (3DE) with the current clinical standard two-dimensional echocardiography (2DE) for quantifying defect area and tested the feasibility of real time 3D color Doppler echocardiography (RT3D-CDE) for quantifying shunt volume of irregular shaped and multiple VSDs.

METHODS

Latex balloons were sutured into the ventricles of 32 freshly harvested porcine hearts and were connected with tubing placed in septal perforations. Tubing was varied in area (0.13-5.22 cm²), number (1-3), and shape (circle, oval, crescent, triangle). A pulsatile pump was used to pump "blood" through the VSD (LV to RV) at stroke volumes of 30-70 mL with a stroke rate of 60 bpm. Two-dimensional echocardiography (2DE), 3DE, and RT3D-CDE images were acquired from the right side of the phantom.

RESULTS

For circular VSDs, both 2DE and 3DE area measurements were consistent with the actual areas (R² = 0.98 vs 0.99). For noncircular/multiple VSDs, 3DE correlated with the actual area more closely than 2DE (R² = 0.99 vs 0.44). Shunt volumes obtained using RT3D-CDE positively correlated with pumped stroke volumes (R² = 0.96).

CONCLUSIONS

Three-dimensional echocardiography (3DE) is a feasible method for determining VSD area and is more accurate than 2DE for evaluating the area of multiple or noncircular VSDs. Real-time 3D color Doppler echocardiography (RT3D-CDE) is a feasible method for quantifying the shunt volume of multiple or noncircular VSDs.

Quantification of Shunt Volume Through Ventricular Septal Defect by Real-Time 3-D Color Doppler Echocardiography: An in Vitro Study

Quantification of shunt volume is important for ventricular septal defects (VSDs). The aim of the in vitro study described here was to test the feasibility of using real-time 3-D color Doppler echocardiography (RT3-D-CDE) to quantify shunt volume through a modeled VSD. Eight porcine heart phantoms with VSDs ranging in diameter from 3 to 25 mm were studied. Each phantom was passively driven at five different stroke volumes from 30 to 70 mL and two stroke rates, 60 and 120 strokes/min. RT3-D-CDE full volumes were obtained at color Doppler volume rates of 15, 20 and 27 volumes/s. Shunt flow derived from RT3-D-CDE was linearly correlated with pump-driven stroke volume (R = 0.982). RT3-D-CDE-derived shunt volumes from three color Doppler flow rate settings and two stroke rate acquisitions did not differ (p > 0.05). The use of RT3-D-CDE to determine shunt volume though VSDs is feasible. Different color volume rates/heart rates under clinically/physiologically relevant range have no effect on VSD 3-D shunt volume determination.

Real Time Three-Dimensional Echocardiographic Evaluations of Fetal Left Ventricular Stroke Volume, Mass, and Myocardial Strain: In Vitro and In Vivo Experimental Study

BACKGROUND

Left ventricular stroke volume, mass, and myocardial strain are valuable indicators of fetal heart function. This study investigated the feasibility of nongated real time three-dimensional echocardiography (RT3DE) to determine fetal stroke volume (SV), left ventricular mass (LVM), and myocardial strain under different conditions.

METHODS

To evaluate fetal hearts, fetal-sized rabbit hearts were used in this study. The in vitro portion of this study was carried out using a balloon inserted into the LV of eight fresh rabbit hearts and driven by a calibrated pulsatile pump. RT3DE volumes were obtained at various pump-set SVs. The in vivo experiments in this study were performed on open-chest rabbits. RT3DE volumes were acquired at the following conditions: baseline, simulated hypervolemia, inferior vena cava (IVC) ligation, and ascending aorta (AAO) ligation. Displacement values and sonomicrometry data were used as references for RT3DE-derived SV, LVM, longitudinal strain (LS), and circumferential strain (CS).

RESULTS

Excellent correlations between RT3DE-derived values and reference values were demonstrated and accompanied by high coefficients of determination (R(2) ) for both in vitro and in vivo studies for SV, LVM, LS, and CS (in vitro: SV: R(2)  = 0.98; LVM: R(2)  = 0.97; LS: R(2)  = 0.87, CS: R(2)  = 0.80; in vivo: SV: R(2)  = 0.92; LVM: R(2)  = 0.98; LS: in vivo: R(2)  = 0.84; CS: in vivo: R(2)  = 0.76; all P < 0.05).

CONCLUSIONS

RT3DE is capable of quantifying the SV, LVM, and myocardial strain of fetal-sized hearts under different conditions. This nongated RT3DE may aid the evaluation of fetal cardiac function, providing a superior understanding of the progress of fetal heart disorders.