• There are two approaches that are commonly used for LV quantification from RT3DE datasets (Fig. 1-3): (A) 3D-guided biplane technique—by selecting from a pyramidal dataset two anatomically correct non-foreshortened 2D views, from which LV volumes are calculated using a biplane approximation, and (B) direct volume quantification—based on semi-automated detection of LV endocardial surfaces followed by calculation of the volume contained within this surface.

• When compared with conventional 2D echocardiographic measurements, RT3DE-derived LV volumes and ejection fraction (EF) show higher levels of agreement with the respective reference technique, such as radionuclide ventriculography or cardiac magnetic resonance imaging (MRI).

• RT3DE-derived LV volumes and EF are more reproducible than 2D measurements.

• The improved accuracy and reproducibility of RT3DE-based LV volume and EF measurements is of vital importance because clinical decision making relies heavily on these measurements.

• Despite the improved accuracy and reproducibility, recent studies have reported that RT3DE consistently underestimates LV volumes.

• Tracing errors were identified as the main cause of volume underestimation, since the spatial resolution of RT3DE images may not be sufficiently high to differentiate between the myocardium and endocardial trabeculae in all patients (Fig. 1-4).

Figure 1-3 Two approaches to measure left ventricular (LV) volume from real-time three-dimensional echocardiography (RT3DE) datasets: (A) 3D-guided biplane analysis based on selecting from the entire 3D dataset anatomically correct, nonforeshortened, apical two- and four-chamber views and then using the biplane calculation identical to that used with 2D imaging, and (B) direct phase-by-phase volumetric analysis based on counting pixels contained inside the 3D endocardial surface, which results in a volume over time curve (green curve). Key: √, resolved; ×, remains unresolved.

(Reproduced from Mor-Avi V, Lang RM. The use of real-time three-dimensional echocardiography for the quantification of left ventricular volumes and function. Curr Opin Cardiol. 2009;24:402-409, Figure 2.)

Figure 1-4 RT3DE images obtained in two patients: (A) with optimal endocardial visualization that allows accurate differentiation between the myocardium and the papillary muscle and endocardial trabeculae, and (B) with suboptimal endocardial visualization that is likely to result in inaccurate LV volume measurements.

(Reproduced from Mor-Avi V, Jenkins C, Kühl HP, et al. Real-time 3-dimensional echocardiographic quantification of left ventricular volumes: multicenter study for validation with magnetic resonance imaging and investigation of sources of error. J Am Coll Cardiol Imaging. 2008;1:413-423, Figure 4.)

Technical Considerations

• While the 3D-guided biplane technique (A) can minimize LV foreshortening, it still relies on geometric modeling to calculate volumes, and is thus likely to be inaccurate in distorted ventricles.

• Because direct volumetric quantification (B) is not affected by LV foreshortening and does not rely on geometric modeling, this approach is more accurate even in the presence of wall motion abnormalities and distorted ventricular shape.

• While volumetric quantification requires specialized software, the 3D-guided biplane technique is a reasonably accurate alternative for LV volume measurements.

• Tracing errors can be minimized by learning how to identify the true endocardial boundary beyond the blood-trabeculae interface and trace it as far out as possible, so as to include the papillary muscles and endocardial trabeculae in the LV cavity.

Left Ventricular Mass

• LV mass is an important predictor of morbidity and mortality, especially in patients with systemic hypertension.

• In addition to accurate detection of the endocardial boundaries, LV mass measurements rely on accurate detection of the epicardium (Fig. 1-5, left and middle), which in most patients is extremely challenging.

• LV mass can also be measured using either one of the two approaches utilized to measure LV volumes from RT3DE datasets: the 3D-guided biplane technique or volumetric analysis (see Fig. 1-3).

• RT3DE-derived LV mass measurements avoid the use of foreshortened apical views (see Fig. 1-5, right).

• As a result, RT3DE-derived LV mass measurements are more accurate than the conventional biplane 2D techniques (Fig. 1-6, left).

• Also, RT3DE-derived LV mass measurements are more reproducible (see Fig. 1-6, right), because they are less view dependent.

Figure 1-5 Comparison between 2D biplane (left) and 3D-guided biplane calculation of LV mass (middle). Because in the majority of patients LV apical views are foreshortened by 2D imaging (right), the calculated LV mass is underestimated when compared with magnetic resonance imaging (MRI) reference values. In contrast, RT3DE imaging allows avoiding foreshortened views and results in more accurate measurements.

(Reproduced from Mor-Avi V, Sugeng L, Weinert L, et al. Fast measurement of left ventricular mass with real-time three-dimensional echocardiography: comparison with magnetic resonance imaging. Circulation. 2004;110:1814-1818, Figures 1 and 5.)

Figure 1-6 Side-by-side comparison between 2D biplane and 3D-guided biplane calculation of LV mass to MRI reference values in a group of patients (left), showing that the 2D technique underestimates LV mass, while the 3D technique results in more accurate measurements compared with a reference technique (middle). In addition, the 3D technique showed better reproducibility compared with the 2D methodology (right).

Technical Considerations

• To obtain accurate LV mass measurements from RT3DE datasets, the same guidelines for endocardial tracing as for LV volume measurements (see above) should be strictly followed to avoid underestimation of LV mass.

• In addition, epicardial boundaries should be carefully initialized and adjusted when necessary in multiple views.

• While volumetric quantification requires specialized software, the 3D-guided biplane technique is a reasonably accurate alternative for LV mass measurements.

Left Ventricular Wall Motion

• Echocardiography is the most widely clinically used imaging modality for the evaluation of regional LV function. This is usually achieved by visual inspection of the beating ventricle in multiple cross-sectional planes that depict all 17 myocardial segments.

• The ability to capture the complete dynamic information of the LV in a single heartbeat lends itself to the analysis of regional wall motion.

• RT3DE allows visualization and evaluation of LV wall motion in different planes. Once the 3D dataset is acquired, image planes can be extracted in any desired orientation.

• Importantly, the ability to visualize the same LV segment in multiple planes can help in determining the extent and severity of the wall motion abnormality.

• Beyond visual interpretation, dynamic RT3DE datasets can be analyzed to obtain objective quantitative measurements of regional LV function. One such measure is segmental EF, which can be accurately calculated from segmental volumes (Fig. 1-7).

• A decrease in segmental EF reflects reduced regional wall motion.

• All these features translate into improved accuracy of the echocardiographic diagnosis of ischemic heart disease.

Figure 1-7 Endocardial surface extracted from an RT3DE dataset (A) can be divided into segments corresponding to specific LV walls (B). For each wall, segmental volume can be obtained over time throughout the cardiac cycle (C). From these curves, a variety of quantitative indices of regional LV systolic and diastolic function, including segmental ejection fraction, can be calculated.

Stress Testing

• Although stress echocardiography has become a widely used technique for the diagnosis and risk stratification of patients with suspected or known coronary artery disease, 2D stress echocardiography has methodologic limitations.

• 2D image acquisition during peak exercise may be impaired by: (1) probe positioning errors resulting in inadequate image planes; (2) reduced quality of transthoracic images with poor visualization of LV walls; (3) time-consuming acquisition of multiple imaging planes that need to be acquired within a narrow time window, while wall motion abnormalities are still present; and (4) subjectivity of image interpretation leading to poor interobserver agreement.

• Several of these limitations can be solved using RT3DE, which allows simultaneous visualization and evaluation of LV wall motion in different planes at different levels of the LV. Besides the conventional two-, three- and four-chamber views, multiple parallel short axis slices can be used for systematic assessment of regional wall motion, including side-by-side comparisons of rest and stress (Fig. 1-8).

• While acquisition of a complete pyramidal dataset greatly reduces the time required to capture a complete set of views during a stress test, serial acquisition of subvolumes during consecutive heartbeats is not ideal because of the rapid changes in heart rate.

• The alternative of simultaneous acquisition of multiple planes using either biplanar imaging (two orthogonal or nonorthogonal views) or triplanar imaging (three planes at 60-degree increments) also represents an improvement over 2D imaging (Fig. 1-9).

• Both exercise stress (either bicycle or treadmill) and pharmacological stress (mainly dobutamine plus atropine), which improves image quality and increases the available time for imaging during peak stress, have been used with RT3DE techniques.

• To improve endocardial delineation when necessary, left heart contrast agents have been used with stress RT3DE as well (Fig. 1-10).

• One advantage of contrast-enhanced biplane or triplane imaging for stress testing is that conventional 2D harmonic settings can be used, while acquisition of pyramidal volume datasets with contrast enhancement relies on settings that are not yet well defined and optimized.

• The biggest advantage of the RT3DE stress test with contrast is that the improvement in endocardial visualization is achieved with a single contrast injection.

Figure 1-8 Off-line viewing of RT3DE data obtained during stress test allows extracting multiple short axis views at different levels of the left ventricle (LV) (top) simultaneously acquired at rest (bottom left) or during peak stress (bottom right).

(Reproduced from Lang RM, Mor-Avi V, Sugeng L, et al. Three-dimensional echocardiography: the benefits of the additional dimension. J Am Coll Cardiol. 2006;48:2053-2069, Figure 6.)