Influence of echocardiographic scan plane location and number on the accuracy of three-dimensional left ventricular volume and shape determination

Relation between number of component views and accuracy of left ventricular mass determined by three-dimensional echocardiography

Three-dimensional echocardiography (3DE) allows the accurate determination of left ventricular (LV) mass, but the optimal number of component or extracted 2-dimensional (2D) image planes that should be used to calculate LV mass is not known. This study was performed to determine the relation between the number of 2D image planes used for 3DE and the accuracy of LV mass, using cardiovascular magnetic resonance (CMR) imaging as the reference standard. Three-dimensional echocardiography data sets were analyzed using 4, 6, 8, 10 and 20 component 2D planes as well as biplane 2D echocardiography and CMR in 25 subjects with a variety of LV pathologies. Repeated-measures analysis of variance and the Bland-Altman method were used to compare measures of LV mass. To further assess the potential clinical impact of reducing the number of component image planes used for 3DE, the number of discrepancies between CMR and each of the 3DE estimates of LV mass at prespecified levels (i.e., > or =5%, > or =10%, and > or =20% difference from CMR LV mass) was tabulated. The mean LV mass by magnetic resonance imaging was 177 +/- 56 g (range 91 to 316). Biplane 2-dimensional echocardiography significantly underestimated CMR LV mass (p <0.05), but LV mass by 3DE was not statistically different from that by CMR regardless of the number of planes used. However, error variability and Bland-Altman 95% confidence intervals decreased with the use of additional image planes. In conclusion, transthoracic 3DE measures LV mass more accurately than biplane 2-dimensional echocardiography when > or =6 component 2D image planes are used. The use of >6 planes further increases the accuracy of 3DE, but at the cost of greater analysis time and potentially increased scanning times.

Characterizing the normal heart using quantitative three-dimensional echocardiography

We present normative data on cardiac volume, geometry and shape derived using three-dimensional echocardiography (3-DE). Three-dimensional reconstructions were created using the piecewise smooth surface subdivision (PSSS) reconstruction technique of the left and right ventricular (LV and RV) endocardium and the mitral and tricuspid annuli (MA and TA) of 67 normal subjects. We derived LV end-diastolic (ED) and end-systolic (ES) volume indices (VI) of 76.5 +/- 16.8 ml m(-2) and 35.3 +/- 14.1 ml m(-2), LV ejection fraction (EF) of 56.1 +/- 9.93%, RV EDVI and ESVI of 93.2 +/- 20.0 ml m(-2) and 49.9 +/- 13.5 ml m(-2) and RVEF of 47.3 +/- 7.69%, along with data on the geometry and shape of the MA, TA, LV and RV. There was no pattern of consistent understatement or overstatement of volumes or dimensions compared with other imaging modalities, and observed variance in data can largely be accounted for through examination of the physics or protocol of each modality.

Visual quantitative estimation: semiquantitative wall motion scoring and determination of ejection fraction

Ejection fraction (EF) is the most commonly used parameter of left ventricular (LV) systolic function and can be assessed by echocardiography. Quantitative echocardiography is time consuming and is as accurate as visual estimation, which has significant variability. We hypothesized that each echocardiographer has developed a mental set of guidelines that relate to how much individual segment shortening constitutes normal function or hypokinesis of varying extents. We determined the accuracy of applying these guidelines to an accepted technique of EF determination using a retrospective analysis of consecutive two-dimensional echocardiographic studies performed on patients who had radioventriculography (RVG) within 48 hours. Using a 12 segment model, we scored each segment at the base and mid-ventricular level based on segmental excursion and thickening. The apex was scored similarly but with 1/3 of the value based on a cylinder-cone model. EF was determined from the sum of segment scores and was estimated visually. We termed this approach visual quantitative estimation (VQE). We correlated the EF derived from VQE and visual estimation with RVG EF. In the training set, VQE demonstrated a strong correlation with RVG (r = 0.969), which was significantly greater than visual estimation (r = 0.896, P < 0.01). The limits of agreement for VQE (+12% to -7%) were similar to the limits of RVG agreement with contrast ventriculography (+10% to -11%) with similar intraobserver and interobserver variabilities. Similar correlation was noted in the prediction set between VQE and RVG EF (r = 0.967, P < 0.001). We conclude that VQE provides highly correlated estimates of EF with RVG.

Rapid and accurate left ventricular surface generation from three-dimensional echocardiography by a catalog based method. Rapid LV surface generation by three-dimensional echo

BACKGROUND

Quantitative analysis from three-dimensional (3D) echocardiography requires accurate reconstruction of left ventricular (LV) surfaces. This currently requires time-consuming manual image tracing. We describe and validate an alternative rapid method of generating LV surfaces.

METHODS

A 3D-image set is acquired using transthoracic scanning. Images from five standard echo views are displayed and border points selected where anatomic landmarks are well defined. A LV surface is reconstructed as a convex weighted sum of LVs from a catalog of 80 LVs. The intersections of the surface with the five views are presented on these images. The routine may be rerun until the LV surface matches the images. One LV surface is generated in 3 min +/- 27 s. In 41 studies (19 normal, 15 previous infarction, seven cardiomyopathy) the volumes of the catalog-fit endocardial and epicardial surfaces were compared with volumes from surfaces reconstructed from full manual tracing.

RESULTS

Over a wide range of LV volumes and ejection fraction (EF), the catalog-fit results correlated closely to those from manual tracing: end-diastolic volume (194 +/- 99 vs. 204 +/- 110 ml, y = 0.93x, R2 = 0.99, SEE = 19 ml, p < 0.001), end-systolic volume (122 +/- 95 vs. 131 +/- 106 ml, y = 0.92x, R2 = 0.99, SEE = 13 ml, p < 0.001), EF (42 +/- 16 vs. 42 +/- 15%, y = x, R2 = 0.99, SEE = 4%, p < 0.001) and mass (220 +/- 88 vs. 204 +/- 86 g, y = 1.1x, R2 = 0.99, SEE = 24 g, p < 0.001). The endocardial catalog surface was generated from an average of 20 points and three computational runs for both end-diastole and end-systole.

CONCLUSIONS

The catalog method of LV reconstruction from 3D-echo provides accurate measurement of volume, EF and mass. The speed of the method is a major advantage.

Importance of transducer displacement and tilting on three-dimensional echocardiographic volume assessment using apical or off-axis rotational acquisition: an in vitro study

OBJECTIVE

The goal of this study was to assess effects of translation (horizontal displacement) and angulation (transducer tilting) on 3-dimensional (3D) echocardiographic volumes of both balloons and human left ventricles after autopsy.

METHODS

Six water-filled (non-) aneurysmatic balloons of 150, 250, and 350 mL and 3 hearts of different sizes and shapes were suspended upright in a water bath. Angulation and/or translation was performed respectively by tilting the transducer with a mechanical arm in a vertical plane relative to the balloon tip or true apex of the hearts and by shifting the water bath in the same vertical plane. For balloon and left ventricular (LV) volume assessment, a 3D conical data set was obtained by TomTec rotational acquisition in combination with a HP Sonos 5500 ultrasound machine.

RESULTS

For the 6 balloons, translation from 1 to 4 cm yielded volumes of up to 74% of the optimal volume (100%); angulation of 10 degrees or 20 degrees, volumes of up to 80% and 34%. Translation with 10-degree angulation yielded volumes up to 64%; for 20-degree angulation and translation, there was no volume loss. Results were similar for the left ventricles.

CONCLUSIONS

Even minor angulation or translation of the transducer yields substantial underestimation of the true volume. Off-axis para-apical views, however, defined as angulation of 20 degrees and greater than 0.5 cm translation in this in vitro model, obviate volume underestimation. Such views in patients, if obtainable, may be an attractive alternative for conventional apical 3D acquisition, especially in dilated and aneurysmatic hearts.