Three-dimensional echocardiography: In vitro and in vivo validation of left ventricular mass and comparison with conventional echocardiographic methods

Objectives. This study aimed to validate a method for mass computation in vitro and in vivo and to compare it with conventional methods.Background. Conventional echocardiographic methods of determining left ventricular mass are limited by assumptions of ventricular geometry and image plane positioning. To improve accuracy, we developed a three-dimensional echocardiographic method that uses nonparallel, nonintersecting short-axis planes and a polyhedral surface reconstruction algorithm for mass computation.Methods. Eleven fixed hearts were imaged by three-dimensional echocardiography, and mass was determined in vitro by multiplying the myocardial volume by the density of each heart and comparing it with the true mass. Mass at diastole and systole by three-dimensional echocardiography and magnetic resonance imaging (MRI) was compared in vivo in 15 normal subjects. Ten subjects also underwent imaging by one- and two-dimensional echocardiography, and mass was determined by Penn convention, area-length and truncated ellipsoid algorithms.Results. In vitro results were r = 0.995, SEE 2.91 g, accuracy 3.47%. In vivo interobserver variability for systole and diastole was 16.7% to 27%, 14% to 18.1% and 6.3% to 12.8%, respectively, for one-, two- and three-dimensional echocardiography and was 7.5% for MRI at end-diastole. The latter two agreed closely with regard to diastolic mass (r = 0.895, SEE 11.1 g) and systolic mass (r = 0.926, SEE 9.2 g). These results were significantly better than correlations between MRI and the Penn convention (r = 0.725, SEE 25.6 g for diastole; r = 0.788, SEE 28.7 g for systole), area-length (r = 0.694, SEE 24.2 g for diastole; r = 0.717, SEE 28.2 g for systole) and truncated ellipsoid algorithms (r = 0.687, SEE 21.8 g for diastole; r = 0.710, SEE 24.5 g for systole).Conclusions. Image plane positioning guidance and elimination of geometric assumptions by three-dimensional echocardiography achieve high accuracy for left ventricular mass determination in vitro. It is associated with higher correlations and lower standard errors than conventional methods in vivo.     

Validation of real-time three-dimensional echocardiography for quantifying left ventricular volumes in the presence of a left ventricular aneurysm: in vitro and in vivo studies

OBJECTIVES: To validate the accuracy of real-time three-dimensional echocardiography (RT3DE) for quantifying aneurysmal left ventricular (LV) volumes. BACKGROUND: Conventional two-dimensional echocardiography (2DE) has limitations when applied for quantification of LV volumes in patients with LV aneurysms. METHODS: Seven aneurysmal balloons, 15 sheep (5 with chronic LV aneurysms and 10 without LV aneurysms) during 60 different hemodynamic conditions and 29 patients (13 with chronic LV aneurysms and 16 with normal LV) underwent RT3DE and 2DE. Electromagnetic flow meters and magnetic resonance imaging (MRI) served as reference standards in the animals and in the patients, respectively. Rotated apical six-plane method with multiplanar Simpson's rule and apical biplane Simpson's rule were used to determine LV volumes by RT3DE and 2DE, respectively. RESULTS: Both RT3DE and 2DE correlated well with actual volumes for aneurysmal balloons. However, a significantly smaller mean difference (MD) was found between RT3DE and actual volumes (-7 ml for RT3DE vs. 22 ml for 2DE, p = 0.0002). Excellent correlation and agreement between RT3DE and electromagnetic flow meters for LV stroke volumes for animals with aneurysms were observed, while 2DE showed lesser correlation and agreement (r = 0.97, MD = -1.0 ml vs. r = 0.76, MD = 4.4 ml). In patients with LV aneurysms, better correlation and agreement between RT3DE and MRI for LV volumes were obtained (r = 0.99, MD = -28 ml) than between 2DE and MRI (r = 0.91, MD = -49 ml). CONCLUSIONS: For geometrically asymmetric LVs associated with ventricular aneurysms, RT3DE can accurately quantify LV volumes.     

Echocardiographic determination of left ventricular dimensions, volumes and performance

Left ventricular dimensions determined by echocardiography in 21 patients were compared by linear regression analysis to biplane angiographic measurements. The results showed significant correlations between the end-diastolic diameter, wall thickness and dimensional ejection fraction obtained by ultrasound and by angiography. The left ventricular volumes derived by the area-length method related closely to the echocardiographic volumes at end-diastole and end-systole. Angiographic stroke volumes showed high correlations with the volumetric change during the cardiac cycle. Determinations of left ventricular mass by echocardiography proved to correlate well with those derived from angiocardiograms. However, satisfactory ultrasonic examinations could not be obtained from 6 (22 percent) of the patient group, who had pulmonary emphysema, cardiomegaly or an exceptionally thick anterior chest wall which caused attenuation of the sound energy.     

Count-based scintigraphic method to calculate ventricular volumes in children: in vitro and clinical validation

A "phantom" was used to validate 1) estimates of different depths of a constant radioactivity source, and 2) the calculation of different volumes using a constant depth and different attenuation coefficients. Using data from this in vitro study, scintigraphic estimates of right ventricular volume and ejection fraction were compared with those obtained by cineangiography in 36 children with either a normal right ventricle or various right ventricular diseases. The static program accurately estimates the distance from the radiation source to the collimator surface (r = 0.99). Radionuclide count methods best predict "phantom" volumes using attenuation coefficients between 0.11(-1) and 0.13(-1) cm. A coefficient of 0.10(-1) underestimates, whereas 0.15(-1) cm grossly overestimates actual volumes. In vivo data were therefore analyzed using an attenuation coefficient of 0.11(-1) with right ventricular counts corrected using either right ventricular or left ventricular background. Closest agreement between scintigraphic and cineangiographic volumes was obtained using right ventricular background, although end-diastolic volumes larger than 100 ml were substantially underestimated. On the basis of this study, the use of two different attenuation coefficients is suggested: the smaller 0.11(-1) cm to calculate end-systolic and end-diastolic volumes and the larger 0.15(-1) cm for volumes greater than 100 ml.     

Left ventricular volumes by single-plane cineangiography: in vivo validation of the Kennedy regression equation

This study was performed to assess the accuracy and reliability of the regression equations of Kennedy et al and Wynne et al in the quantitation of single plane left ventricular (LV) volumes. In 15 patients with normal LV function and without intracardiac shunting or valvular insufficiency, gated equilibrium blood pool scintigraphy was performed simultaneously with the measurement of cardiac output (by thermodilution), after which left ventriculography was performed in the 30 degrees right anterior oblique (RAO) projection. From the scintigraphically determined LV ejection fraction (EF) and the thermodilution-measured stroke volume (SV), absolute LV volumes were calculated. The cineangiographic LV volumes obtained with the regression equation of Kennedy et al closely approximated those calculated by scintigraphy/thermodilution, whereas the volumes determined using the regression equation of Wynne et al were larger (p less than 0.05) than the calculated volumes. In 204 patients without intracardiac shunting or valvular insufficiency, SV was measured by the Fick or indicator dilution methods, after which single-plane left ventriculography was performed in the 30 degrees RAO projection. In the 83 patients without coronary artery disease with normal (n = 69) or depressed (n = 14) LVEF, cineangiographic SV (obtained using the regression equation of Kennedy et al) closely approximated forward SV. Similarly, this relation was excellent in the 142 patients whose LVEFs were greater than or equal to 0.50.(ABSTRACT TRUNCATED AT 250 WORDS)     

Right and left ventricular volumes in vitro by a new nongeometric method

We present an evaluation of a new nongeometric technique for calculating right and left ventricular volumes. This method calculates ventricular chamber volumes from multiple cross-sectional echocardiographic views taken from a single point as the echo beam is tilted progressively through the ventricle. Right and left ventricular volumes are calculated from both the approximate short axis and approximate apical position on 20 in vitro human hearts and compared with the actual chamber volumes. The results for both ventricles from both positions are excellent. Correlation coefficients are > 0.95 for all positions; the standard errors are in the range of 5 to 7 mL and the slopes and intercepts for the regression lines are not significantly different from 1 and 0, respectively (except for the left ventricular short-axis intercept). For all positions, approximately 6 to 8 views are needed for peak accuracy (7.5 degrees to 10 degrees separation). This approach offers several advantages. No geometric assumptions about ventricular shape are made. All images are acquired from a single point (or window), and the digitized points can be used to make a three-dimensional reconstruction of the ventricle. Also, during the calculations a volume distribution curve for the ventricle is produced. The shape of this curve can be characteristic for certain situations (ie, right ventricle, short axis) and can be used to make new simple equations for calculating volume. We conclude that this is an accurate nongeometric method for determining both right and left ventricular volumes in vitro.     

Intracardiac echocardiography: computerized detection of left ventricular borders

A semi-automated method for two- and three-dimensional analysis of intracardiac echocardiography (ICE) images and image sequences is reported based on detection of epicardial and endocardial borders using graph searching. The border detection method was applied to 50 ICE images acquired in vivo in five dogs and to 108 images in 16 volumetric ICE image sequences from eight cadaveric pig hearts. The ICE images from the in vivo study showed good correlation between computer-detected and observer-defined left ventricular (LV) cavity areas and epicardial areas (r=0.99, y=0.98x+0.43[cm2]; r=0.99, y=0.98x+1.11[cm2]; respectively). In the cadaveric hearts, the LV volumes were determined with the volume measurement error of 7.6±7.7% and 11.3±11.2% for the aortic valve and mitral valve image sequences, respectively. Our method facilitates an accurate and computationally efficient approach for the quantitative assessment of ICE image data in 2D and 3D.     

Nongeometric determination of left ventricular volumes from equilibrium blood pool scans

This study assesses the utility of a scintigraphic, nongeometric technique for the determination of left ventricular volumes. Accordingly, gated blood pool scintigraphy and cineangiography were performed within a 24 hour period in 22 patients. Scintigraphic volume measurements were calculated from individual frames of a modified 35 ° left anterior oblique projection using an algorithm designed to consider (1) the background-corrected left ventricular activity normalized for activity per milliliter of peripheral venous blood; (2) total study time; (3) number of frames acquired per cardiac cycle; and (4) percent of the cardiac cycle acquired. Angiographic volumes were calculated by the area-length method and the Kennedy regression equation. There was an excellent correlation between scintigraphic and angiographic methods for all volume measurements grouped together (r = 0.985, standard error of the estimate [SEE] = 14.6 ml) as well as for segregated end-diastolic volumes (r = 0.985, SEE = 16.2 ml) and end-systolic volumes (r = 0.988, SEE = 14.7 ml). Prospective testing of the independent ability of scintigraphy to estimate ventricular volumes was provided for by studying an additional 13 patients, and good agreement was found between scintigraphic and angiographic determinations of left ventricular end-systolic and end-diastolic volumes. Thus, radio nuclide techniques, which are independent of geometric assumptions, may be utilized for the quantitation of left ventricular volumes.     

New echocardiographic and angiographic methods for right atrial volume determination: In vitro validation and in vivo results

Until now, right atrial (RA) volume calculation by means of two-dimensional echocardiography (2-DE) has only been attempted in a single plane: the apical four-chamber view. Our study reports a new method for RA volume calculation using two intersecting 2-DE views. For this purpose, silicone rubber casts of 19 human necropsy hearts were obtained and thin-walled natural rubber moulds of the RA casts were prepared. Totally filled with and immersed in water, the moulds could be visualized in the apical four-chamber view and an additional 2-DE plane, the latter corresponding to the subcostal view in vivo. In this view the vertical extension of RA could be estimated. Areas and lengths of RA were determined in the respective planes, and RA volume was calculated by applying the formula, area x length, to two intersecting planes. Finally, volume of the silicone casts was determined angiocardiographically (Angio) using a biplane method (30° RAO, 40° LAO-40° hepatoclavicular). The true RA volume was 106±23 ml (mean±1SD) as determined by water displacement. Using Angio an excellent correlation was found: the calculated volume amounted to 106±23ml; the difference was 5.5±4.8ml (n.s.); Angio vol=0.93 true vol+ 7.77; r=0.95; SEE= 7,4 ml. Volume determination from the apical four-chamber view of 2-DE using a monoplane disk method resulted in a mean volume of 62±17 ml. The mean difference to the true RA volume was 44±16 ml (p < 0.001). When volume calculations were made using the biplane method, a value of 105±22 ml resulted. The mean difference to true volumes was 7.4±4.8 ml: y=0.84x + 15.88; r=0.91; SEE=9.4 ml.In an in vivo study endsystolic RA volumes were calculated in a normal adult population (n=40) from the same intersecting planes as in vitro. A normal value of 38±6 ml/m² was found. In vivo validation using Angio showed a slightly higher normal value of 43=7 ml/m². Thus, 2-DE is highly accurate in determinating RA volume. In the in vitro as well as in the in vivo study the results of monoplane calculations are clearly inferior to a method which also takes account of the vertical extension of RA.     

In vitro and in vivo intravascular ultrasound imaging.

This paper presents our experience with intravascular ultrasound imaging of animal and human arteries in vitro and in vivo using a high-frequency (20 M Hz) ultrasound transducer. In vitro, 32 human coronary artery segments were imaged with intravascular ultrasound and compared with corresponding histological sections. Ultrasound and histology measurements correlated significantly (P less than 0.0001) for coronary artery cross-sectional area (r = 0.94), lumen cross-sectional area (r = 0.85) and wall thickness (r = 0.92). In vivo, 19 sheep and eight human common femoral arteries were imaged and the angiographic lumen diameter of 14 animal and six human arteries was compared to the diameter of the corresponding ultrasound images. Significant correlations were found for lumen diameter in animals and humans (P less than 0.001, r = 0.91 and P less than 0.0001, r = 0.96, respectively). These studies demonstrate that this technique can provide high resolution images of arterial vessels and may have unique advantages in diagnosing atherosclerotic vascular disease and in catheter based therapies.     

Determination of left ventricular mass by real-time three-dimensional echocardiography: in vitro validation

Twenty-one explanted fixed hearts (14 dogs and 7 pigs) were examined to validate newly developed real-time three-dimensional (RT3D) echocardiography for measurement of left ventricular (LV) mass in vitro and to compare its accuracy and variability with those of conventional echocardiographic measurements. There was an excellent correlation and high degree of agreement for the determination of LV mass between RT3D echocardiography and true mass measurement (r = 0.98; standard error of the estimate [SEE] = 7.3 g; absolute difference [AD] = 2.8 g; y = 1.00 x -4.0, interobserver variability; 5.0%). The conventional echocardiographic methods yielded weaker correlations, larger standard errors, and interobserver variability (area-length method: r = 0.90; SEE = 13.3 g; AD = 13.2 g; 13.3 % / truncated ellipsoid method: r = 0.91; SEE = 14.7 g; AD = 10.5 g; 7. 9% / M-mode: r = 0.91; SEE = 16.2 g; AD = 9.4 g; 15.3%). Determination of LV mass by RT3D echocardiography has a high degree of accuracy and is superior to conventional one- and two-dimensional echocardiographic methods.     

In vivo and in vitro evaluation of left ventricular thrombi by two-dimensional echocardiography. Comparison with cineventriculography

The purpose of this study was to assess the capability of two-dimensional echocardiography to identify left ventricular thrombi as compared to standard single plane cineventriculography in 284 patients, who underwent both procedures within 24 hours for diagnostic purposes. In order to obtain informations about the degree of thrombus organization and diagnostic accuracy of the echocardiographic technique, two-dimensional echocardiographic examinations were also performed in 31 thrombi from 16 autopsy specimens. In 249 cases the results were negative and in 14 cases positive by both techniques. Seven cases were positive by cineventriculography but negative by 2D-echocardiography. In seven cases the findings were equivocal by two-dimensional echocardiography; three of them were negative, two positive, and two equivocal by cineventriculography. In two cases the results were negative by two-dimensional echocardiography but equivocal by cineventriculography. Finally five cases were diagnosed to have a thrombus but two-dimensional echocardiography but not by cineventriculography. In two patients, positive by two-dimensional echocardiography, who were on anticoagulant therapy, follow-up studies showed the disappearance of left ventricular thrombi. In all of them the thrombi showed tissue characteristics similar to those of fresh thrombi examined in vitro. Two-dimensional echocardiography seems to be more reliable than cineventriculography for assessing the presence, extension, number, and morphology of left ventricular thrombi. In vitro studies suggest that two-dimensional echocardiography cannot visualize small thrombi, that fibrotic areas may simulate a thrombus and that in some cases under or overestimation is possible.     

Comparative angiographic right and left ventricular volumes

Comparative angiographic right and left ventricular volumes and right and left ventricular ejection fractions have been reported in the same normal infants and children. This relationship was assessed in adult patients to determine if these pediatric observations persist in later life. Seventeen adults, who had both right and left ventricular angiograms and who had no demonstrable organic heart disease, were studied. Right ventricular end-diastolic volume ranged from 54 to 98 (76 +/- 14, mean +/- SD) cc/m2 and left ventricular end-diastolic volume ranged from 48 to 90 (70 +/- 12) cc/m2; p less than 0.03. Right ventricular end-systolic volume ranged from 22 to 47 (33 +/- 8.0) cc/m2 and left ventricular end-systolic volume ranged from 13 to 34 (22 +/- 5.3) cc/m2; p less than 0.00005. Calculated right ventricular stroke volume ranged from 31 to 60 (43 +/- 8.3) cc/m2 and left ventricular stroke volume ranged from 29 to 70 (48 +/- 11) cc/m2; p = NS. Calculated right ventricular ejection fraction ranged from 0.48 to 0.62 (0.57 +/- 0.04) and the left ventricular ejection fraction ranged from 0.57 to 0.84 (0.68 +/- 0.07; p less than 0.00005. Both right ventricular end-systolic and end-diastolic volumes were greater than left ventricular end-systolic and end-diastolic volumes. This resulted in decreased right ventricular ejection fraction compared to left ventricular ejection fraction. The difference between the two ventricles may be due to compliance, muscle mass, and anatomic configuration with a net result of one chamber more completely emptying than the other. Thus it appears that the relationships between right and left ventricular volumes noted in infancy and childhood persist in adult life.     

Endobronchial ultrasound to assess airway wall thickening: validation in vitro and in vivo.

Endobronchial ultrasound (EBUS) allows identification of airway wall structures and could potentially be utilised for in vivo studies of airway thickening in asthma. The present study investigated whether inflation of the fluid-filled balloon sheath over the transducer (necessary to provide sonic coupling with the airway wall) influenced in vitro measurements. In vivo comparability of EBUS with high resolution computed tomography scanning (HRCT), an established method for measuring wall thickness, was determined in control subjects. The airway diameter and wall thickness were studied using EBUS in 24 cartilaginous airways obtained from four sheep, before and after balloon sheath inflation during immersion in saline. To assess EBUS versus HRCT comparability of airway measures in vivo, 12 control subjects underwent imaging of the posterior basal bronchus of the right lower lobe by both techniques. Intra- and interobserver agreement were also assessed. Results with and without the balloon sheath gave comparable measures of airway internal diameter and wall thickness in vitro. Statistical analysis showed agreement between EBUS and HRCT, and intra- and interobserver variability in vivo. The current study concludes that endobronchial ultrasound, which does not present a radiation risk, could be utilised in the in vivo study of cartilaginous airway wall remodelling in respiratory diseases, such as asthma.     

Value and limitations of transesophageal echocardiography in determination of left ventricular volumes and ejection fraction.

Several formulas exist for estimating left ventricular volumes and ejection fraction using conventional two-dimensional echocardiography from transthoracic views. Transesophageal imaging provides superior resolution of endocardial borders but employs slightly different scan planes. The estimation of left ventricular volumes by transesophageal echocardiography has not been validated in human patients. Therefore, the purpose of this study was to compare left ventricular volumes and ejection fraction derived from transesophageal short-axis and four-chamber images with similar variables obtained from ventriculography. End-diastolic and end-systolic volumes and ejection fraction were calculated using modified Simpson's rule, area-length and diameter-length models in 36 patients undergoing left ventriculography. Measurements of left ventricular length were obtained from the transesophageal four-chamber view and areas and diameters were taken from short-axis scans at the mitral valve, papillary muscle and apex levels. Data from transesophageal echocardiographic calculations were compared with end-diastolic volume (mean 172 +/- 90 ml), end-systolic volume (mean 91 +/- 74 ml) and ejection fraction (mean 52 +/- 15%) from cineventriculography using linear regression analysis. The area-length method (r = 0.88) resulted in a slightly better correlation with left ventricular end-diastolic volume than did Simpson's rule (r = 0.85) or area-length (r = 0.84) formulas. For end-systolic volume, the three models yielded similar correlations: Simpson's rule (r = 0.94), area-length (r = 0.93) and diameter-length (r = 0.95). Each of the methods resulted in significant underestimation of diastolic and systolic volumes compared with values assessed with angiography (p less than 0.003). Ejection fraction was best predicted by using the Simpson's rule formula (r = 0.85) in comparison with area-length (r = 0.80) or diameter-length (r = 0.73) formulas. Measurements of left ventricular length by transesophageal echocardiography were smaller for systole (mean 5.7 +/- 1.6 cm) and diastole (mean 7.7 +/- 1.2 cm) than values by ventriculography (mean 9.2 +/- 1.4 and 8.1 +/- 1.6 cm, respectively; p less than 0.0001), suggesting that underestimation of the ventricular length is a major factor contributing to the smaller volumes obtained by transesophageal echocardiography. In conclusion, currently existing formulas can be applied to transesophageal images for predicting left ventricular volumes and ejection fraction. However, volumes obtained by these models are significantly smaller than those obtained with angiography, possibly because of foreshortening in the transesophageal four-chamber view.     

Determination of left ventricular volumes with use of a new nongeometric echocardiographic method: clinical validation and potential application

A new nongeometric echocardiographic technique for measurement of right and left ventricular volumes was recently validated in vitro. With this method, all images are taken from one point on the chest wall as the transducer is tilted through the ventricle. This approach offers several advantages. No geometric assumptions about ventricular shape are made. All images are acquired from the best echocardiographic window. Furthermore, the digitized points can be used to make a three-dimensional reconstruction of the ventricle. The present study addresses the clinical feasibility of imaging the heart from a single pivoting point in short axis and compares the accuracy of the method in determining left ventricular volumes with that of biplane cineangiography. Twenty-four patients underwent echocardiographic studies within 2 h before angiography. At catheterization, volumes determined by the biplane area-length method ranged between 95 and 368 ml at end-diastole and between 15 and 303 ml at end-systole. A good correlation was observed between ventricular volumes by angiography and echocardiography at end-diastole and end-systole (r = 0.92 and 0.96, respectively). Correlations between volumes by the two techniques were equally good in patients with wall motion abnormalities (n = 13; r = 0.97). Ventricular ejection fraction ranged between 18% and 84% at angiography and correlated well with echocardiographic measurements (r = 0.82). Thus, the echocardiographic tilt method provides accurate determination of left ventricular volume and ejection fraction. This nongeometric method offers the potential for the determination of right ventricular volume and three-dimensional display of the heart.