Paraplane analysis from precordial three-dimensional echocardiographic data sets for rapid and accurate quantification of left ventricular volume and function: a comparison with magnetic resonance imaging

Functional assessment of donor and recipient left atrium in heart transplant patients using full-volume three-dimensional echocardiography

BACKGROUND

Atrial function plays an important role in many cardiac conditions, how recipient and donor compartments of left atrium (LA) of transplanted hearts differentially contribute to overall LA function in transplanted hearts has not been described. We tested whether three-dimensional transthoracic echocardiography (3DE) could be used to calculate these compartment-specific atrial functions.

METHODS AND RESULTS

We analyzed 3DE images of 22 consecutive transplant patients who had diagnostic imaging quality (ages 59 ± 16 years) using TomTec Research Arena. The contour of the recipient and total LA were traced frame by frame, and the donor LA volume was calculated as the difference of the total LA volume minus the recipient LA volume. The LA ejection fractions of total LA, donor LA, and recipient LA were also calculated as (LA atrial end-diastolic volume - LA atrial end-systolic volume)/LA atrial end-diastolic volume of each compartment. Interobserver variability of LA volumes for the total, recipient, and donor compartments were 5.6 ± 2.4, 5.4 ± 2.0, and 9.3 ± 3.2 mL, respectively (n = 11). The donor LA ejection fraction was higher than that of recipient (41 ± 18% vs. 30 ± 14%, P = 0.013). When the patients were categorized as asymptomatic (New York Heart Association functional class [NYHA] functional class I) and symptomatic (NYHA functional class II-III), indexed donor LA atrial end-diastolic volume was significantly lower in asymptomatic patients as compared with symptomatic patients.

CONCLUSIONS

Compartment-specific LA volumes can be calculated in orthotopic heart transplant patients using full-volume 3DE. Our findings may suggest that unique contribution of each LA compartment of transplanted hearts toward the symptoms of these patients.

Gated 99mTc-MIBI single-photon emission computed tomography for the evaluation of left ventricular ejection fraction: comparison with three-dimensional echocardiography

OBJECTIVE

Parameters of left ventricular systolic function directly influence the management of patients with suspected coronary artery disease (CAD). Quantitative gated single-photon emission computed tomography (QGS; Cedars-Sinai Medical Center, Los Angeles, CA, USA) allows the computation of left ventricular ejection fraction (LVEF) from myocardial perfusion imaging studies which are frequently performed on patients with suspected CAD. Three-dimensional (3D) echocardiography is considered to be the echocardiographic "gold standard" for the quantification of LVEF. We sought to compare QGS with 3D echocardiography in the evaluation of EF in patients with suspected CAD.

METHODS

Ninety-one consecutive patients with suspected CAD, scheduled for coronary angiography, underwent rest electrocardiographic-gated technetium-99m methoxyisobutylisonitrile SPECT (G-SPECT) with measurement of LVEF by QGS and transthoracic 3D echocardiography with off-line measurement of LVEF (Tomtec 4D LV Analysis 1.1). The diagnosis of CAD was based on coronary angiography, performed on every patient.

RESULTS

Nine patients were excluded from the analysis owing to unsuitability for 3D echocardiography (8 patients) or G-SPECT (1 patient). In the remaining group of 82 patients, 71 (87%) had significant CAD, 34 (42%) had a history of myocardial infarction, and 50 (61%) had perfusion defects at rest G-SPECT images. The mean LVEF measured by QGS and 3D echocardiography was 53+/-13% and 53+/-10%, respectively. The mean difference in LVEF between 3D echocardiography and QGS was 0.1+/-6.0% (P=0.87), and the correlation between the values obtained by both methods was high (r=0.88, P<0.001). The largest discrepancies were observed in patients with small ventricular volumes.

CONCLUSIONS

In patients undergoing diagnostic work-up for CAD, the measurement of LVEF by QGS algorithm provides high correlation and satisfactory agreement with the results of reference ultrasound method--3D echocardiography.

Contrast-enhanced versus non-enhanced three-dimensional echocardiography of left ventricular volumes

BACKGROUND

In three-dimensional echocardiography (3DE), individual endocardial trabeculae are not clearly visible necessitating left ventricular (LV) volumes to be measured by tracing the innermost endocardial contour. Ultrasound contrast agents aim to improve endocardial definition, but may delineate the outermost endocardial contour by filling up intertrabecular space. Although measurement reproducibility may benefit, there may be a significant influence on absolute LV volume measurements.

METHODS

Twenty patients with a recent myocardial infarction and good ultrasound image quality underwent 3DE using the TomTec Freehand method before and during continuous intravenous contrast infusion. LV volumes were measured offline using TomTec Echo-Scan software.

RESULTS

The use of contrast enhancement increased end-diastolic (110+/-35 vs. 144+/-53 ml; p<0.01) and end-systolic volume measurements (68+/-31 vs. 87+/-45 ml; p<0.01) significantly compared with non-contrast; the ejection fraction remained unchanged (40+/-13 vs. 41+/-14%, p=NS). Measurement reproducibility did not improve significantly, however.

CONCLUSION

Volumes measured by 3DE are significantly larger when ultrasound contrast is used. Possibly, intertrabecular space comprises a substantial part of the LV cavity. In the presence of an adequate apical acoustic window, ultrasound contrast does not improve LV volume measurement reproducibility. (Neth Heart J 2008;16:47-52.).

Rapid and Accurate Measurement of Left Ventricular Function with a New Second-Harmonic Fast-Rotating Transducer and Semi-Automated Border Detection

Measurement of left ventricular (LV) volume and function are the most common clinical referral questions to the echocardiography laboratory. A fast, practical, and accurate method would offer important advantages to obtain this important information. To validate a new practical method for rapid measurement of LV volume and function. We developed a continuous fast-rotating transducer, with second-harmonic capabilities, for three-dimensional echocardiography (3DE). Fifteen cardiac patients underwent both 3DE and magnetic resonance imaging (reference method) on the same day. 3DE image acquisition was performed during a 10-second breath-hold with a frame rate of 100 frames/sec and a rotational speed of 6 rotations/sec. The individual images were postprocessed with Matlab software using multibeat data fusion. Subsequently, with these images, 12 datasets per cardiac cycle were reconstructed, each comprising seven equidistant cross-sectional images for analysis in the new TomTec 4DLV analysis software, which uses a semi-automated border detection (ABD) algorithm. The ABD requires an average analysis time of 15 minutes per patient. A strong correlation was found between LV end-diastolic volume (r = 0.99; y = 0.95x - 1.14 ml; SEE = 6.5 ml), LV end-systolic volume (r = 0.96; y = 0.89x + 7.91 ml; SEE = 7.0 ml), and LV ejection fraction (r = 0.93; y = 0.69x + 13.36; SEE = 2.4%). Inter- and intraobserver agreement for all measurements was good. The fast-rotating transducer with new ABD software is a dedicated tool for rapid and accurate analysis of LV volume and function.

Time course of left ventricular volumes in severe congestive heart failure patients treated by optimized AV sequential left ventricular pacing alone--a 3-dimensional echocardiographic study

BACKGROUND

This study evaluates the acute and chronic resynchronizing effects of AV sequential left ventricular (LV) pacing on LV function in patients with impaired cardiac function and conduction disorders by 3-dimensional transesophageal echocardiography.

METHODS AND RESULTS

Twenty-nine patients with congestive heart failure, with LV ejection fraction (LVEF) < or = 30%, QRS duration > or = 120 milliseconds, and New York Heart Association Class II to IV, were implanted with a cardiac resynchronization device using an LV lead only, according to the invasively determined hemodynamic optimal pacing site and AV delay. Patients underwent 3-dimensional transesophageal echocardiography before randomization to treatment (baseline) and at 12-month follow-up (resynchronization--12 months). Three-dimensional volumes were acquired on resynchronization and during intermittent switch-off at intrinsic depolarization. The values of stroke volume were 43.2 +/- 13.3 (intrinsic-baseline), 51.7 +/- 17.4 (intrinsic--12 months), 57.2 +/- 15.6 (resynchronization-baseline), and 64.6 +/- 18.9 (resynchronization--12 months). Analysis of variance demonstrated a significant effect of resynchronization at different periods (P < .001) and a significant time effect (P < .05) for stroke volume. Similar results were observed with ejection fraction (LVEF). No effect was observed with LV end-diastolic volume, whereas a therapy effect with no time effect was observed with LV end-systolic volume.

CONCLUSIONS

A significant acute increase of LV stroke volume and LVEF was found by resynchronization by LV pacing alone. A continuous improvement of LV stroke volume and LVEF occurred with time of follow-up (reverse remodeling). The initial therapeutic effect persisted during 12-month follow-up independently of time of follow-up and QRS width. No significant decrease of LV end-diastolic size during chronic resynchronization was detected in contrast to previous studies with resynchronization by biventricular pacing.

Ventricular Volume and Length in Hypertensive Diastolic Heart Failure

BACKGROUND

Patients with diastolic heart failure are thought to have a normal or small ventricle with impaired ventricular filling that requires increased filling pressure to maintain normal stroke volume. In this study we test the hypothesis that patients with hypertensive diastolic heart failure have increased left ventricular volumes compared with age-, sex-, and body size-matched control subjects.

METHOD

Left ventricular chordal dimensions from 2-dimensional echocardiography and volumes from 3-dimensional echocardiography were obtained in control subjects (n = 96) and patients with hypertensive diastolic heart failure (n = 28) and compared before and after controlling for age, sex, and body size.

RESULTS

Volumes by 3-dimensional echocardiography were significantly larger in the heart failure group than in the control group (P < .05). After matching for age, sex, and body size, volumes remained significantly larger in the patients with heart failure (P < .05). Chordal dimensions were not significantly different between the two groups. Stroke volume and centerline length of the ventricle were significantly increased in the heart failure group compared with matched control subjects (P < .05).

CONCLUSIONS

Our group of patients with hypertensive diastolic heart failure had significantly increased left ventricular volumes and stroke volume compared with control subjects, compatible with volume overload heart failure. Two-dimensional echocardiographic measurement of the ventricular chordal dimension failed to detect this enlargement. Ventricular length appeared to be preferentially increased in the patients with hypertensive diastolic heart failure.

Left ventricular volume estimation in cardiac three-dimensional ultrasound: a semiautomatic border detection approach

RATIONALE AND OBJECTIVES

We propose a semiautomatic endocardial border detection method for three-dimensional (3D) time series of cardiac ultrasound (US) data based on pattern matching and dynamic programming, operating on two-dimensional (2D) slices of the 3D plus time data, for the estimation of full cycle left ventricular volume, with minimal user interaction.

MATERIALS AND METHODS

The presented method is generally applicable to 3D US data and evaluated on data acquired with the Fast Rotating Ultrasound (FRU-) Transducer, developed by Erasmus Medical Center (Rotterdam, the Netherlands), a conventional phased-array transducer, rotating at very high speed around its image axis. The detection is based on endocardial edge pattern matching using dynamic programming, which is constrained by a 3D plus time shape model. It is applied to an automatically selected subset of 2D images of the original data set, for typically 10 equidistant rotation angles and 16 cardiac phases (160 images). Initialization requires the drawing of four contours per patient manually. We evaluated this method on 14 patients against MRI end-diastole and end-systole volumes. Initialization requires the drawing of four contours per patient manually. We evaluated this method on 14 patients against MRI end-diastolic (ED) and end-systolic (ES) volumes.

RESULTS

The semiautomatic border detection approach shows good correlations with MRI ED/ES volumes (r = 0.938) and low interobserver variability (y = 1.005x - 16.7, r = 0.943) over full-cycle volume estimations. It shows a high consistency in tracking the user-defined initial borders over space and time.

CONCLUSIONS

We show that the ease of the acquisition using the FRU-transducer and the semiautomatic endocardial border detection method together can provide a way to quickly estimate the left ventricular volume over the full cardiac cycle using little user interaction.

[Improved analysis of left ventricular function using three-dimensional echocardiography]

Left ventricular geometry and function are important pathophysiologic and prognostic parameters. However, especially in patients with cardiac pathologies left ventricular geometry can be complex. Quantification of left ventricular volumes using conventional two-dimensional echocardiography is only possible when simplifying assumptions of left ventricular geometry are made. In contrast three-dimensional echocardiography allows direct quantification of left ventricular volumes even in complex distortions of left ventricular shape. The availability of real-time three-dimensional echocardiography has brought this technique into clinical practice. Three-dimensional echocardiography is a technique that may be used as a routine echocardiographic method in the near future.

Recent advances in echocardiography

Important recent developments have occurred in echocardiography that are already being used clinically. Portable ultrasound devices that weigh less than five pounds are capable of performing a complete bedside echo exam. An intracardiac echocardiographic catheter has recently been introduced that can be placed intracardiac via a vein and navigated within right heart chambers to obtain detailed anatomical landmarks that guide catheter based interventional procedures such as intracardiac ablation and closure of atrial septal defects and patent foramen ovale. Tissue Doppler imaging is finding its role in detecting mechanical asynchrony in patients with congestive heart failure who might benefit from biventricular pacing. The availability of real-time 3D echocardiography has for the first time made assessment of complex cardiac anatomy possible. This review discusses each of these new developments and their potential impact on the practice of echocardiography and cardiology in general.

A visual approach for the accurate determination of echocardiographic left ventricular ejection fraction by medical students

BACKGROUND

Previously published reports show that there is significant intraobserver, interobserver, and interinstitutional variability in the determination of left ventricular (LV) ejection fraction (EF) by echocardiography. With the increased deployment of echocardiography (eg, handheld devices), there exists a need for developing a simple, intuitive approach for evaluating LVEF that allows a wider range of physicians to accurately and rapidly determine LVEF.

OBJECTIVE

We sought to create a system for assessing LVEF that relies on recognition and matching of patterns, rather than on mathematic calculations and geometric assumptions.

METHODS

A library of videoclips of cardiac function was compiled from 54 patients who spanned the spectrum of LVEF. LVEFs were calculated for these patients using standard echocardiographic methods, with further validation of a subsample using cardiac magnetic resonance imaging measurement of LVEF. The library of images was used to create a software tool for assessing LVEF on the basis of a "template-matching" approach. The software tool was then tested on medical students (N=13) to determine whether it enabled relatively untrained individuals to make accurate LVEF estimates.

RESULTS

Using a template-matching approach for interpretation of echocardiograms, medical students were able to accurately estimate LVEF after only a limited introduction to echocardiography. Their LVEF estimates showed good correlation and agreement with gold standard (r = 0.88, standard square of the estimate = 6.0, limits of agreement = +12.0%, -15.6%).

CONCLUSIONS

A new visual approach for assessing cardiac function using template matching can accurately estimate LVEF. With minimal training, medical students can make LVEF estimates that correlate well with gold standard. The application of this new approach includes allowing for the interpretation of LVEF from echocardiograms to be performed by a broader spectrum of physicians.

Three-dimensional echocardiographic determination of cardiac output at rest and under dobutamine stress: comparison with thermodilution measurements in the ischemic pig model

Determination of cardiac output is a potentially important clinical application of three-dimensional (3-D) echocardiography since it could replace invasive measurements with the Swan-Ganz-catheter. To date, there are no studies available to determine whether cardiac output measured by thermodilution can be predicted reliably under changing hemodynamic conditions. Fifteen pigs with ischemic myocardium were examined under four hemodynamic conditions at rest and under pharmacological stress with 5, 10, and 20 microg/kg/min dobutamine. The 3-D datasets were recorded by means of transesophageal echocardiography. The endocardial definition was enhanced by administering the contrast agent FS069 (Optison). Cardiac output was calculated as the product of stroke volume (end-diastolic - end-systolic volume) and heart rate. The invasive measurements were performed with a continuous thermodilution system. In general, there was moderate correlation between 3-D echocardiography and thermodilution(r = 0.72, P < 0.001). At rest, the 3-D echocardiographic measurements were slightly but significantly lower than the invasive measurements (mean difference 0.6 +/- 0.5L/min,P < 0.001). Under stress with 5, 10, and 20 microg/kg/min dobutamine, there was a marked increase in the deviation (1.3 +/- 0.5L/min,P < 0.001; 1.6 +/- 0.7 L/min,P < 0.001; and 2.1 +/- 1.1L/min,P < 0.001, respectively). The deviation was based on two factors: (1). Under stress, the decreasing number of frames per cardiac cycle acquired with 3-D echocardiography led to imprecise recording of end-diastolic and end-systolic volumes, and thus to an underestimation of cardiac output. At least 30 frames per cardiac cycle are needed to eliminate this effect. (2). There is a systematic difference between 3-D echocardiographic and invasive measurements, which is independent of the imaging rate. This is based on an overestimation of the true values by thermodilution. In conclusion, cardiac output can be determined correctly by 3-D echocardiography for normal heart rates at rest. At elevated heart rates, the temporal resolution of 3-D systems currently available is not adequate for reliable determination. In performing and evaluating future clinical comparative studies, the systematic difference between 3-D echocardiography and thermodilution, based on overestimation by thermodilution, must be taken into account.

Noncompressibility of myocardium during systole with freehand three-dimensional echocardiography

BACKGROUND

Measures of ventricular performance, such as the ejection fraction, assume that myocardium is noncompressible and does not change volume significantly from end diastole to end systole. Although this principle is widely accepted as true, little data exist in the literature to support it. Freehand 3-dimensional (3D) echocardiography has previously been shown to be highly accurate for measurement of myocardial mass and volume. Therefore, we hypothesized that it has sufficient accuracy to test the validity of this assumption. We measured myocardial volume at end diastole and end systole in 2 groups of subjects with hypertrophy.

METHODS

Forty-one healthy young adult athletes and 17 adult patients with hypertension, hypertrophy, normal ejection fraction, and heart failure symptoms underwent examination with freehand 3D echocardiography. Endocardial and epicardial surfaces at end diastole and end systole were reconstructed, and their volumes were computed. From these surface volumes, myocardial volume at end diastole and end systole and epicardial stroke volume and endocardial stroke volume were calculated. These volumes were compared with the 2 sample paired t test.

RESULTS

Myocardial volume was constant from diastole to systole (174.7 +/- 45.3 mL versus 174.6 +/- 45.8 mL; P = not significant), and endocardial and epicardial stroke volumes were identical (76.0 +/- 17.4 mL versus 76.0 +/- 17.1 mL; P = not significant). The average absolute difference between the end-diastolic and end-systolic myocardial volumes was 1.9 mL, or less than 1.1% of end-diastolic volume.

CONCLUSION

Myocardial volume measured with freehand 3D echocardiography does not change significantly during systole. Myocardial volume may be considered noncompressible for purposes of measurement of ventricular function with freehand 3D echocardiography. Comparison of end-diastolic and end-systolic myocardial volumes may be used for quality assurance in performing 3D reconstructions.

Myocardial contraction fraction: a volumetric index of myocardial shortening by freehand three-dimensional echocardiography

OBJECTIVES

This study sought to evaluate myocardial contraction fraction (MCF) as an index of myocardial shortening by comparison to conventional shortening indices in patients with hypertensive hypertrophy, athletes with physiologic hypertrophy and sedentary normal adult subjects.

BACKGROUND

A significant percentage of patients with hypertensive hypertrophy have "normal" or "preserved" left ventricular (LV) systolic function by conventional echocardiographic measures whereas their systolic function is depressed when measured by the two-dimensional echocardiographic mid-wall shortening fraction (MWSF). A three-dimensional echocardiographic measure of myocardial shortening analogous to MWSF has been lacking. We describe a volumetric measure of myocardial shortening, the MCF, as the ratio of stroke volume (SV) to myocardial volume (MV), and hypothesize that it may be useful to compare myocardial performance in patients with different degrees and types of hypertrophy.

METHODS

We compared the MCF using freehand three-dimensional echocardiographic reconstruction of the LV to conventional measures of LV function (ejection fraction [EF], endocardial shortening fraction [SF] and MWSF) in subjects with pathologic hypertensive hypertrophy, heart failure symptoms and preserved EF (n = 17), athletes with physiologic hypertrophy (n = 41) and normal sedentary adults (n = 80).

RESULTS

The EF was in the normal range for all three groups. The MCF was lower in hypertensive hypertrophy compared with normal subjects (0.33 +/- 0.05 vs. 0.44 +/- 0.07, p < 0.01). It also successfully differentiated physiologic hypertrophy from normal subjects (0.50 +/- 0.05 vs. 0.44 +/- 0.07, p < 0.01). The endocardial SF did not distinguish athletes from normal subjects and the MWSF did not distinguish hypertensive from physiologic hypertrophy.

CONCLUSIONS

The MCF, a volumetric measure of myocardial shortening, demonstrates that myocardial shortening is decreased in hypertensive hypertrophy and increased in physiologic hypertrophy. The MCF may be useful in assessing differences in myocardial performance in patients with similar degrees of hypertrophy.

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.

Quantification of aortic regurgitation by real-time 3-dimensional echocardiography in a chronic animal model: computation of aortic regurgitant volume as the difference between left and right ventricular stroke volumes

BACKGROUND

The accuracy of conventional 2-dimensional echocardiographic and Doppler techniques for the quantification of valvular regurgitation remains controversial. In this study, we examined the ability of real-time 3-dimensional (RT3D) echocardiography to quantify aortic regurgitation by computing aortic regurgitant volume as the difference between 3D echocardiographic-determined left and right ventricular stroke volumes in a chronic animal model.

METHODS

Three to 6 months before the study, 6 sheep underwent surgical incision of one aortic valve cusp to create aortic regurgitation. During the subsequent open chest study session, a total of 25 different steady-state hemodynamic conditions were examined. Electromagnetic (EM) flow probes were placed around the main pulmonary artery and ascending aorta and balanced against each other to provide reference right and left ventricular stroke volume (RVSV and LVSV) data. RT3D imaging was performed by epicardial placement of a matrix array transducer on the volumetric ultrasound system, originally developed at the Duke University Center for Emerging Cardiovascular Technology. During each hemodynamic steady state, the left and right ventricles were scanned in rapid succession and digitized image loops stored for subsequent measurement of end-diastolic and end-systolic volumes. Left and right ventricular stroke volumes and aortic regurgitant volumes were then calculated and compared with reference EM-derived values.

RESULTS

There was good correlation between RT3D left and right ventricular stroke volumes and reference data (r = 0.83, y = 0.94x + 2.6, SEE = 9.86 mL and r = 0.63, y = 0.8x - 1.0, SEE = 5.37 mL, respectively). The resulting correlation between 3D- and EM-derived aortic regurgitant volumes was at an intermediate level between that for LVSV and that for RVSV (r = 0.80, y = 0.88x + 7.9, SEE = 10.48 mL). RT3D tended to underestimate RVSV (mean difference -4.7 +/- 5.4 mL per beat, compared with -0.03 +/- 9.7 mL per beat for the left ventricle). There was therefore a small overestimation of aortic regurgitant volume (4.7 +/- 10.4 mL per beat).

CONCLUSION

Quantification of aortic regurgitation through the computation of ventricular stroke volumes by RT3D is feasible and shows good correlation with reference flow data. This method should also be applicable to the quantification of other valvular lesions or single site intracardiac shunts where a difference between right and left ventricular cavity stroke volumes is produced.

Comparison of magnetic resonance real-time imaging of left ventricular function with conventional magnetic resonance imaging and echocardiography

This study analyzes the accuracy of a new real-time magnetic resonance imaging (MRI) technique (acquisition duration, 62 ms/image) and echocardiography for the determination of left ventricular (LV) end-diastolic volume, end-systolic volume, ejection fraction, and muscle mass when compared with turbo gradient echo imaging as the reference standard. Thirty-four patients were examined with digital echocardiography, standard, and real-time MRI. A close correlation was found between the results of real-time imaging and the reference standard for end-diastolic volume, end-systolic volume, and ejection fraction (r >0.95), with a lower correlation for LV muscle mass (r = 0.81). Correlations between echocardiography and the reference standard were lower for all parameters. Real-time MRI enables the acquisition of high-quality cine loops of the entire heart in minimal time without electrocardiographic triggering or breath holding. Thus, patient setup and scan time can be reduced considerably. Results are similar to the reference standard and superior to echocardiography for determining LV volumes and ejection fraction. This technique is a valid alternative to current approaches and can form the basis of every cardiac MRI examination.

Three-dimensional echocardiography paves the way toward virtual reality

The heart is a three-dimensional (3-D) object and, with the help of 3-D echocardiography (3-DE), it can be shown in a realistic fashion. This capability decreases variability in the interpretation of complex pathology among investigators. Therefore, it is likely that the method will become the standard echocardiography examination in the future. The availability of volumetric data sets allows retrieval of an infinite number of cardiac cross-sections. This results in more accurate and reproducible measurements of valve areas, cardiac mass and cavity volumes by obviating geometric assumptions. Typical 3-DE parameters, such as ejection fraction, flow jets, myocardial perfusion and LV wall curvature, may become important diagnostic parameters based on 3-DE. However, the freedom of an infinite number of cross-sections of the heart can result in an often-encountered problem of being "lost in space" when an observer works on a 3-DE image data set. Virtual reality computing techniques in the form of a virtual heart model can be useful by providing spatial "cardiac" information. With the recent introduction of relatively low cost portable echo devices, it is envisaged that use of diagnostic ultrasound (US) will be further boosted. This, in turn, will require further teaching facilities. Coupling of a cardiac model with true 3-D echo data in a virtual reality setting may be the answer.

The role of cardiovascular magnetic resonance in heart failure

Cardiovascular Magnetic Resonance (CMR) is an accepted gold standard for non-invasive, accurate, and reproducible assessment of cardiac mass and function. The interest in its use for viability, myocardial perfusion and coronary artery imaging is also widespread and growing rapidly as the hardware and expertise becomes available in more centres, and the scans themselves become more cost effective. In patients with heart failure, accurate and reproducible serial assessment of remodelling is of prognostic importance and the lack of exposure to ionizing radiation is helpful. The concept of an integrated approach to heart failure and its complications using CMR is fast becoming a reality, and this will be tested widely in the coming few years, with the new generation of dedicated CMR scanners.

A fast rotating scanning unit for real-time three-dimensional echo data acquisition

Most three-dimensional (3-D) echocardiography (3-DE) systems today are based on off-line methods where a large number of cross-sectional 2-D scans have to be acquired sequentially before a 3-D image can be reconstructed. Because acquisition is done step-by-step based on ECG triggering plus respiratory gating, this introduces motion artefacts and takes significant acquisition time. Another 3-D approach is based on 2-D transducers and parallel beam-forming. Such a system is very complex. In this manuscript, a fast continuously-rotating scanning unit, based on a 64-element phased-array transducer, is described. Typical rotation speed of the 3-D unit is 8 rotations per s. Therefore, 16 3-D volume datasets can be acquired per s in real-time. The first clinical examples as acquired with this probe are presented.

Volumetric analysis of the right ventricle in children with congenital heart defects: comparison of biplane angiography and transthoracic 3-dimensional echocardiography

BACKGROUND

Three-dimensional echocardiography is a non-invasive imaging technique. The fact that it permits volumetric analyses independently of geometrical assumptions makes it a putatively useful method for the precise measurement of the volumes of the irregularly shaped right ventricles in children. The aim of this study was to assess the feasibility of this method and its agreement with angiocardiography based estimates of right ventricular volume in children with congenital heart disease.

METHODS

We studied 102 children with congenital heart disease. The angiocardiographic right ventricular volumetry was performed using a biplanar technique using Simpson's rule and corrected with Lange's correction factors. The echo data sets were registered trans-thoracically with a rotating transmitter. Volumes were calculated after manual planimetry by adding the volumes of the individual slices.

RESULTS

Calculation of right ventricular volume echocardiographically was possible only in 34% of patients, mostly infants and toddlers. In comparison to angiocardiography, the measured volumes were 1.1 +/- 6.9 ml (19.5 +/- 34.1%) or 6.3 +/- 9.4 ml (42.5 +/- 33.6%) smaller during systole or diastole, respectively. The limits of agreement were -12.5 and 13.6 ml, or 12.45 and 25.15 ml during systole or diastole, respectively. When plotted to a logarithmical scale, the correlation coefficients r2 were 0.70 for systolic and 0.79 for diastolic measurements.

CONCLUSION

Transthoracic 3-dimensional echocardiography with a rotating transmitter is feasible for volumetry only in small children. The volumes measured were significantly smaller than the ones calculated from the angiocardiographic images. The correlation between the two methods is moderate.

Left atrial volumes assessed by three- and two-dimensional echocardiography compared to MRI estimates

OBJECTIVES

The aim of the present study was to establish the accuracy and reproducibility of left atrial volume measurements by three-dimensional (3D) echocardiography compared to 2D biplane and monoplane measurements.

BACKGROUND

No echocardiographic technique is generally accepted as optimal for estimation of left atrial size.

METHODS

Left atrial volumes of 18 unselected cardiac patients were obtained with magnetic resonance imaging (MRI) (volumes 145 +/- 58 ml). These volumes were compared with those obtained with different echocardiographic methods: a multiplane 3D method based on 90 images acquired by apical probe rotation, a simplified 3D method using only the three standard apical views, and 2D biplane and monoplane methods based on area-length, disc summation and spherical formulas.

RESULTS

The echocardiographic methods significantly underestimated maximum left atrial volumes as obtained by MRI by 14-37% (p < 0.001). Accuracy, expressed as 1 SD of individual estimates around this systematic underestimation, was 25 to 27% for all methods, except for the 2D 2-chamber monoplane method (37%). Interobserver coefficient of variation was between 14 and 20% for all methods (n.s.).

CONCLUSION

All echocardiographic methods significantly underestimated left atrial volumes as obtained by MRI. A minor non-significant improvement in individual echocardiographic estimates by the 3D methods was obtained at the cost of more time consumption. In unselected patients ultrasound image quality precludes significant improvement of left atrial volume measurements by the applied 3D methods.

Artificial neural networks and spatial temporal contour linking for automated endocardial contour detection on echocardiograms: a novel approach to determine left ventricular contractile function

This study investigated the use of artificial neural networks (ANN) for image segmentation and spatial temporal contour linking for the detection of endocardial contours on echocardiographic images. Using a backpropagation network, the system was trained with 279 sample regions obtained from eight training images to segment images into either tissue or blood pool region. The ANN system was then applied to parasternal short axis images of 38 patients. Spatial temporal contour linking was performed on the segmented images to extract endocardial boarders. Left ventricular areas (end-systolic and end-diastolic) determined with the automated system were calculated and compared to results obtained by manual contour tracing performed by two independent investigators. In addition, ejection fractions (EF) were derived using the area-length method and compared with radionuclide ventriculography. Image quality was classified as good in 12 (32%), moderate in 13 (34%) and poor in 13 (34%) patients. The ANN system provided estimates of end-diastolic and end-systolic areas in 36 (89%) of echocardiograms, which correlated well with those obtained by manual tracing (R = 0.99, SEE = 1.44). A good agreement was also found for the comparison of EF between the ANN system and Tc-radionuclide ventriculography (RNV, R = 0.93, SEE = 6.36). The ANN system also performed well in the subset of patients with poor image quality. Endocardial contour detection using artificial neural networks and spatial temporal contour linking allows accurate calculations of ventricular areas from transthoracic echocardiograms and performs well even in images with poor quality. This system could greatly enhance the feasibility, accuracy and reproducibility of calculating cardiac areas to derive left ventricular volumes and ejection fractions.