Dynamic three-dimensional echocardiographic assessment of intracardiac blood flow jets

Clinical application of three-dimensional echocardiography

Echocardiography is one of the most valuable diagnostic tools in cardiology. Technological advances in ultrasound, computer and electronics enables three-dimensional (3-D) imaging to be a clinically viable modality which has significant impact on diagnosis, management and interventional procedures. Since the inception of 3D fully-sampled matrix transthoracic and transesophageal technology it has enabled easier acquisition, immediate on-line display, and availability of on-line analysis for the left ventricle, right ventricle and mitral valve. The use of 3D TTE has mainly focused on mitral valve disease, left and right ventricular volume and functional analysis. As structural heart disease procedures become more prevalent, 3D TEE has become a requirement for preparation of the procedure, intra-procedural guidance as well as monitoring for complications and device function. We anticipate that there will be further software development, improvement in image quality and workflow.

Mitral valve regurgitation and 3D echocardiography

The mitral valve is a complex, dynamic and functional apparatus that can be altered by a wide range of disorders leading to stenosis or regurgitation. Surgical management of mitral valve disease may be difficult. Planned intervention may not always be feasible when the surgeon is faced with complex pathology that cannot be assessed fully by conventional 2D echocardiography. Transthoracic and transesophageal 3D echocardiography can provide a more reliable functional and anatomical assessment of the different valve components and evaluation of its geometry, which can aid the surgeon in planning a more suitable surgical intervention and improve outcomes. Although 3D echocardiography is a new technology, it has proven to be an important modality for the accurate assessment of valvular heart disease and in the future, it promises to be an essential part in the routine assessment of cardiovascular patients.

Atrial septal defects type II: noninvasive evaluation of patients before implantation of an Amplatzer Septal Occluder and on follow-up by magnetic resonance imaging compared with TEE and invasive measurement

The purpose of this study was to evaluate morphological and functional MRI of atrial septal defects (ASD) before and after interventional occlusion by the Amplatzer Septal Occluder (AOC) in comparison to trans-oesophageal echocardiography (TEE), invasive balloon measurement (IVBM) and cardiac catheterisation (QCC). Sixty patients with an ASD type II were enrolled. They underwent TEE, IVBM, QCC and MRI at 1.5T. Cine gradient echo, steady-state free precession sequences and a gradient echo phase contrast sequence were used. In MRI, pulmonary-to-systemic flow ratio (Qp/Qs) was calculated and compared with the QCC Qp/Qs ratio. Qp/Qs ratio in baseline MRI examination was 1.56 +/- 0.29 (range: 1.05-2.2) and in QCC 1.71 +/- 0.30 (range: 1.2-2.4) with a significant correlation (R = 0.65, P < 0.01). Defect size on MRI was 15.3 +/- 7.4 mm (range: 3-30 mm), in TEE 14.3 +/- 4.9 mm (range: 4-24 mm), and the balloon stretched diameter in IVBM was 23.4 +/- 4.2 mm (range: 14-32 mm). Correlation between defect size in MRI vs. TEE was R = 0.67 (P < 0.01) and MRI vs. IVBM was R = 0.77 (P < 0.01). Right ventricular volumes decreased after intervention. MRI is an accurate noninvasive test for diagnosis, planning and follow-up after interventional ASD occlusion using an AOC.

Current Status of Three-Dimensional Color Flow Doppler

Three-dimensional (3D) color Doppler echocardiography is a relatively new noninvasive tool that displays and quantitates regurgitant flow and also enables estimation of cardiac output, stroke volume, pulmonary outflow, and shunt calculations. This article provides an overview of the current methodology of 3D color flow, and its advantages and limitations.

Real-Time Three-Dimensional Echocardiography Using a Novel Matrix Array Transducer

Three-dimensional echocardiography has multiple advantages over two-dimensional echocardiography, such as accurate left ventricular quantification and improved spatial relationships. However, clinical use of three-dimensional echocardiography has been impeded by tedious and time-consuming methods for data acquisition and post-processing. A newly developed matrix array probe, which allows real-time three-dimensional imaging with instantaneous on-line volume-rendered reconstruction, direct manipulation of thresholding, and cut planes on the ultrasound unit may overcome the aforementioned limitations. This report will review current methods of three-dimensional data acquisition, emphasizing the real-time methods and clinical applications of the new matrix array probe.

Dynamic three-dimensional color flow Doppler: an improved technique for the assessment of mitral regurgitation

BACKGROUND

Prior studies have reconstructed mitral regurgitant flow in three dimensions displaying gray scale renditions of the jets, which were difficult to differentiate from surrounding cardiac structures. Recently, a color-coded display of three-dimensional (3D) regurgitant flow has been developed. However, this display was unable to integrate cardiac anatomy, thereby losing spatial information, which made it difficult to determine the jet origin and its spatial trajectory. To overcome this limitation, an improved method of 3D color reconstruction of regurgitant jets obtained from color flow Doppler using a transesophageal approach was developed to allow the combined display of both color flow and gray scale information.

OBJECTIVES

To demonstrate the feasibility of 3D reconstruction of regurgitant mitral flow jets using an improved method of color encoding digital data acquired by transesophageal echocardiography (TEE).

METHODS

We studied 46 patients undergoing a clinically indicated TEE study. All subjects had mitral regurgitation detected on a previous transthoracic study. Atrial fibrillation or poor image quality were not used as exclusion criteria. The 3D study was performed using a commercial ultrasound imaging system with a TEE probe (Sonos 5500, Agilent Technologies). A rotational mode of acquisition was used to collect two-dimensional (2D) color flow images at 3-degree intervals over 180 degrees. Images were processed off line using the Echo-View Software (TomTec Imaging Systems). Volume-rendered 3D color flow jets were displayed along with gray scale information of the adjacent cardiac structures.

RESULTS

Mitral regurgitant flow, displayed in left atrial and two longitudinal orientations, was successfully reconstructed in all patients. The time for acquisition, post-processing, and rendering ranged between 10 and 15 minutes. There were 28 centrally directed jets and 15 eccentric lesions. Eight patients in the study had periprosthetic mitral regurgitant flow.

CONCLUSIONS

Three-dimensional imaging of mitral regurgitant jets is feasible in the majority of patients. This improved technique provides additional information to that obtained from the 2D examination. Particularly, in patients with paravalvular leaks 3D color flow Doppler provides information on the origin and the extent of the dehiscence, as well as insight into the jet direction. In addition, in patients with eccentric mitral regurgitation, this new modality overcomes the inherent limitations of 2D echo Doppler by depicting the full extent of the jet trajectory.

Real-time three-dimensional color doppler evaluation of the flow convergence zone for quantification of mitral regurgitation: Validation experimental animal study and initial clinical experience

BACKGROUND

Pitfalls of the flow convergence (FC) method, including 2-dimensional imaging of the 3-dimensional (3D) geometry of the FC surface, can lead to erroneous quantification of mitral regurgitation (MR). This limitation may be mitigated by the use of real-time 3D color Doppler echocardiography (CE). Our objective was to validate a real-time 3D navigation method for MR quantification.

METHODS

In 12 sheep with surgically induced chronic MR, 37 different hemodynamic conditions were studied with real-time 3DCE. Using real-time 3D navigation, the radius of the largest hemispherical FC zone was located and measured. MR volume was quantified according to the FC method after observing the shape of FC in 3D space. Aortic and mitral electromagnetic flow probes and meters were balanced against each other to determine reference MR volume. As an initial clinical application study, 22 patients with chronic MR were also studied with this real-time 3DCE-FC method. Left ventricular (LV) outflow tract automated cardiac flow measurement (Toshiba Corp, Tokyo, Japan) and real-time 3D LV stroke volume were used to quantify the reference MR volume (MR volume = 3DLV stroke volume - automated cardiac flow measurement).

RESULTS

In the sheep model, a good correlation and agreement was seen between MR volume by real-time 3DCE and electromagnetic (y = 0.77x + 1.48, r = 0.87, P <.001, delta = -0.91 +/- 2.65 mL). In patients, real-time 3DCE-derived MR volume also showed a good correlation and agreement with the reference method (y = 0.89x - 0.38, r = 0.93, P <.001, delta = -4.8 +/- 7.6 mL).

CONCLUSIONS

real-time 3DCE can capture the entire FC image, permitting geometrical recognition of the FC zone geometry and reliable MR quantification.

Quantification of mitral regurgitation orifice area by 3-dimensional echocardiography: comparison with effective regurgitant orifice area by PISA method and proximal regurgitant jet diameter

BACKGROUND

The evaluation of mitral regurgitation (MR) by 3-dimensional (3D) echo has generally been performed by reconstruction of Doppler regurgitant jets but there are little data on measuring anatomic regurgitant orifice area (AROA) directly from 3D mitral valve (MV) reconstructions.

METHODS AND RESULTS

Transoesophageal echo (TOE) 3D images were acquired from 38 unselected patients (age 59+/-11 years, ten in atrial fibrillation) with various degrees of MR. In all patients MV was reconstructed en face from the left atrium (LA) and the left ventricle (LV). AROA was measured by planimetry from 3D pictures and compared to the effective regurgitant orifice area (EROA) by proximal isovelocity surface area and proximal MR jet width from 2D echo. AROA was measured in 95% of patients from LA, 89% from LV and in 84% from both LA and LV. Good correlation was found between EROA and AROA measured from both LA (r=0.97, P<0.0001) and LV (r=0.87, P<0.0001). The mean difference between LA-AROA and EROA was -3.01+/-6.12 mm(2) and -7.18+/-13.84 mm(2) for LV-AROA (P<0.01, respectively). An acceptable correlation was found between the proximal MR jet width and AROA from LA (r=0.71, P<0.0001) and LV perspective (r=0.68, P<0.0001). AROA>or=25 mm(2) differentiated mild MR (graded 1-2) from moderately severe (graded 3-4) with 80-90% accuracy.

CONCLUSIONS

3D TOE provides important quantitative information on both the mechanism and the severity of MR in an unselected group of patients. AROA enables quantification of MR with excellent agreement with the accepted clinical method of proximal flow convergence.

Quantitative assessment of regurgitant flow with total digital three-dimensional reconstruction of color Doppler flow in the convergent region: in vitro validation

BACKGROUND

This study was designed to develop and test a total digital 3-dimensional (3D) color flow map reconstruction for proximal isovelocity surface area (PISA) measurement in the convergent region.

METHODS

Asymmetric flow convergent velocity field was created in an in vitro pulsatile model of mitral regurgitation. Image files stored in the echocardiographic scanner memory were digitally transferred to a computer workstation, and custom software decoded the file format, extracted velocity information, and generated 3D flow images automatically. PISA and volume flow rate were calculated without geometric assumption. For comparison, regurgitant volume was also calculated, using continuous wave Doppler, 2-dimensional (2D), and M-mode color flow Doppler with the hemispheric approach.

RESULTS

Flows from 3D digital velocity profiles showed a closed, excellent relation with actual flow rates, especially for instantaneous flow rate. Regurgitant volume calculated with the 3D method underestimated the actual flow rate by 2.6%, whereas 2D and the M-mode method show greater underestimation (44.2% and 32.1%, respectively).

CONCLUSION

Our 3D reconstruction of color flow Doppler images gives more exact information of the flow convergent zone, especially in complex geometric flow fields. Its total digital velocity process allows accurate measurement of convergent surface area and improves quantitation of valvular regurgitation.

Three-dimensional ultrasound imaging

Ultrasound is an inexpensive and widely used imaging modality for the diagnosis and staging of a number of diseases. In the past two decades, it has benefited from major advances in technology and has become an indispensable imaging modality, due to its flexibility and non-invasive character. In the last decade, research investigators and commercial companies have further advanced ultrasound imaging with the development of 3D ultrasound. This new imaging approach is rapidly achieving widespread use with numerous applications. The major reason for the increase in the use of 3D ultrasound is related to the limitations of 2D viewing of 3D anatomy, using conventional ultrasound. This occurs because: (a) Conventional ultrasound images are 2D, yet the anatomy is 3D, hence the diagnostician must integrate multiple images in his mind. This practice is inefficient, and may lead to variability and incorrect diagnoses. (b) The 2D ultrasound image represents a thin plane at some arbitrary angle in the body. It is difficult to localize the image plane and reproduce it at a later time for follow-up studies. In this review article we describe how 3D ultrasound imaging overcomes these limitations. Specifically, we describe the developments of a number of 3D ultrasound imaging systems using mechanical, free-hand and 2D array scanning techniques. Reconstruction and viewing methods of the 3D images are described with specific examples. Since 3D ultrasound is used to quantify the volume of organs and pathology, the sources of errors in the reconstruction techniques as well as formulae relating design specification to geometric errors are provided. Finally, methods to measure organ volume from the 3D ultrasound images and sources of errors are described.

Three-dimensional echocardiography: historical development and current applications

Three-dimensional (3D) echocardiography facilitates spatial recognition of intracardiac structures, potentially enhancing diagnostic confidence of conventional echocardiography. The accuracy of 3D images has been validated in vitro and in vivo. In vitro, a detail 1.0 mm in dimension and 2 details separated by 1.0 mm can be identified from a volume-rendered 3D image. In vitro 3D volume measurements are underestimated by approximately 4.0 mL. In vivo, left ventricular volume measurements correlate highly with both cineventriculography (limits of agreement +/-18 mL for end diastole and +/-10 mL for end systole) and magnetic resonance imaging, including measurements for patients with functionally single ventricles. Studies on congenital heart lesions have shown good accuracy and good reproducibility of dynamic "surgical" reconstructions of septal defects, aortoseptal continuity, atrioventricular junction, and both left and right ventricular outflow tract morphology. Transthoracic 3D echocardiography was shown feasible in 81% to 96% of patients with congenital heart defects and provided additional information to that available from conventional echocardiography in 36% of patients, mainly in more detailed description of mitral valve morphology, aortoseptal continuity, and atrial septum. In patients with mitral valve insufficiency, 3D echocardiography was shown to be accurate in the quantification of the dynamic mechanism of mitral regurgitation and in the assessment of mitral commissures in patients with mitral stenosis. This includes not only valve tissue reconstruction but also color flow intracardiac jets. Three-dimensional reconstructions of the aortic valve were achieved in 77% of patients, with an accuracy of 90%. In conclusion, the role of 3D echocardiography, which continues to evolve, shows promise in the assessment of congenital and acquired heart disease.

Quantitative assessment of severity of ventricular septal defect by three-dimensional reconstruction of color Doppler-imaged vena contracta and flow convergence region

BACKGROUND

The aim of the present study was to investigate the feasibility and potential value of the computer-controlled, 3D, echocardiographic reconstruction of the color Doppler-imaged vena contracta (CDVC) and the flow convergence (FC) region as a means of accurately and quantitatively estimating the severity of a ventricular septal defect (VSD).

METHODS AND RESULTS

We performed a 3D reconstruction of the CDVC and the FC region in 19 patients with an isolated VSD using an ultrasound system interfaced with a Tomtec computer. The variable asymmetric geometry of the CDVC and the FC region could be 3D-visualized in all patients. The 3D-measured areas of CDVC correlated well with volumetric measurements of the severity of VSD (r=0.97, P:<0.001). Regression analysis between the shunt flow rate (calculated from the product of the area of CDVC and the continuous Doppler-derived velocity time integral) and the corresponding reference results (calculated by cardiac catheterization) demonstrated a close correlation (r=0.95, P:<0.001). There was also a good correlation between shunt flow rates calculated using the conventional 2D, 1-axis measurement of the FC isovelocity surface area with the hemispheric assumption (r=0.95, P:<0.001); shunt flow rates calculated using 3D, 3-axis measurements of the FC region (r=0.97, P:<0.01); and reference results by cardiac catheterization. However, the 2D method substantially underestimated the actual shunt flow rate.

CONCLUSIONS

The 3D reconstruction of the CDVC and the FC region may aid in quantifying the severity of VSD.

Three-dimensional color Doppler reconstruction of intracardiac blood flow in patients with different heart valve diseases

An improved perception of the magnitude and dynamics of intracardiac flow disturbances has been made possible by the advent of 3-dimensional (3-D) color Doppler, a new diagnostic procedure developed at our institution. This study describes the new insights derived from 3-D reconstruction of color Doppler flow patterns in patients with different heart valve diseases. The color Doppler flow data from 153 multiplanar transesophageal or transthoracic echocardiographic examinations has been obtained from 133 patients with heart valve disease; 73 patients had mitral regurgitation, 15 had mitral stenosis, 18 had aortic regurgitation, 26 had aortic stenosis, and 21 patients had tricuspid regurgitation. Four patients had pulmonary regurgitation associated with mitral valve disease. The 3-D reconstructions of color Doppler flow signals were accomplished by means of the "Heidelberg Raytracing model," developed at our institution. The 3-D color Doppler reconstructions were obtained in all patients. The 3-D images revealed for the first time the complex spatial distribution of the blood flow abnormalities in the heart chambers caused by different heart valve diseases. New patterns of intracardiac blood flow disturbances were observed and classified. Three-dimensional color Doppler provides a unique noninvasive method that can be easily applied for studying intracardiac blood flow disturbances in clinical practice.

Comparison of septal defects in 2D and 3D echocardiography using active contour models

Three-dimensional ultrasound is emerging as a viable resource for the imaging of internal organs. Quantitative studies correlating ultrasonic volume measurements with MRI data continue to validate this modality as a more efficient alternative for 3D imaging studies. However, the processing required to form 3D images from a set of 2D images may result in a loss of spatial resolution and may give rise to artifacts. This paper examines a method of automatic feature extraction and data quantification in 3D data sets as compared with original 2D data. This work will implement an active contour algorithm to automatically extract the endocardial borders of septal defects in echocardiographic images, and compare the size of the defects in the original 2D images and the 3D data sets.

Three-dimensional color Doppler flow reconstruction and its clinical applications

The visualization and quantification of intracardiac blood flow have always been a challenging task for the cardiologist. The advent of color Doppler flow imaging substantially enhanced the clinical diagnosis of heart valve disease. Three-dimensional (3-D) color Doppler, a new diagnostic procedure, refines the diagnostic value of color Doppler by providing unique spatial and temporal information about the actual extension, direction, origin, and size of intracardiac flows. Here, we describe the procedure for 3-D color Doppler reconstruction of intracardiac blood flow velocities and reveal the varied findings in different heart pathologies that cause blood flow disturbances. An automated procedure for the segmentation of turbulent and laminar flows, which allows for the measurement of mitral regurgitant jet volumes, is one of the first 3-D quantitative approaches to the clinical assessment of mitral valve regurgitation. The major technical advances of this procedure include the direct use of digital color Doppler velocity data and an automatic voxel count of the turbulent jet flows. Three-dimensional color Doppler not only can disclose the spatial complex geometry of intracardiac blood flow disturbances but also can quantitatively assess the severity of mitral valve regurgitation.

Three-dimensional transesophageal echocardiography (TEE) and other future directions

As faster imaging systems enter the market, three-dimensional echocardiography is gearing up to become a useful tool in assisting the clinician to image the heart in many innovative projections. What started out as a novel idea of displaying a three-dimensional anatomic picture of the heart now provides a multitude of views of the heart and its structures. Information gained from anatomic and dynamic data has helped clinicians and surgeons in making clinical decisions. In the future, this imaging modality may become a routine imaging modality for assessing cardiac pathology and may serve to increase understanding of the dynamics of the heart.

Three-dimensional echocardiography using a muliplane transesophageal probe: the clinical applications

The use of multiplane transesophageal echocardiography has provided three-dimensional image sets of the heart from multiple two-dimensional images with high-image quality through rotation of the transducer without changing its position (rotational scanning). We discuss the methods, clinical applications, and current limitations of this three-dimensional technique.

Volumetric blood flow measurement with the use of dynamic 3-dimensional ultrasound color flow imaging

We describe a new method for measuring blood volume flow with the use of freehand dynamic 3-dimensional echocardiography. During 10 to 20 cardiac cycles, the ultrasonographic probe was slowly tilted while its spatial position was continuously recorded with a magnetic position sensor system. The ultrasonographic data were acquired in color flow imaging mode, and the separate raw digital tissue and Doppler data were transferred to an external personal computer for postprocessing. From each time step in the reconstructed 3-dimensional data, one cross-sectional slice was extracted with the measured and recorded velocity vector components perpendicular to the slice. The volume flow rate through these slices was found by integrating the velocity vector components, and was independent of the angle between the actual flow direction and the measured velocity vector. Allowing the extracted surface to move according to the movement of anatomic structures, an estimate of the flow through the cardiac valves was achieved. The temporal resolution was preserved in the 3-dimensional reconstruction, and with a frame rate of up to 104 frames/s, the reconstruction jitter artifacts were reduced. Examples of in vivo blood volume flow measurement are given, showing the possibilities of measuring the cardiac output and analyzing blood flow velocity profiles.

Mitral regurgitation: comprehensive assessment by echocardiography

Two-dimensional and Doppler echocardiography have become the major modalities for the assessment of mitral regurgitation. The combined use of these techniques provides information regarding the morphology of the valvular apparatus as well as the severity of regurgitation. Transesophageal and three-dimensional echocardiography provide a more-detailed evaluation of valve morphology, which can be valuable in determining suitability for valve repair. In patients with severe mitral regurgitation, echocardiographic assessment of ventricular size and function plays a critical role in determining the optimal timing of surgery.

Developments in cardiac ultrasound

This article gives an overview of recent developments in cardiac ultrasound for the general hospital physician. It discusses contrast echocardiography, harmonic imaging, three-dimensional echocardiography, Doppler tissue imaging and perfusion imaging and give an outlook on future perspectives.

Flow convergence flow rates from 3-dimensional reconstruction of color Doppler flow maps for computing transvalvular regurgitant flows without geometric assumptions: An in vitro quantitative flow study

OBJECTIVE

This study was designed to develop and test a 3-dimensional method for direct measurement of flow convergence (FC) region surface area and for quantitating regurgitant flows with an in vitro flow system.

BACKGROUND

Quantitative methods for characterizing regurgitant flow events such as flow convergence with 2-dimensional color flow Doppler imaging systems have yielded variable results and may not be accurate enough to characterize those more complex spatial events.

METHOD

Four differently shaped regurgitant orifices were studied: 3 flat orifices (circular, rectangular, triangular) and a nonflat one mimicking mitral valve prolapse (all 4 orifice areas = 0.24 cm(2)) in a pulsatile flow model at 8 to 9 different regurgitant flow rates (10 to 50 mL/beat). An ultrasonic flow probe and meter were connected to the flow model to provide reference flow data. Video composite data from the color Doppler flow images of the FC were reconstructed after computer-controlled 180 degrees rotational acquisition was performed. FC surface area (S cm(2)) was calculated directly without any geometric assumptions by measuring parallel sliced flow convergence arc lengths through the FC volume and multiplying each by the slice thickness (2.5 to 3.2 mm) over 5 to 8 slices and then adding them together. Peak regurgitant flow rate (milliliters per second) was calculated as the product of 3-dimensional determined S (cm(2)) multiplied by the aliasing velocity (centimeters per second) used for color Doppler imaging.

RESULTS

For all of the 4 shaped orifices, there was an excellent relationship between actual peak flow rates and 3-dimensional FC-calculated flow rates with the direct measurement of the surface area of FC (r = 0.99, mean difference = -7.2 to -0.81 mL/s, % difference = -5% to 0%), whereas a hemielliptic method implemented with 3 axial measurements of the flow convergence zone from 2-dimensional planes underestimated actual flow rate by mean difference = -39.8 to -18.2 mL/s, % difference = -32% to -17% for any given orifice.

CONCLUSIONS

Three-dimensional reconstruction of flow based on 2-dimensional color Doppler may add quantitative spatial information, especially for complex flow events. Direct measurement of 3-dimensional flow convergence surface areas may improve accuracy for estimation of the severity of valvular regurgitation.

Pediatric echocardiography: applications and limitations

Echocardiography is an extraordinarily useful imaging technique in fetuses, infants, children, and adolescents. Recent technologic innovations have expanded its versatility in the pediatric population. However, limited societal resources, limitations inherent to ultrasound imaging, and numerous imaging options even within the field of pediatric echocardiography necessitate the discriminate and thoughtful use of echocardiography in children. The clinical assessment remains a critical prelude to echocardiographic examination of the pediatric cardiovascular system.

Three-dimensional color Doppler: a clinical study in patients with mitral regurgitation

OBJECTIVES

The purpose of this study was to assess the clinical feasibility of three-dimensional (3D) reconstruction of color Doppler signals in patients with mitral regurgitation.

BACKGROUND

Two-dimensional (2D) color Doppler has limited value in visualizing and quantifying asymmetric mitral regurgitation. Clinical studies on 3D reconstruction of Doppler signals in original color coding have not yet been performed in patients. We have developed a new procedure for 3D reconstruction of color Doppler.

METHODS

We studied 58 patients by transesophageal 3D echocardiography. The jet area was assessed by planimetry and the jet volumes by 3D Doppler. The regurgitant fractions, the volumes, and the angiographic degree of mitral regurgitation were assessed in 28 patients with central jets and compared with those of 30 patients with eccentric jets.

RESULTS

In all patients, jet areas and jet volumes significantly correlated with the angiographic grading (r = 0.73 and r = 0.90), the regurgitant fraction (r = 0.68 and r = 0.80) and the regurgitant volume (r = 0.66 and r = 0.90). In patients with central jets, significant correlations were found between jet area and angiography (r = 0.86), regurgitant fraction (r = 0.64) and regurgitant volume (r = 0.78). No significant correlations were found between jet area and angiography (r = 0.53), regurgitant fraction (r = 0.52) and regurgitant volume (r = 0.53) in the group of patients with eccentric jets. In contrast, jet volumes significantly correlated with angiography (r = 0.90), regurgitant fraction (r = 0.75) and regurgitant volume (r = 0.88) in the group of patients with eccentric jets.

CONCLUSIONS

Three-dimensional Doppler revealed new images of the complex jet geometry. In addition, jet volumes, assessed by an automated voxel count, independent of manual planimetry or subjective estimation, showed that 3D Doppler is also capable of quantifying asymmetric jets.

Evolving era of multidimensional medical imaging

Currently, computer-assisted imaging can visualize very fast or very slow nonvisible motion events. We can create measurable geometric representations of physiology, including transformation, blood flow velocity, perfusion, pressure, contractility, image features, electricity, metabolism, and a vast number of other constantly changing parameters. The greatest attribute is the ability to present physiologic phenomena as easily understood geometric images more suited to the human's four-dimensional comprehension of reality. The key research challenges are to discover new visual metaphors for representing information, understand the analysis tasks that they support, and associate relevant information to create new information.

Three-dimensional reconstruction of the color Doppler-imaged vena contracta for quantifying aortic regurgitation: studies in a chronic animal model

BACKGROUND

The purpose of this study was to investigate the use of 3-dimensional (3D) reconstruction of color Doppler flow maps to image and extract the vena contracta cross-sectional area to determine the severity of aortic regurgitation (AR) in an animal model. Evaluation of the vena contracta with 2-dimensional imaging systems may not be sufficiently robust to fully characterize this region, which may be asymmetrically shaped.

METHODS AND RESULTS

In 6 sheep with surgically induced chronic AR, 18 hemodynamically different states were studied. Instantaneous regurgitant flow rates were obtained by aortic and pulmonary electromagnetic flowmeters (EMFs) as reference standards, and aortic regurgitant effective orifice areas (EOAs) were determined from EMF regurgitant flow rates divided by continuous-wave (CW) Doppler velocities. Composite video data for color Doppler imaging of the aortic regurgitant flows were transferred into a TomTec computer after computer-controlled 180 degrees rotational acquisition. After the 3D data transverse to the flow jet were sectioned, the smallest proximal jet cross section was identified for direct measurement of the vena contracta area. Peak regurgitant flow rates and regurgitant stroke volumes were calculated as the product of these areas and the CW Doppler peak velocities and velocity-time integrals, respectively. There was an excellent correlation between the 3D-derived vena contracta areas and reference EOAs (r=0.99, SEE=0.01 cm2) and between 3D and reference peak regurgitant flow rates and regurgitant stroke volumes (r=0.99, difference=0.11 L/min; r=0.99, difference=1.5 mL/beat, respectively).

CONCLUSIONS

3D-based determination of the vena contracta cross-sectional area can provide accurate quantification of the severity of AR.

Three-dimensional echocardiographic analysis of valve anatomy as a determinant of mitral regurgitation after surgery for atrioventricular septal defects

Mitral regurgitation (MR) is a significant complication after atrioventricular septal defect (AVSD) surgery. The relation of the valve leaflet morphology and the MR mechanism remains a conundrum. Two-dimensional echocardiography depicts leaflet edges, whereas volume-rendered 3-dimensional echocardiography provides direct visualization of the surface areas of the mitral valve leaflets. This study examines the relation of mitral valve anatomy as determined by 3-dimensional echocardiography with MR origins in patients after AVSD repair. Twenty-seven patients with AVSD surgery and Doppler color MR were prospectively enrolled (median age was 5 years and 16 patients had Down syndrome). Doppler color flow imaging of the MR jet and 3-dimensional echocardiography of the mitral valve were performed with a probe in the transthoracic or transesophageal position. Enface 3-dimensional views of the mitral valve from the left atrium were reconstructed. Analysis of the 3-dimensional data was possible in 21 of the 27 patients. Mean area ratios of the 3 mitral leaflets were calculated (superior 40 +/- 7%, inferior 35 +/- 5%, mural 25 +/- 6%). Both intra and interobserver variability on the area measurements were <5%. In 12 patients (group 1) the jet appeared to emanate medially from the region of coaptation of the superior and inferior components of the anterior leaflet. In 9 patients (group 2) the jet emanated more laterally from the region toward the mural leaflet. The area ratios of the inferior leaflet were 32 +/- 4% in group 1 and 38 +/- 6% in group 2 (p = 0.02). The area ratios of the mural leaflet were 28 +/- 5% in group 1 and 21 +/- 5% in group 2 (p = 0.007). The superior leaflet area ratio was not different in groups 1 and 2, 40 +/- 9% and 41 +/- 6%, respectively. Three-dimensional echocardiography provides new insight into the anatomic determinants of MR following AVSD surgery.

Three-dimensional color Doppler: a new approach for quantitative assessment of mitral regurgitant jets

Color Doppler echocardiography does not provide adequate information about the severity of mitral regurgitation in patients with eccentric mitral regurgitation. We have developed a new procedure for 3-dimensional (3D) color Doppler reconstruction and for segmentation of regurgitant jets. The volume of regurgitant jets was compared with jet area in 63 patients with mitral regurgitation. Mitral regurgitation was assessed by angiography, regurgitant fraction and volume by pulsed Doppler, JA by planimetry, and JV by 3-dimensional Doppler. Twenty-eight patients with central jets were compared with 35 patients with eccentric jets. In the patients with eccentric jets, JV showed significant correlations with regurgitant volume (r = 0.90; P <.01) and regurgitant fraction (r = 0.76; P < .01) and was able to separate groups with different degrees of mitral regurgitation (P <.01). Three-dimensional Doppler revealed origin, direction, and spatial spreading of complex jet geometry. JV, a new parameter of mitral regurgitation, was also capable of quantifying asymmetrical jets.

Three-dimensional color Doppler for assessing mitral regurgitation during valvuloplasty

OBJECTIVE

Transesophageal color Doppler (or 2D Doppler) is the most widely used technique for intraoperative assessment of mitral valve repair. However, the most severe mitral regurgitations produce eccentric jet flows which cannot be assessed by 2D imaging. Up to now the indications for surgical intervention and intraoperative decisions after valve repair have been based on 2D Doppler examinations. Aim of this study was to compare conventional 2D Doppler to three-dimensional (3D) Doppler for assessing residual regurgitation in patients after mitral valvuloplasty.

METHODS

Twenty-four patients were referred to surgery for mitral valve repair. They underwent transesophageal echocardiography and 3D data acquisition during mitral valve reconstruction. Conventional assessment of mitral valve regurgitation, measured by color Doppler jet area, was compared to the volume of regurgitant jets obtained by 3D Doppler. Regurgitant volume and fraction were measured by pulsed Doppler and two-dimensional echocardiography. The 3D reconstructions of color Doppler data were accomplished by means of the 'Heidelberg Raytracing Algorithm' developed at our institution.

RESULTS

The jet areas did not show any significant correlation to the regurgitant fraction (r = 45; P = NS) or regurgitant volumes (r = 0.40; P = NS). In contrast the jet volumes correlated significantly to regurgitant fraction (r = 0.71; P < 0.01) and regurgitant volume (r = 0.85; P < 0.01). The reproducibility analysis of repeated jet volume and jet area measurements also showed that the parameter jet volume has a lower variability and higher agreement of repeated measurements than jet area.

CONCLUSIONS

Three-dimensional color Doppler flow imaging revealed the complex geometry of eccentric regurgitant jets and showed that the assessment of mitral regurgitation, based on conventional 2D Doppler, can be misleading. This new technique has a great potential for becoming a reference method for assessing mitral valve repair.

Quantitative assessment of chronic aortic regurgitation with 3-dimensional echocardiographic reconstruction: comparison with electromagnetic flowmeter measurements

Two-dimensional echocardiography and color Doppler are useful in the qualitative assessment of aortic regurgitation. However, color Doppler planar methods are not accurate in quantifying regurgitant flow, in part because of the complex geometry of aortic regurgitant flow events. Three-dimensional echocardiographic reconstruction is a new technique that provides dynamic 3-dimensional images of intracardiac color flow jets. We sought to determine whether the measurement of aortic regurgitant jet volume by 3-dimensional echocardiography correlated with the true regurgitant volume, measured by electromagnetic flowmeter in vivo, to accurately reflect the severity of aortic regurgitation. We performed volume-rendered 3-dimensional echocardiography in 6 sheep with surgically induced chronic eccentric aortic regurgitation. We obtained a total of 22 aortic regurgitation states by altering loading conditions. Instantaneous regurgitant flow rates were obtained by aortic and pulmonary electromagnetic flowmeters. The maximum aortic regurgitant jet volume by 3-dimensional echocardiography and the maximum jet area by 2-dimensional echocardiography were measured and compared with electromagnetic flowmeter data. By electromagnetic flowmeter, aortic regurgitant flow rate varied from 0.14 to 3.1 L/min (mean 1. 25 +/- 0.78); aortic regurgitant stroke volume varied from 1 to 34 mL/beat (mean 12 +/- 8), and regurgitant fraction varied from 3% to 42% (mean 25% +/- 12%). The maximum jet volume by 3-dimensional echocardiography correlated very well with the aortic regurgitant stroke volume (r = 0.92; P <.0001), with the mean regurgitant flow rate (r = 0.87; P <.0001), and with the regurgitant fraction (r = 0. 87; P <.0001) derived from electromagnetic flowmeter. Both intraobserver and interobserver variability on the measurement of the jet volume by 3-dimensional echocardiography were excellent (r = 0.98; P <.0001 and r = 0.90; P <.001, respectively). The maximum jet area by 2-dimensional echocardiography did not correlate with the aortic regurgitant stroke volume (r = 0.41; P = not significant) and related poorly with the regurgitant fraction (r = 0.52; P <.05) by electromagnetic flowmeter. Dynamic 3-dimensional echocardiography can allow better determination of the geometry of the aortic regurgitant jet and may assist of quantifying the severity of aortic regurgitation.

Assessment of mitral regurgitant jets by three-dimensional color Doppler

BACKGROUND

Color Doppler echocardiography is a standard technique for assessing mitral regurgitation before and after mitral valvuloplasty. Mitral valve prolapse produces complex eccentric jet flows that cannot be visualized and measured by two-dimensional color Doppler echocardiography. The aim of this study was to evaluate the clinical impact of three-dimensional color Doppler echocardiography, a new technique developed at our institution, for assessing mitral regurgitation.

METHODS

Forty-five patients with mitral regurgitation underwent intraoperative transesophageal echocardiography and three-dimensional Doppler data acquisition. The grade of mitral regurgitation was assessed by angiography. The jet areas were calculated by planimetry from conventional color Doppler; the jet volumes were obtained by three-dimensional Doppler data.

RESULTS

New patterns of mitral regurgitant flows were recognized according to the origin, direction, and spatial spreading into the left atrium. Conventional jet areas failed to separate the groups of patients with different degrees of regurgitation, whereas the jet volumes were able to divide patients with different regurgitation grades. No significant correlation was found between jet area and angiographic grading (r = 0.63, p = NS). Jet volumes were significantly correlated to angiography (r = 0.89, p < 0.001).

CONCLUSIONS

Three-dimensional color Doppler echocardiography revealed new patterns of regurgitant flow and allowed a more accurate semiquantitative assessment of complex asymmetrical regurgitant jets.

Three-dimensional ultrasound imaging

The objective of this article is to provide scientists, engineers and clinicians with an up-to-date overview on the current state of development in the area of three-dimensional ultrasound (3-DUS) and to serve as a reference for individuals who wish to learn more about 3-DUS imaging. The sections will review the state of the art with respect to 3-DUS imaging, methods of data acquisition, analysis and display approaches. Clinical sections summarize patient research study results to date with discussion of applications by organ system. The basic algorithms and approaches to visualization of 3-D and 4-D ultrasound data are reviewed, including issues related to interactivity and user interfaces. The implications of recent developments for future ultrasound imaging/visualization systems are considered. Ultimately, an improved understanding of ultrasound data offered by 3-DUS may make it easier for primary care physicians to understand complex patient anatomy. Tertiary care physicians specializing in ultrasound can further enhance the quality of patient care by using high-speed networks to review volume ultrasound data at specialization centers. Access to volume data and expertise at specialization centers affords more sophisticated analysis and review, further augmenting patient diagnosis and treatment.

Three-dimensional fetal echocardiography

The complex anatomy and dynamics of the heart make it a challenging organ to image. The fetal heart is particularly difficult because it is located deep within the mother's abdomen and direct access to electrocardiographic information is difficult. Thus more complex imaging and analysis methods are necessary to obtain information regarding fetal cardiac anatomy and function. This information can be used for medical diagnosis, model development and theoretical validation. The objective of this article is to provide scientists and engineers with an overview of three-dimensional fetal echocardiography.

Clinical application of transthoracic volume-rendered three-dimensional echocardiography in the assessment of mitral regurgitation

Two-dimensional echocardiography (2-DE) and Doppler methods are generally used for assessing mechanisms and severity of mitral regurgitation (MR). Recently, 3-dimensional echocardiography (3-DE) has been applied successfully in various cardiac disorders, but its value in evaluating the mechanism and the severity of MR are not known. We studied 30 patients with MR using 2-DE and 3-DE. Volume-rendered gray-scale 3-DE images of the mitral valve apparatus and MR jets were reconstructed. Maximal volume of the MR jet by 3-DE was compared with mitral regurgitant volume and fraction, regurgitant jet area and the ratio of jet area to left atrial area, and semiquantitative grading derived from 2-DE methods. Our results demonstrated that 3-DE aided in a better depiction of the mitral apparatus and its abnormalities in 70% of the patients. The origin, direction, and morphology of the MR jet were better delineated in 3-DE volumetric display. Quantitative analysis, however, showed only a weak to moderate correlation between 3-DE maximal MR jet volume and 2-DE mitral regurgitant volume (y = 0.5x + 11.4, r = 0.7), regurgitant fraction (y = 0.5x + 8.2, r = 0.65), mitral regurgitant jet area (y = 0.2x + 5, r = 0.51), jet area to left atrial area ratio (y = 0.53x + 7.6, r = 0.54), and semiquantitative grading of MR (y = 9.1x - 1.8, r = 0.74). In conclusion, 3-DE aids in a better understanding of the mechanisms of MR and morphology of the regurgitant jets. Its quantitative ability, when reconstruction of the jet alone is used, may be limited.

Three-dimensional echocardiography: clinical relevance and application

Three-dimensional (3D) echocardiography has recently become a practical reality. It is now practicable to perform 3D echocardiography using transthoracic and transesophageal acoustic windows both in adults and children. The unique image projections that 3D echocardiography yields appear to have enormous potential for displaying intracardiac anatomy in exquisite detail. An important aspect of 3D echocardiography is its ability to supply accurate quantitative data without the use of geometric assumptions. In particular, coupled to contrast ultrasound agents, 3D echocardiography could be valuable in the assessment of myocardial perfusion abnormalities. Early clinical experience suggests that 3D echocardiography is likely to play a valuable role in the evaluation of various cardiac disorders, especially in cardiac surgery. In this section, we will review the use of volume-rendered 3D echocardiography in the diagnosis and assessment of cardiac disorders with particular emphasis on the clinical application of this new methodology.

Three-Dimensional Echocardiography of the Aortic Valve: Feasibility, Clinical Potential, and Limitations

OBJECTIVES: The purpose of our study was to assess the feasibility and potential clinical utility of three-dimensional echocardiography for evaluation of the aortic valve. BACKGROUND: The value of three-dimensional echocardiographic assessment of the aortic valve has not been established yet. METHODS: The study group comprised 32 patients (11 women, 21 men), mean age 56.1 (range 20-82). Seven morphologically normal valves, 5 homografts, 6 mechanical prostheses, and 14 valves of abnormal morphology were evaluated. Images were acquired during a routine multiplane transesophageal echocardiographic examination (rotational scan with 2 degrees interval, respiration, and electrocardiogram [ECG] gating) and postprocessed off-line. A selection of reconstructed cutplanes (anyplane mode) and volume-rendered three-dimensional views of aortic valve anatomy were analyzed by two observers and compared with two-dimensional echocardiography findings. RESULTS: The quality of reconstructions was scored excellent when permitting unrestricted assessment of aortic valve anatomy with optimized planimetric measurements (19 patients, 59%), adequate when aortic valve was partially visualized (7 patients, 22%), or inadequate when no assessment was possible (6 patients, 19%, including 5 with prosthetic valves). Three-dimensional echocardiography provided additional information in ten (31%) patients as compared with the two-dimensional echocardiographic findings. CONCLUSIONS: It can be concluded that three-dimensional echocardiographic reconstruction of the aortic valve is feasible, with excellent or adequate quality in 81% of patients, more frequently in native than in prosthetic valves, P < 0.05. Morphologic information additional to that provided by two-dimensional echocardiography is obtained in a significant proportion of patients.

Feasibility, accuracy, and incremental value of intraoperative three-dimensional transesophageal echocardiography in valve surgery

In this prospective trial, intraoperative 2-dimensional (2-D) and 3-dimensional (3-D) transesophageal echocardiography (TEE) examinations were performed on 60 consecutive patients undergoing cardiac valve surgery. Both 2-D (including color flow and Doppler data) and 3-D images were reviewed by blinded observers, and major valvular morphologic findings recorded. In vivo morphologic findings were noted by the surgeon and all explanted valves underwent detailed pathologic examination. To test reproducibility, 6 patients also underwent 3-D TEE 1 day before surgery. A total of 132 of 145 attempted acquisitions (91%) were completed with a mean acquisition time of 2.8 +/- 0.2 minutes. Acquisition time was significantly shorter in patients with regular rhythms. Reconstructions were completed in 121 of 132 scans (92%) and there was at least 1 good reconstruction in 56 of 60 patients (93%). Mean reconstruction time was 8.6 +/- 0.7 minutes. Mean effective 3-D time, which was the time taken to complete an acquisition and a clinically interpretable reconstruction, was 12.2 +/- 0.8 minutes. Intraoperative 3-D echocardiography was clinically feasible in 52 patients (87%). Three-D echocardiography detected most of the major valvular morphologic abnormalities, particularly leaflet perforations, fenestrations, and masses, confirmed on pathologic examination. Three-D echocardiography predicted all salient pathologic findings in 47 patients (84%) with good quality images. In addition, in 15 patients (25%), 3-D echocardiography provided new additional information not provided by 2-D echocardiography, and in 1 case, 3-D echocardiographic findings resulted in a surgeon's decision to perform valve repair rather than replacement. In several instances, 3-D echocardiography provided complementary morphologic information that explained the mechanism of abnormalities seen on 2-D and color flow imaging. In the reproducibility subset, preoperative and intraoperative 3-D imaging detected a similar number of findings when compared with pathology. Thus, in routine clinical intraoperative settings, 3-dimensional TEE is feasible, accurately predicts valve morphology, and provides additional and complementary valvular morphologic information compared with conventional 2-D TEE, and is probably reproducible.

Direct measurement of three-dimensionally reconstructed flow convergence surface area and regurgitant flow in aortic regurgitation: in vitro and chronic animal model studies

BACKGROUND

Evaluation of flow convergence (FC) with two-dimensional (2D) imaging systems may not be sufficiently accurate to characterize these often asymmetric, complex phenomena. The aim of this study was to validate a three-dimensional (3D) method for determining the severity of aortic regurgitation (AR) in an experimental animal model.

METHODS AND RESULTS

In six sheep with surgically induced chronic AR, 20 hemodynamically different states were studied. Instantaneous regurgitant flow rates were obtained by aortic and pulmonary electromagnetic flow meters. Video composite data of color Doppler flow mapping images were transferred into a TomTec computer after computer-controlled 180 degrees rotational acquisition. Direct measurement of the 3D reconstructed FC surface areas as well as measurements of FC areas estimated with 2D methods with hemispherical and hemielliptical assumptions were performed, and values were multiplied by the aliasing velocity to obtain peak regurgitant flow rates. There was better agreement between 3D and electromagnetically derived flow rates than there was between the 2D and the reference values (r=.94, y=1.0x-0.16, difference=0.02 L/min for the 3D method; r=.80, y=1.6x-0.3, difference=1.2 L/min for the 2D hemispherical method; r=.75, y=0.90x+0.2, difference=-0.20 L/min for the 2D hemielliptical method).

CONCLUSIONS

Without any geometrical assumption, the 3D method provided better delineation of the FC zones and direct measurements of FC surface areas, permitting more accurate quantification of the severity of AR than the 2D methods.