Summary
Three-dimensional echocardiography of colour Doppler flow developed quickly with the advent of three-dimensional echocardiography. An increasing amount of research has shown that three-dimensional echocardiography of colour Doppler flow is feasible and facilitates measurement of stroke volume and cardiac output, and assessment of heart valve and congenital heart diseases. Although the technique still has some drawbacks that hamper its widespread use, as the technology continues to improve, three-dimensional echocardiography of colour Doppler flow has the potential to serve as a powerful noninvasive clinical tool, aiding physicians in the serial assessment of heart disease and response to intervention. We review the developmental history and the most recent clinical information related to three-dimensional echocardiography of colour Doppler flow.
Résumé
L’échographie tridimensionnelle (3DE) et 3D Doppler couleur (3DE-CDF) se sont développés rapidement depuis l’avènement de l’imagerie tridimensionnelle. Un nombre croissant de données issues de la recherche a montré que le 3DE-CDF était faisable et pouvait permettre d’évaluer le volume d’éjection systolique et le débit cardiaque, d’évaluer les valvulopathies, ainsi que les cardiopathies congénitales. Bien que ces techniques connaissent quelques limites, qui différent une diffusion plus large, avec le développement important technologique, cette méthode sera, à ne pas en douter, un outil clinique d’explorations non invasives puissant pour aider les cliniciens à évaluer de façon répétée les cardiopathies et leurs réponses au traitement. Nous proposons dans cette revue générale de présenter les étapes du développement de l’échographie Doppler couleur tridimensionnelle, ainsi que les implications cliniques potentielles nouvelles et attendues.
Abbreviations
2D
two-dimensional
3D
three-dimensional
2DE
two-dimensional echocardiography
3DE
three-dimensional echocardiography
2DE-CDF
two-dimensional echocardiography of colour Doppler flow
3DE-CDF
three-dimensional echocardiography of colour Doppler flow
LVOT
left ventricular outflow tract
MR
mitral valve regurgitation
RT3DE
real-time three-dimensional echocardiography
Background
One of the greatest achievements of the past two decades in ultrasound imaging of the heart was the development of three-dimensional echocardiography (3DE) . 3DE provides valuable clinical information that gives echocardiographers new levels of confidence in the diagnosis of heart disease. The invention of real-time 3DE (RT3DE) was a technological milestone in the field of 3DE . With the growing availability of 3DE technology, 3DE of colour Doppler flow (3DE-CDF) also developed quickly . The multiple attractive merits of volumetric colour Doppler flow imaging have sparked significant interest among researchers and clinical workers, resulting in satisfactory achievements, some of which have endorsed 3DE-CDF for clinical use by demonstrating its use in heart examination .
The purpose of our paper is to review the developmental history of colour Doppler flow and to update readers with the most recent advancements in 3DE-CDF. Our article also pays close attention to the clinical use of 3DE-CDF.
Development history
During the past few decades, colour Doppler flow imaging has benefited from technical innovations and has become a sophisticated cardiovascular ultrasound technology, which displays blood flow and velocity information on grey-scale images . Colour Doppler flow imaging can provide us with more detailed information on blood flow within the body than any other technique. Employing the hypothesis that there was some kind of regular shape within the heart, 2DE of colour Doppler flow (2DE-CDF) was used widely in the assessment of stroke volume, cardiac output, valve heart disease and congenital heart disease , and has become established as one of diagnostic tools used most frequently in daily clinical practice in cardiology. However, since the advent of colour Doppler flow, most work on colour Doppler flow imaging has been based on 2DE. 2DE-CDF has inherent inaccuracies, because most of the area of the heart where colour Doppler flow works is geometrically complex and changes during the course of the cardiac cycle . Moreover, 2DE-CDF has the limitation of angle dependency, which is not easy to overcome in daily work .
The complex anatomy of cardiac structures requires three-dimensional (3D) spatial orientation of images for a better understanding of structure and function. Twenty years ago, 3DE was developed in order to overcome the drawbacks of 2DE . At an early stage, 3DE was based on 2DE and was completed by reconstruction of multiple two-dimensional (2D) images . The scan head of the 3DE system was rotated around a fixed axis at a set rate for capturing multiple 2D images around the central axis . The multiple 2D image slices were then processed offline to produce a 3D image. Most recently, RT3DE took a big step forward, as a result of the design of an ultrasound transducer with a matrix array. The matrix probe (e.g., Philips, Andover, MA, USA) houses 3000 elements as opposed to 64 in the usual 2D scan head; these are connected to transmit and receive simultaneously, to form a pyramidal-shaped volume that is gated over a cardiac cycle. This volume is then displayed immediately on the system . The simultaneous display of multiple images allows a 3D perspective and the anatomically correct examination of any structure within the volumetric image. With the RT3DE advantages of fewer artefacts, less operator-dependency and lower time-consumption for patients and echosonographers, reconstructive 3DE was replaced quickly by RT3DE .
The development of 3DE also promoted the swift progression of 3DE-CDF from reconstructive 3DE to RT3DE . 3DE volumes containing colour Doppler flow data are acquired in a similar way to the grey-scale volumes of 3DE systems ( Fig. 1 ). Software has been developed to allow calculation of the flow volume in a similar way to 3DE methods and the retained velocity assignments in the datasets. 3DE-CDF has several advantages over 2DE-CDF and overcomes the spatial limitations of the 2DE technique, such as a lack of geometric assumptions and less angle dependency . Volume acquisition by RT3DE-CDF requires only a few beats, and therefore motion and respiratory artefacts are reduced greatly .
Three-dimensional echocardiography of colour Doppler flow enables complete 3D visualization of the blood jet and new ways of assessing blood flow by noninvasive techniques ( Fig. 2 ). Because 3DE-CDF can show the relative spatial location of blood jets and cardiac structures, it can clearly provide 3D information about the actual extension, direction, origin and size of intracardiac flows of regurgitant lesions, shunts and cardiac output . Therefore, combined with the advantages of 3D structure images, 3DE-CDF not only enhances understanding of the complex 3D structure and patterns of intracardiac blood (such as the delineation of valvular leaks, paravalvular leaks and multiple jets), but also may find some complex structures that could not be observed and studied by 2DE-CDF .
Clinical use
Measurement of cardiac output
Accurate measurements of stroke volume and cardiac output are important in both clinical medicine and medical research. In the past, by assuming cylindrical aortic geometry and laminar blood flow at the left ventricular outflow tract (LVOT), 2DE measured the velocity and diameter of the LVOT and then calculated cardiac output . This 2D measurement suffers from inaccuracy, because not only is the LVOT anatomy asymmetrical and sometimes even severely irregular, but also the LVOT diameter changes during the course of the cardiac cycle . Moreover, the peak velocity profiles of LVOT used in 2DE-CDF are not necessarily in the centre and peak velocity must usually be angle corrected; both of these factors tend to lead to an underestimation of cardiac output . 3DE-CDF can eliminate these limitations of 2DE-CDF with the advantages of 3D spatial images and less angle dependency ( Fig. 3 ).
