Fig. 2.1
Simultaneous multiplane mode (X-plane): on the left, a four-chamber apical view focusing on mitral valve. On the right, a plane rotated approximately 90º
Fig. 2.2
Full volume acquisition: This mode allows a large acquisition volume that covers the complete chamber of interest as in this case, the left ventricle
Fig. 2.3
Doppler color 3D: To analyze 3D color Doppler regurgitation jets, it is advisable to crop (see below) to show two long-axis views of the jet, the narrowest and the broadest width of the jet with a short-axis view of the jet at the level of the vena contracta
3D Image Display
There are several methods [1–4]:
Slice rendering
It is possible to obtain multiple simultaneous 2D images from a 3D acquisition that cannot be available in transthoracic 2D echocardiography (2D TTE). Virtually any plane can be achieved either as equidistant parallel slices or as slices rotated around a common axis. The current 3D systems normally show four screens where 3 simultaneous orthogonal 2D planes (coronal, sagittal and transverse or axial) plus a volumetric 3D image can be observed. These views allow accurate measurements of chamber dimensions, valve areas and regurgitant jets (Fig. 2.4).
Fig. 2.4
Slice rendering: An aortic valve is shown from the parasternal long-axis view (upper right), short-axis view (upper left), transverse-cut view (lower left) and the real-time three-dimensional echocardiography volume dataset (lower right)
Volume rendering
It is a method designed to produce images with 3D depth perception. It provides very useful 3D images to assess cardiac valves and complex anatomic structures.
Surface rendering
Another way of visualization of cardiac structures in a 3D scene. To obtain the images, they have to outline either manually or automatically via border detection, the anatomical structure (usually the left ventricle). This type of reconstruction enable us to appreciate geometric shape, and superimpose information on the surface such as timing of contraction (Fig. 2.5) (Video 2.2).
Fig. 2.5 and Video 2.1
Surface rendering: Left ventricle (LV). LV analysis using a semiautomated border detection software allows quantification of LV volumes and ejection fraction. Once having a geometrical description of the LV, surface rendered images of the anatomy can be generated (middle right). Also, a 3D analysis of regional LV wall motion can be obtained (bottom)
Cropping method
This technique allows to remove anatomical structures from the initial data set to focus exclusively on the target anatomy. For example, cropping the left atrium to see the mitral valve from the base of the heart. 3D cropping can be done either during or after data acquisition (Fig. 2.6).
Fig. 2.6
Cropping method: The left atrium has been removed to focus on the mitral valve, showing a flail segment (P2)
3D Artefacts
Several types of artefacts are described [4]:
- (a)
Stitch artefacts
These occur when the mode of acquisition is 3D full volume where subvolumes are recorded and triggered by ECG. The stitch artifacts are displayed when acquired subvolumes do not perfectly merge together and instead the boundaries between the different subvolumes are clearly seen.
Stitch artifacts are caused by irregular rhythms, transductor or patient motion, including respiratory movements (Fig. 2.7).
- (b)
Shadowing or Drop-out artefacts
These are highly echo-reflective structures such as prosthesis, providing areas of drop-out in the rendered image. It also occurs when a suboptimal gain setting is used. For example, when imaging the tricuspid valve, as the three leaflets used to be very thin, if the gain setting is low, then a drop-out may occur.
- (c)
Attenuation artefacts
Gradual deterioration of the signal intensity distal to the volume target because of reduced backscatter and absorption.
- (d)
Reverberations
Multiple reflections between structures giving false echoes within the acquisition volumes.
- (e)
Aberrations
Distortions of the ultrasound beam generating clutter noise as occur within the chamber cavities that obscures the true cardiac wall.
Fig. 2.7
Stich artifact: When using ECG gated stitching of sub-volumes from multiples cardiac cycles (full volume acquisition), there is a danger of getting motion artifacts caused by respiration and heart rate variability as in this case (right image)
3D TTE Protocol Examination
From a clinician point of view, it is more useful to perform a focused 3D TTE examination than a complete 3D TTE study. A focused 3D TTE examination is used to complete a 2D study: this depends on the target anatomical structure, so that a full volume will be acquired if you want to assess left ventricular function. In contrast, if we need to calculate a mitral stenosis area, a 3D zoom acquisition focused on mitral valve will be performed.
Take Home Message
To obtain large volumes with adequate frame rate is the major challenge in 3D TTE.
There are several methods of data acquisition in 3D TTE. Choose the best method suited to the information to be obtained: To assess left ventricular function, choose full volume acquisition. To evaluate mitral or aortic valves, choose zoom acquisition.
Optimize 3D images by adjusting the different settings.
There are also various methods of 3D image display: slice rendering allows accurate measurements of chamber dimensions, valve areas and regurgitant jets. Cropping is very useful to remove anatomical structures to focus exclusively on the target anatomy.
Be aware of the artifacts in 3D TTE, especially drop-out and stich artifacts.
Left Ventricle and Right Ventricle
Left Ventricle
Limitations of 2DE LV Assessment and 3D Advantages
Assessment of the left ventricle (LV) size and function are essential for the study of structural heart diseases. This assessment is predominantly performed using 2D echocardiography (2DE), but 2D echocardiographic data requires assumptions regarding geometric modeling of the LV. The main advantage of 3D imaging is that provides volume and ejection fraction measurements independent of geometric assumptions regarding LV shape [5], which gives more accurate and reproducible chamber quantification compared to other imaging modalities.
Data Acquisition
Apical four-chamber is the preferred view to 3D LV data acquisition.
The full-volume data (data set) should be acquired during a breath hold to minimize the risk for artifacts.
The data set acquisition should be guided by a display of orthogonal views that can be used for simultaneous imaging in two or more planes.
Although there is no general agreement about imaging orientation and display, the apex is showed up and right-sided structures on the left-hand, normally.
Data Analysis
Most 3DE software provides analysis techniques that are fundamentally two-dimensional [6]. In this way, after a few anatomic landmarks in the LV (such as the mitral annulus or apex), 3DE data are usually segmented into several 2D longitudinal planes [1]. Endocardial and epicardial contours can be traced manually [7] or obtained using fully automated contouring algorithms [5]. These algorithms allow the calculation of cavity contours providing a cavity cast of the LV, from which its volume is computed without geometric assumptions [1] (Fig. 2.5) (Video 2.2).
Clinical Application
The application of 3D echocardiography (3DE) is particularly advantageous in these situations:
LV mass or thrombus assessment: 3D imaging provides a 3D impression of the structure.
LV volumes and ejection fraction (LVEF): 3DE is more accurate and reproducible than 2DE, with a high correlation with cardiovascular magnetic resonance reference values [9]. Moreover, 3D is particularly attractive in segmental wall motion assessment. As we explained in “Data analysis” section, 3D imaging provides a full-volume data set to create standard 2D images in which the cut planes are optimized to ensure that they are “on axis”.
Several studies have published 3D echocardiographic LV volumes and LVEF reference values for healthy normotensive subjects. On the basis of weighted averages of three studies, 3D echocardiographic LV volumes were larger than 2D echocardiographic values, and corresponding upper limits of the normal range were [10]:
End-diastolic volumes (EDVs) of 79 mL/m2 for men and 71 mL/m2 for women.
End-systolic volumes (ESVs) of 32 mL/m2 for men and 28 mL/m2 for women.
Ultimately, a large study in a diverse population will be needed to establish normal reference ranges for 3DE for different ethnic groups.
LV mass: Although 3DE is really attractive for LV volume and LVEF assessment, 3D echocardiography overestimates LV mass in comparison with magnetic resonance imaging measurements. The main reason is that endocardial and epicardial contours are usually traced manually [7], but this problem could be solved using automated contouring algorithms [8]. Nonetheless, because 3DE is the only echocardiographic technique that measures myocardial volume without geometric assumptions, this may be used in abnormally shaped ventricles or in patients with asymmetric or localized hypertrophy [10]. No LV mass reference values are available yet.
LV dyssynchrony: In a left ventricle with dyssynchrony there is dispersion in the timing of regional segments, as the diseased segments achieve minimal volume later in systole. The systolic dyssyncrhrony index is calculated from the basal and mid segments of the three standard 2D apical views, and consequently does not reflect the motion pattern of all LV segments in 3D space [11]. In contrast, 3D echocardiography evaluates all LV segments simultaneously, which represents an advantage over 2D echo.
3D TTE LV Assessment Limitations
The main disadvantages of 3D TTE LV assessment are the lower temporal resolution and the lack of published data on normal 3D values [10].
Take Home Message
3D TTE LV volumes and EF measurements are more accurate and reproducible than 2D and should be used when available and feasible.
Apical four-chamber is the preferred view to 3D TTE LV data acquisition.
A display of orthogonal views can be used to guide the 3D TTE LV data set acquisition.
3D data analysis must be done by analysis software, which provides LV measures without geometric assumptions.
The American and European Society of Cardiac Imaging`s consensus document for Cardiac Chamber Quantification by Echocardiography (January, 2015) included normal values for LV parameters obtained with 3D TTE.
Right Ventricle
Limitations of 2DE RV Assessment and 3D Advantages
Because of its peculiar morphology and function, RV global assessment is difficult using 2D echocardiography. In contrast, 3DE enables complete assessment of RV geometry, volumes, and ejection fraction displaying the surfaces of the entire chamber including the inflow, apex, and outflow tracts. In this way, 3DE provides RV assessment without geometric assumptions.
Data Acquisition
Data Analysis
In the 3DE RV data analysis it is critically important to manually define end-diastolic and end-systolic frames using maximal and minimal RV volumes; myocardial trabeculae and moderator band should be included in the cavity. After this manual initialization, the right ventricular endocardial surface is semiautomatically identified in the right ventricular short-axis, four-chamber, and coronal views in both end-systole and end-diastole. The generated 3D surface model of the RV enables the quantitation of right ventricular ESV and ESV, stroke volume, and EF [10].
Clinical Application
Data on RV volumes and function are of diagnostic and prognostic importance in a variety of cardiac diseases [1], including: valve disease, congenital heart disease, pulmonary hypertension, heart failure, etc.
RV volumes: Even though 3DE tends to underestimate RV volumes compared CMR, 3DE volumes values are very similar to those described by cardiac magnetic resonance (CMR). Normal 3D echocardiographic values of RV volumes need to be established in larger groups of subjects, but current published data suggest [10]:
End-diastolic volumes (EDVs) of 87 mL/m2 for men and 74 mL/m2 for women.
End-systolic volumes (ESVs) of 44 mL/m2 for men and 36 mL/m2 for women.
RV Ejection Fraction (RV EF): RVEF assessed by 3D TTE correlates with RV EF by CMR. Roughly, an RV EF of <45% usually reflects abnormal RV systolic function.
This is especially attractive in patients after cardiac surgery (in the absence of marked septal shift), when conventional indices of longitudinal RV function are generally reduced and no longer representative of overall RV performance [10].
3D TTE RV Assessment Limitations
The main limitation is that 3D TTE RV assessment depends on image quality, load, regular rhythm and patient cooperation. As same as in 3D TTE LV assessment, normal 3D echocardiographic values of RV need to be established in larger groups of subjects.
Take Home Message
3D TTE enables complete assessment of RV geometry including the inflow, apex and outflow tract.
RV-focus apical four-chamber is the preferred view to 3D TTE RV data acquisition.
3D TTE RV data analyses includes manually and semiautomatically offline analyses.
The American and European Society of Cardiac Imaging’s consensus document for Cardiac Chamber Quantification by Echocardiography (January, 2015) included normal values for RV parameters obtained with 3D TTE.
Left and Right Atria
Limitations of 2DE LA Assessment and 3D Advantages
3DE left atria (LA) assessment is, as same as LV and RV, more accurate than 2DE compared with CMR [10]. The main advantage of 3D TTE LA and right atria (RA) assessment is that not geometrical assumptions about LA shape are necessary with 3DE.
Data Acquisition
Apical view is the preferred one to 3D TTE atria assessment.
Multibeat full-volume acquisition is needed.
Clinical Application
3DE atria assessment is particularly interesting in:
Diagnosis and management of patients with atrial fibrillation and diastolic dysfunction [10]. For example, one study showed that 3D echocardiography classified enlarged left atria more accurately than 2DE, resulting in fewer patients with undetected atrial enlargement and potentially undiagnosed diastolic dysfunction [12].
Electrophysiologic procedures: Although fluoroscopy is routinely used to localize atrial anatomic landmarks during electrophysiologic procedures, this technique is limited by its 2D projection of complex 3D structures that may render difficult interpretation and analysis [1]. In these cases 3D TTE analyses can be useful.
LA mass or thrombus assessment.
3D TTE LA and RA Assessment Limitations
Because the atria are close to the esophagus, 3D transesophageal echocardiography provides more anatomic data than transthoracic one. Thus, we have a lack of a standardized methodology and limited normative 3D TTE data.
Take Home Message
There is promise that 3D transthoracic echocardiography will improve the accuracy of left atrial measurements. However, no studies to date have evaluated right atrial values.
3D TTE atria assessment is especially useful in electrophysiologic procedures.
Mitral, Aortic, Tricuspid and Pulmonary Valve
Mitral Valve
Anatomy of the Mitral Apparatus and Limitations of 2D–Echocardiography Assessment
The mitral apparatus is formed from the annulus, the leaflets connected by opposing anterolateral and posteromedial commissures, the subvalvular apparatus composed of variable chordae tendineae arrangement with dual papillary muscles, and the left ventricle wall attachments. Three-dimensional echocardiographic imaging modalities are ideal for interrogating the anatomy and function of each of the individual components of the mitral apparatus. It provides additional information in patients with complex mitral valve lesion [1].
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