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Principles of Transthoracic Imaging Acquisition : The Standard Adult Transthoracic Echocardiographic Examination


Introduction

In the adult two-dimensional (2D) transthoracic echocardiographic (TTE) examination, a standard series of cross-sectional anatomical views are recommended by the American Society of Echocardiography (ASE). Each echocardiographic view is described using three aspects of the examination, namely (1) the transducer positioned at a specified anatomical “window” on or near the thorax, (2) the cardiac scan plane transected by the transducer beam, and (3) the anatomical structure or region of interest ( Fig. 8.1 ). The 2D TTE examination is the basis for the comprehensive assessment of cardiac structure and function ( Figs. 8.2–8.21 ; see also Fig. 8.1 ).

FIG. 8.1, Graphical summary of the standard examination protocol and nomenclature of the two-dimensional (2D) transthoracic echocardiographic views (American Society of Echocardiography [1980]). Note the transducer scan planes and cross-sectional anatomical planes.

FIG. 8.2, The standard recommended transducer positions in transthoracic echocardiography. PLAX, Parastemal long-axis; PSAX, Parastemal short-axis.

FIG. 8.3, The orthogonal anatomical imaging planes and the echocardiographic imaging planes compared.

FIG. 8.4, The standard orthogonal cardiac imaging planes and cross-sectional projections.

FIG. 8.5, The orthogonal echocardiographic imaging planes and their corresponding anatomical projections.

FIG. 8.6, Graphical summary of the three components used to describe the standard transthoracic echocardiographic (TTE) views in the adult: (1) transducer position or “window,” (2) cardiac imaging plane, and (3) the cardiac region or structure of interest.

FIG. 8.7, Primary cardiac structures and the standard transthoracic echocardiographic views used in their assessment.

FIG. 8.8, Image display convention recommended by the American Society of Echocardiography (1980). The index mark located on the transducer indicates the part of the echocardiographic imaging plane that appears on the right-hand side of the image display.

FIG. 8.9, Panorama of the standard left parasternal long-axis (PLAX) views showing their anatomical orientation (above) , their corresponding cross-sectional anatomy (below right) , and image displays (below left) . The PLAX view (scan plane 1)—typically the first to be obtained in the two-dimensional transthoracic echocardiography examination (see Fig. 8.1 )—is aligned along the long-axis of the left ventricular (LV), aortic root (Ao), and left atrium (LA), and transects both the mitral and aortic valves. The RV inflow view (scan plane 2) transects the right atrium (RA), right ventricle (RV), and the tricuspid valve. The RV outflow view (scan plane 3) transects the RV outflow tract and pulmonary valve. Note that when the transducer is positioned at the left parasternal window, the first cardiac chamber transected is the RV—which appears in the near field of the image display.

FIG. 8.10, Orientation of the parasternal long-axis views of the left ventricular inflow-outflow (PLAX) and the right ventricular (RV) inflow, showing their anatomical orientation (left-hand column) , cross-sectional anatomy (central column), and corresponding image displays (right-hand column) . Note the orientation of the index mark in the anatomical position—directed toward the right shoulder (∼10 o’clock position), compared with the corresponding image display.

FIG. 8.11, Panorama of the standard left parasternal short-axis (PSAX) views showing their anatomical orientation (top panel) , the corresponding cross-sectional anatomy (midpanel), and image displays (below). Note that the PSAX views are oriented orthogonal to the long-axis (LAX) views (see Figs. 8.1 and 8.9 ). The PSAX family of views are acquired following the examination of the parasternal long-axis family of views (see Fig. 8.1 ). The PSAX view at the aortic valve level (AVL, scan plane 1) is typically the first PSAX view to acquire (since it is reliably obtained by rotating the transducer scan plane 90 degrees clockwise, starting from the PLAX view). The PSAX-AVL serves as the reference plane for the scan planes labeled 2–5.

FIG. 8.12, Panorama of the standard apical views with the transducer positioned at the apical (A) window, transecting the left ventricular (LV) apex and the four-chamber (4C) plane. Note their anatomical orientation (top left) , corresponding cross-sectional anatomy viewed from the left lateral supine perspective (bottom panel) , and the corresponding image displays (top right). The A4C view transects the LV apex and all four cardiac chambers (LA, LV, RA, and RV) and septae, with their junction (internal cardiac crux) clearly visible. When the A4C scan plane is superiorly directed, it transects the LV outflow tract and the aortic root (Ao) or “fifth” chamber; hence the term apical five-chamber or A5C view . Optimally acquired apical views should transect the true anatomical apex of the LV. The apical views are acquired following examination of the left parasternal views (see Fig. 8.1 ).

FIG. 8.13, Anatomical orientation and scan plane projections of the apical four-chamber (A4C) view. Two image display options are recommended. Most laboratories use the apex-up projection to display the A4C view, as this is consistent with other imaging protocols such as cardiac computed tomography and cardiac magnetic resonance imaging. The apex-down projection is preferred in pediatric echocardiography.

FIG. 8.14, The apical two-chamber (A2C) view depicting its anatomical orientation (top left), corresponding cross-sectional anatomy viewed from the left lateral supine perspective (bottom panel) , and the corresponding image display options (top right). Note the transducer positioned at the apical window, with the scan plane transecting the left ventricular (LV) apex, the LV chamber, and the left atrium (LA), and the intervening mitral valve (MV). The A2C view is examined following acquisition of the A4C and A5C views (see Fig. 8.1 ).

FIG. 8.15, The apical long-axis view, also called the apical-chamber (A3C) view, depicting its anatomical orientation (top left), corresponding cross-sectional anatomy viewed from the left lateral supine perspective (bottom panel) , and the corresponding image display options (top right). Note the transducer positioned at the apical window, with the scan plane aligned along the long-axis of the left ventricular (LV), aortic root (Ao), and left atrium (LA), and transects both the mitral and aortic valves. Note The A3C view, unlike the parasternal long-axis view, transects the LV apex and apical segments. It is examined following acquisition of the A4C and A5C views (see Fig. 8.1 ).

FIG. 8.16, Subcostal scan planes and corresponding image displays illustrating (1) the subcostal four-chamber view, (2) long-axis view of the inferior vena cava (IVC), and (3) long-axis view of the abdominal aorta (AA). In the adult two-dimensional (2D) transthoracic echocardiographic (TTE) examination, cardiac views obtained from the parasternal and apical windows are generally sufficient to comprehensively assess cardiac structure and function. The subcostal window is therefore used primarily to assess the interatrial and interventricular septae (on the subcostal four-chamber view), and to assess the proximal inferior vena cava, hepatic veins, and the proximal abdominal aorta. In the pediatric examination, subcostal short-axis views of the IVC and AA are typically the first step in the pediatric 2D TTE protocol (bottom panels). They are used to establish situs or position of the heart and organs, as part of the sequential segmental analysis of the cardiac chambers.

FIG. 8.17, Left lateral supine anatomical perspectives of the subcostal scan plane swept along (1) the subcostal four-chamber (SC-4C) plane, (2) the plane swept superiorly through the left ventricular outflow tract, and (3) through the right ventricular outflow tract. If the parasternal and apical windows are obliterated or inaccessible, or as in pediatric echocardiography, the subcostal window can be used to obtain a family of views that approximate short-axis, long-axis, and four-chamber views.

FIG. 8.18, Panoramic perspectives of the suprasternal notch (SSN) scan plane across the long-axis of the aortic arch. In the adult two-dimensional transthoracic echocardiographic examination, the SSN window is used primarily to assess the aortic arch, the distal ascending aorta, and the proximal descending thoracic aorta. The proximal portions of the branches of the aortic arch—the brachiocephalic artery (innominate trunk), the left common carotid artery, and the left subclavian artery—can also be examined using the SSN view. In the pediatric examination, the SSN window is also used to assess the ascending aorta, the main pulmonary artery and branches, as well as the left atrium with its four tributary pulmonary veins ( Figs. 8.19 and 8.20 ).

FIG. 8.19, The suprasternal notch (SSN) window, transducer orientation, and anatomical scan plane used to obtain the SSN-ascending aortic frontal view (upper panels) , with the corresponding scan sector image displays (lower panels).

FIG. 8.20, The suprasternal notch (SSN) window, transducer orientation, and anatomical scan plane used to obtain the SSN aortic arch short-axis view (upper and mid panels) , with the corresponding scan sector image displays (lower panel) . In the pediatric examination, this view is important for visualization of the pair of upper (RUPV, LUPV) and lower (RLPV, LLPV) pulmonary veins as the empty into the left atrium—hence the commonly used term crab view of the left atrium (LA).

FIG. 8.21, The adult two-dimensional transthoracic echocardiography protocol: cross-sectional echocardiographic anatomy based on the American Society of Echocardiography nomenclature and standards.

The 2D TTE examination supplanted the M-Mode examination—a one-dimensional “motion-mode” examination, which remains a useful adjunct to the 2D TTE protocol. The 2D TTE examination is also complemented by additional echocardiography protocols. These include Doppler echocardiography (color flow, spectral, and tissue Doppler) and three-dimensional (3D) echocardiography ( Figs. 8.22–8.24 ). Myocardial segmentation nomenclature and assessment is integral to the 2D TTE examination ( Fig. 8.25 ). 19

FIG. 8.22, Chart summary of the color flow Doppler echocardiography protocol, a major addition to the standard two-dimensional (2D) transthoracic echocardiography examination. Here, mean color-coded velocities are mapped onto the 2D images in real-time. This major addition to the 2D examination facilitates the rapid intuitive assessment of normal and abnormal intracardiac flow patterns. Color-coded, Doppler-derived blood velocities are displayed using conventional color scales, with velocities moving toward the transducer color-coded red, and velocities moving away from the transducer color-coded blue (top panels).

FIG. 8.23, Chart summary of the spectral Doppler echocardiography protocols—pulsed-wave (PW) and continuous-wave (CW) Doppler. Within the cardiovascular system, a wide spectrum of blood flow velocities exists—minimum, maximum, and mean. Spectral Doppler echocardiography is used to quantify this wide spectrum of velocities, hence the term spectral . These modalities are central to the quantitative assessment of intracardiac and transvalvular velocities and pressure gradients, the latter derived by employing the Bernoulli equation. Spectral Doppler-derived blood velocities are graphically displayed by convention, with velocities moving toward the transducer displayed above the baseline, and velocities moving away from the transducer displayed below the baseline.

FIG. 8.24, The three-dimensional (3D) transthoracic echocardiography protocol. The 3D volumes or datasets can be acquired in real time at the standard echocardiographic windows, and then cropped along the orthogonal cardiac imaging planes: the long-axis plane (LAX), short-axis (SAX), and four-chamber (4C) planes.

FIG. 8.25, The two-dimensional transthoracic echocardiographic views showing the superimposed 17-segment model of the left ventricular segments, and their corresponding coronary artery territories. Correlation of regional wall motion abnormalities with their corresponding coronary blood supply is the basis for the echocardiographic assessment of coronary artery disease.

Transducer Positions

The bony chest wall and the air-filled lungs are major obstacles to transmission of the ultrasound beam. Consequently, optimal examination of the adult heart requires placing the ultrasound transducer at specified positions or “windows” on or near the chest wall. Four primary transducer positions or “windows” are recommended. For patients with normal levocardia, the examination begins at (1) the left parasternal window—P, followed by (2) the apical window—A, (3) the subcostal or subxiphoid window—SC, and (4) the suprasternal notch window—SSN ( Fig. 8.2 ).

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