Data Acquisition

Several parameters must be considered before data acquisition:

There are three modes of data acquisition: (1) narrow-angled acquisition, (2) zoom acquisition, and (3) wide-angled acquisition. The choice of acquisition mode depends on the structure of interest. If the patient has mitral stenosis, a zoom acquisition is best to focus mainly on the mitral valve and reduce the chances of stitch artifacts and a higher frame rate. If left ventricular or right ventricular function were the object of interest, then a wide-angled acquisition would be preferable so that the entire ventricle could be acquired.

Acquisition beats pertain to the number of beats required to build a larger volume. Most systems allow a one-beat acquisition, for instance, of the left ventricle but also have the option of a lower frame rate with higher spatial resolution or a higher frame rate with lower spatial resolution. The most ideal acquisition is a one-beat acquisition with high frame rate and high spatial resolution. However, the physics of ultrasound does not allow this, so there is a tradeoff. The acquisition of valve pathology is best performed by using a one-beat acquisition since it avoids stitch artifacts. However, with a lower frame rate, fine structures may not be optimally visualized.

Image Display and Analysis

There are several methods of image display:

Most systems now acquire data and immediately display images on the ultrasound system without any delay in processing. A volume-rendered image is preferable for visualizing all anatomic structures. Endocardial tracing of a ventricle or chamber results in a wire-frame image, which then can be displayed as a surface-rendered image when a surface is placed over the wire-frame rendition of the structure. A 3D volume can also be displayed as 2D slices to demonstrate ventricular wall motion or measure an orifice such as atrial septal defect (ASD), ventricular septal defect (VSD), or the mitral valve area.

There are many approaches to RT3DE image display. However, after acquiring the data, the cut plane should be displayed so that it can be easily interrupted by the reader or others who are not familiar with RT3DE.

Transducer Technology

Several ultrasound vendors offer products with 3D imaging capabilities incorporated into a 2D imaging probe or an independent 3D imaging probe. With advanced electronics, significant miniaturization has resulted in a fully sampled 3D transesophageal echocardiography probe. Obviously, having one integrated 2D-3D transducer is key, particularly when trying to promote an imaging protocol with 3D imaging. However, in systems with separate 2D and 3D transducers, 3D imaging could be performed after the 2D standard protocol is obtained or even prior to the 2D exam (see Chapter 3). Essentially, the balance of spatial resolution and frame rate is more evident in 3DE compared with 2DE.

Mitral and Aortic Valves

The parasternal long-axis or sagittal view usually is the starting point in most 2DE studies. After obtaining the 2D image, an RT3DE image can be obtained in the same view (Figure 2-1). Typically, adjustments of gain, time-gain compensation, and compression are used to optimize this image. This image can be acquired or used to prepare for zoom imaging of the mitral or aortic valve.

Figure 2-1 Two-dimensional and three-dimensional (3D) parasternal long-axis views, the standard starting point for 3D imaging in the lab. After acquiring this image, the next step is to prepare for zoom imaging of the mitral or aortic valve.

Zoom imaging of the mitral valve is shown in a multiplanar view in Figure 2-2. The RT3DE zoomed view of the mitral valve is displayed from the left atrial and left ventricular views. These views are acquired from one dataset and can be stored for later processing (Figure 2-3). In general, valve structures are shown as if visualized from a surgical perspective and also from a ventricular perspective. In the case of mitral stenosis and mitral valve prolapse, RT3DE imaging provides unique views of this pathology and enables the estimation of the mitral valve area (Figures 2-4 to 2-6).

Figure 2-2 Zoom mitral valve view. From this parasternal long-axis view, a region of interest is placed over the mitral valve and aortic leaflets. The multiplanar display demonstrates a long-axis (A), short-axis view of the mitral valve (B), an orthogonal view of the parasternal long axis (C), and volume-rendered image of the valve from a left atrial perspective (D).

Figure 2-3 From this one real-time three-dimensional echocardiography zoomed dataset of the mitral valve, the valve can be displayed from the left atrial (LA) view in end diastole (upper left) and end systole (upper right) and the left ventricular (LV) view in end diastole (lower left), and end systole (lower right). AMVL, anterior mitral valve leaflet; AV, aortic valve; PMVL, posterior mitral valve leaflet.

Figure 2-4 Mitral stenosis. The pathology in the mitral valve area is more accurately calculated by using three-dimensional echocardiography (bottom right). From the two-dimensional parasternal long axis (left panels), a zoomed volume of the mitral valve is captured (upper right).

Figure 2-5 Two-dimensional (2D) parasternal long-axis view shows mitral valve prolapse. Three-dimensional (3D) echocardiography images from the parasternal long axis (upper right) indicate that the prolapse most likely involves the posterior leaflet. A zoom image on the mitral valve turns the dataset to view the leaflets from the left atrium (lower right). This image shows that the prolapse primarily involves the P2 segment.

Figure 2-6 Left atrial view of mitral valve prolapse (MVP). These zoomed images were acquired from the apical views. On the left is a patient with posterior MVP (arrows) involving most of the posterior segments. On the right is a patient with a flail P3 segment (arrow).

The same imaging mode can be performed on the aortic valve. Figure 2-7 zooms in on the aortic valve from the parasternal window. A multiplanar display of the aortic zoomed dataset demonstrates the parasternal long-axis view (Figure 2-7, upper left), short-axis view (Figure 2-7, upper right), transverse cut (Figure 2-7, lower left), and the RT3DE volume-rendered image (Figure 2-7, lower right), which is cut to display the aortic valve from the aortic side. The aortic valve is displayed from the aortic and left ventricular perspectives (Figure 2-8). Similar views of the aortic and mitral valves may be obtained from an apical window (Figure 2-9).

Figure 2-7 A zoomed aortic valve is shown from the parasternal long-axis view (upper left), short-axis view (upper right), transverse-cut view (lower left), and the real-time three-dimensional echocardiography volume dataset (lower right), which is cut to display the aortic valve from the aortic side.

Figure 2-8 Images of a normal zoomed aortic valve seen in both diastole (left panels) and systole (right panels) as viewed from the aortic side (AO, upper panels) and from the left ventricular side (LV, lower panels).

Figure 2-9 Both the aortic valve (AV) and the mitral valve can be assessed from the apical views. Examples of a zoomed mitral valve (left) and a zoomed aortic valve (right) are shown. AMVL, anterior mitral valve leaflet; LCC, left coronary cusp; LV, left ventricle; LVOT, left ventricular outflow tract; NCC, noncoronary cusp; PMVL, posterior mitral valve leaflet; RCC, right coronary cusp.

Tricuspid Valve

The tricuspid valve can be viewed either from the parasternal long-axis and short-axis views or from the apical view. Capturing the valve from the apical view makes it easier to ensure complete inclusion of the valve. In Figure 2-10, a zoomed image of the tricuspid valve from a parasternal window is shown in a multiplanar display. The tricuspid valve is then displayed from the right atrial and right ventricular views (Figures 2-11 and 2-12; see Videos 2-1 and 2-2).

Figure 2-10 The tricuspid valve can be acquired either from the parasternal long-axis view or from apical views. In the zoomed image of the tricuspid valve, the long axis of the valve (upper left), the orthogonal view of the long axis (upper right), and the short axis of these views (lower left) with a volume-rendered image of the tricuspid valve from a ventricular orientation (lower right) are shown.

Figure 2-11 Normal tricuspid valve. The zoomed tricuspid valve is orientated with the interatrial septum (IAS) posteriorly. The anterior and posterior leaflets are labeled, and the valve is displayed from the right ventricle (upper panels) and the right atrium (lower panels).

Figure 2-12 Tricuspid valve from the parasternal short-axis view. Two-dimensional (2D) view (A) and three-dimensional view (B). Note that with 2D imaging, it is difficult to distinguish the individual leaflets. Part of the septal leaflet is clearly seen attaching to the interventricular septum, but more laterally, part of the anterior and/or posterior leaflet is seen (see Videos 2-1 and 2-2).

Left Ventricle

Acquisition of the left ventricle (LV) could be used to display the volume-rendered images of valves and the anatomy of the LV, and to quantitate left ventricular function. Estimation of left ventricular volumes and function may be performed from multiple ventricular views deriving slice planes from the volume dataset (Figure 2-13). Currently, a wide-angled acquisition can be one beat to six beats. A pyramidal volume dataset, two orthogonal views (four-chamber and two-chamber views), and a short-axis view are shown in Figure 2-14.

Figure 2-13 A triplanar view of the left ventricle acquired in one beat.

Figure 2-14 Left ventricular wide-angled acquisition. This apical left ventricular volume dataset was acquired over four cardiac cycles. The apical four-chamber view (upper left), the apical two-chamber view (upper right), the short-axis or cross-sectional view (lower left), and the rendered full-volume three-dimensional dataset (lower right).

After acquiring the 3D full volume of the LV, this dataset is processed by software to calculate the left ventricular ejection fraction (Figure 2-15). This analysis is demonstrated by two different systems. Note that with both Philips (Andover, MA) (Figure 2-15, A) and TomTec (Munich, Germany) (Figure 2-15, B) analyses of the same dataset, similar ejection fractions of approximately 31.23% (Philips) and 31.95% (TomTec, Inc.) are computed.

Figure 2-15 Left ventricular quantitation. Left ventricular analysis using a semiautomated border detection software (A) and an idealized biplane Simpson’s method of disk volume analysis to derive ejection fraction (EF) and volumes (B). EDV, end-diastolic volume; ESV, end-systolic volume; SDI, systolic dyssynchrony index; SV, systolic volume.

From this apical 3D dataset of the LV (Figure 2-16, A), multiple views can be derived from one full-volume dataset, including a four-chamber view (Figure 2-16, B), two-chamber view (Figure 2-16, C), three-chamber view (Figure 2-16, D), and short-axis view at the level of the mitral valve (lower right, displayed from the left ventricular perspective).

Figure 2-16 Left ventricular real-time three-dimensional (3D) echocardiography volume. From this apical 3D dataset of the left ventricle (A), this volume can be cut and sliced from any direction and the images displayed in a four-chamber view (B), two-chamber view (C), three-chamber view (D), and short-axis view at the level of the mitral valve (E). All these planes are obtained from the one full-volume dataset.

Right Ventricle

The right ventricle (RV) is acquired slightly differently compared with the LV. It is important to ensure that the right ventricular outflow tract (RVOT) is acquired, as seen in Figure 2-17. The right ventricular volume can be displayed from a four-chamber view. Using a cropping plane angled parallel to the tricuspid valve annulus from the apex, the tricuspid valve leaflets and the RVOT could be better visualized from the ventricular perspective (Figures 2-18 and 2-19).

Figure 2-17 Right ventricular real-time three-dimensional echocardiography (RT3DE) volume. This is a full-volume acquisition of the right ventricle. The right ventricular apical view (upper left), the right ventricular outflow tract (upper right), the short axis (lower right), and the rendered RT3DE right ventricular volume (lower right).

Figure 2-18 Real-time three-dimensional echocardiography of the right ventricle. Right ventricular cropping can subsequently be performed. Displayed is the right ventricular apical view (A); using a crop plane, the apex is sliced off (B), further cropping is done (C), and the tilted plane from the lower left panel is turned to the front to show the short axis of the right ventricle (D).

Figure 2-19 Real-time three-dimensional echocardiography of the normal right ventricle. The right ventricle in systole (left) and diastole (right).

Once a right ventricular volume is derived, quantitation of right ventricular function and volumes can be performed either online or offline.

As with any modality, RT3DE can be useful when the data quality is optimal. There is a learning curve in capturing and displaying the RT3DE images. This takes time and practice as well as dedication toward mastery of the technique.

Color Flow Imaging

RT3DE color flow imaging has been one of the more challenging aspects of 3DE. There have been efforts to quantitate the severity of mitral and tricuspid regurgitation; however, it has been more research focused and not used in clinical routine. In a patient with mitral regurgitation caused by perforation, RT3DE color flow demonstrates severe mitral regurgitation from the parasternal view in Figure 2-20. Using RT3DE color flow imaging in a patient with an ASD, the size and location of the ASD can be visualized by using a multiplanar display (Figures 2-21 and 2-22).

Figure 2-20 Right ventricular analysis. EDV, end-diastolic volume; EF, ejection fraction; ESV, end-systolic volume; SV, systolic volume.

Figure 2-21 A patient with a perforated mitral valve leaflet. The pathology can be visualized from the two-dimensional echocardiography image (A and B). The real-time three-dimensional echocardiography images (C and D) show a perforation of the posterior mitral valve leaflet.

Figure 2-22 Patent foramen ovale (PFO) shown in two-dimensional color (top left) and in real-time three-dimensional echocardiography with color (lower left). From this full-volume color dataset, data were analyzed to measure the size of the PFO (right), which was 0.62 cm × 1.14 cm.

Acceptance by and Training of Sonographers and Physicians

There may be two approaches to successfully integrate 3DE into the clinical routine:

Incorporation of Three-Dimensional Echocardiography into Imaging Protocol and Target Population

Integration of 3DE into a routine imaging protocol is essential. Although along with each standard 2DE image a 3DE image could be performed, RT3DE studies should be focused to better demonstrate and interrogate the patient’s pathology. Because of the ease of acquisition and a strong body of evidence demonstrating better accuracy and reliability compared with 2DE, a 3DE left ventricular volume dataset with good image quality should be acquired in all patients. Right ventricular volume acquisition and analysis should depend on the availability of analysis software.

In every study, regardless of the pathology, a dedicated wide-angled acquisition of both the LV and the RV should be routinely acquired; ejection fractions and regional wall motion changes should be calculated and displayed from these volumes. (In our lab, the routine is parasternal long-axis view, parasternal short-axis view, and apical four-chamber view by 3DE. The apical four-chamber view is a full-volume acquisition dedicated to the LV.)

Determination of the target population should be done and included in the lab protocol. It could be applied to all patients with optimal-quality echocardiographic windows to quantitate left ventricular function or focused in patients with a particular pathology, such as congestive heart failure or valvular heart disease, or in those about to receive chemotherapy.

Management of Workflow

It is essential to determine the workflow with regard to 3DE. Once 3D technology has been acquired, display and analysis need to be performed. Depending on the existing 2DE workflow, this could mean a continuation on the ultrasound machine (on-cart) or offline on an image management system that has 3D software. 3D display of pathology or quantitation of ventricular volumes should be recorded as a loop or a still frame for immediate viewing on the image management system (picture archiving and communication system), with subsequent storage of 3D volume as native data for future use.

Although there have been major advances in ultrasound and computer technologies, RT3DE imaging has its limitations. Nonetheless, the developments have enabled more accurate estimation of ventricular function and improved and unique evaluation of valvular pathology. The integration of RT3DE into the clinical routine rests on these facts and the commitment of the leaders in echocardiography laboratories and sonographers.