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).