Principles of 3D-Echocardiography

Principles of 3D-Echocardiography

Data Acquisition

Three-dimensional echocardiography requires the collection

of a volumetric data set where each image (cut plane) is defined

with respect to its exact position in space [4]. Most systems

currently rely on sequential collection of image planes.

With this technique it is necessary to use ECG and respiratory

triggering or breath hold acquisition to account for motion

artifacts caused by respiration and to permit alignment of the

images in the time domain.

Newer developments use a transthoracic probe technology

with volumetric scanning capabilities, which allows simultaneous

acquisition of an entire 3D-data set. As a result,

data acquisition is less time consuming and less susceptible to

artifacts [5]. 3D-reconstructions have also been applied to

the color Doppler information allowing a three dimensional

representation of jets superimposed on the 3D-grayscale image.

Image acquisition can be performed from both a transthoracic

and a transoesophageal approach (TEE).

Transthoracic 3D-Echo

Three-dimensional transthoracic imaging can be performed

with mechanical steering devices, which are attached to

standard transducers. These devices steer the transducer motion

causing incremental changes in the scan plane either by

rotating, shifting or fanning the probe. In addition, various

locating systems (ie, acoustic or electromagnetic) have been

used effectively. The advantage of this technique is that freely

definable image planes can be chosen allowing for more flexibility.

Others have proposed a rapid (6 seconds) acquisition technique

that collects apical tomograms (within 6 sec) using an

internal continuously rotating transthoracic transducer [6].

Volumetric real-time echocardiography is a recently developed

technique based on the design of an ultrasound

transducer with a matrix array that instantaneously acquires

the image contained in a pyramidal volume. Volumetric realtime

echocardiography is a novel imaging concept, which

holds promise as a “break-through” technology for 3D-echo.

Employing a matrix array echo probe this technique allows

instant (real-time) acquisition of a complete 3-dimensionaldata

set without complex post-processing. Several studies

have already demonstrated the validity of real-time volumetric

echocardiography for the calculation of cardiac volumes

[5]. In addition, real-time volumetric echocardiography allows

the reconstruction of freely definable 2D-image planes

from a single volume set independently of the acquisition

window.

Transoesophageal 3D-Echo

First attempts to acquire a 3-dimensional data set from the

oesophagus were made with a specially designed probe

(echo-CT, lobster tail probe, Tom Tec). This probe was capable

of acquiring parallel data sets by passing a transducer

along the oesophagus [7]. Newer technologies, however, use

multiplane TEE probes that acquire sequential images at different

transducer rotation points (0–180o). 3D-echocardio-simply by mounting the steering device onto the TEE probe.
Data Post-Processing and Representation
Post-processing of the data for sequentially acquired images
is performed off-line using dedicated software. Varying
amounts of user interaction are required to define the region
of interest, view, cut plane, rendering algorithm, filter, magnification
and thresholds. The systems provide a variety of
3D-tools for advanced image processing. Multiplanar, 3Dreconstructions
(volume rendering) as well as wire frame
(surface rendering) display formats can be chosen and measurements
(distance, area, angle, volume) can be performed.
Recent advances in computing capabilities such as parallel
processing have greatly reduced the time necessary for data
manipulation. Three-dimensional reconstruction can now
be achieved within seconds and viewed from different angels
in a dynamic format. It is even possible to “electronically”
dissect the heart to visualize otherwise concealed structures.
Volumetric scanning allows instantaneous (real-time) display
of multiple views (multiplanar) using a split screen. In
addition, prototype systems have demonstrated the feasibility
of near real-time 3D-reconstruction, which permits almost
simultaneous display of 3D-images during the examination.