Biomedical Engineering Reference
In-Depth Information
popular cardiac screening modalities, available at hospitals, medical cen-
ters and cardiologists' offices. Critical information for assessment of car-
diac pathology such as ventricular shape, wall deformation, valve motion,
and blood flow (via Doppler acquisition mode) can be quickly assessed
with this non-invasive, portable and relatively inexpensive screening
modality.
Three-dimensional Echocardiography (3DUS)
: Three-dimensional ultra-
sound was introduced in the late 1980s with offline 3D medical ultrasound
imaging systems. Many review articles have been published over the past
decade, assessing the progress and limitations of 3D ultrasound technol-
ogy for clinical screening [78-81]. These articles reflect the diversity of 3D
systems that were developed for both image acquisition and reconstruc-
tion. The evolution of 3D ultrasound acquisition systems can be divided
into three generations:
- Freehand scanning.
With freehand probes, planar images are ac-
quired at arbitrary spatial positions and orientation with a 2D trans-
ducer. A positioning device, attached to the transducer, tracks its lo-
cation in space and time during the acquisition. A three-dimensional
volume can then be reconstructed by associating each acquired image
with its 3D spatial position and integrating in 3D space. This method
offers a great scanning flexibility and provides high quality images.
The principal limitations of this method are related to the precision of
the positioning device (either mechanical, acoustic or magnetic) and
the experience of the clinician in positioning the device to acquire
sufficient amount of information for an accurate 3D reconstruction.
These issues are most critical when scanning small moving structures
such as valves and myocardium wall defect in cardiac applications.
- Mechanical scanning.
With mechanical scanning, a 2D transducer
is moved at regular intervals along a specified path, ensuring an ac-
curate sampling of the volume to reconstruct with a probe whose
position is controlled in space and time. The three most common
scanning paradigms use linear, fan, and rotational sweep. This tech-
nology provides a more accurate three-dimensional reconstruction of
the anatomy than freehand scanning at the cost of a slower acquisition
