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Three-dimensional
ultrasonography (3D US) is a technique which allows acquisition of
volumes of data which can be later manipulated and rendered in many
different ways. This technique, also known as volume rendering, allows
for multislice reconstruction in any plane, with cross-sectional
imaging similar to CT scan or MRI. It also allows for surface rendering
of a structure.
By collecting volumes of data in a large sweep, patient exam time
is reduced and there is a less dependance on operator skill, where
post-scan data interpretation is more important.
4D Ultrasound (4D US) is merely 3D US observed in real-time or on video, where time is the fourth dimension.
A 3D US Volume contains a collection or stack of 2D US planes or B-mode images.
This volume of data is in the form of a pyramid where the tip emanates
from the ultrasound transducer. This volume of data is then analyzed
either in real-time (4D US) or later, on a computer using a software
package.
A voxel is the basic unit of a three-dimensional image, just as a pixel is the basic unit of a two-dimensional image. Volume-rendering
is the process of rendering voxel-based images into viewable and usable
2D images. A variety of sophisticated, software-based algorithms exist
for volume-rendering, which will be discussed in the tutorial.
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