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Biomedical Signal and Image Processing
contour images can be revealed from various depths. M-mode is also frequently used
to image movement such as a fetus in the womb, but it is also used to reconstruct
an image by moving the transducer itself to compile the image in summation. Heart
valve diagnosis applies M-mode imaging, and, in other cardiovascular applications,
M-mode is used to analyze deformations in pumping motion of the heart.
16.8 ULTRASOUND IMAGE ARTIFACTS
As with any diagnostic tool, there are limitations to the accuracy of images that are
produced. Many of the artifacts seen in ultrasound images are due to the reflective
properties of the tissues being analyzed. One artifact arises when two reflective surfaces are close to each other and the sound wave bounces between them. In this case,
each time the sound reverberates, some of the sound will transmit through the proximal interface, and an echo will reach the transducer. Consequently, apparent structures
are seen in the image at regular intervals descending down into the tissue although
there may be no structures there at all. This causes a “comet tail” effect in the image.
Another artifact can be seen behind any highly reflective interface that only
transmits a small amount of ultrasound. In such cases, there is not enough sound
energy to reach deeper tissues to produce echoes that are received by the transducer. Consequently, there is tissue beyond the highly reflective surface that the
device cannot register. The resulting areas appear dark on the image and are called
reflective shadows. Echoes reaching the transducer that do not come from the
opposite direction of the incident ultrasound beam cause another artifact, called
displacement. This can occur when a beam of ultrasound is reflected off two or
more reflective surfaces at angles that cause the echo to return to the transducer.
In this case, an apparent structure will appear to be in a place where, perhaps, no
structure exists.
16.9 THREE-DIMENSIONAL ULTRASOUND
IMAGE RECONSTRUCTION
When considering the 2-D ultrasound imaging as a diagnostic tool, some of the
limitations of the 2-D systems can be noticed. In 2-D imaging, only one thin slice
of the patient can be viewed at any time, and the location of this image plane is
controlled by physically manipulating the transducer orientation. Consequently, the
technician or the therapist/surgeon must mentally integrate many 2-D images to
form an impression of the 3-D anatomy and pathology. This process is time consuming and inefficient, but more importantly rather subjective. In addition, due to the
patient’s anatomy or position, it is sometimes impossible to orient the 2-D ultrasound
transducer to obtain the optimal image plane. Three-dimensional imaging will allow
arbitrary orientation of the image viewing plane within the data volume.
Three-dimensional reconstruction of volumes of tissue using ultrasound imaging
is one of the most recent advances in ultrasound technology. In order to form 3-D
images, one must take consecutive scans of the tissue using normal 2-D techniques
and store them in a computer. Then the computer system stacks those images and
Biomedical Signal and Image Processing
contour images can be revealed from various depths. M-mode is also frequently used
to image movement such as a fetus in the womb, but it is also used to reconstruct
an image by moving the transducer itself to compile the image in summation. Heart
valve diagnosis applies M-mode imaging, and, in other cardiovascular applications,
M-mode is used to analyze deformations in pumping motion of the heart.
16.8 ULTRASOUND IMAGE ARTIFACTS
As with any diagnostic tool, there are limitations to the accuracy of images that are
produced. Many of the artifacts seen in ultrasound images are due to the reflective
properties of the tissues being analyzed. One artifact arises when two reflective surfaces are close to each other and the sound wave bounces between them. In this case,
each time the sound reverberates, some of the sound will transmit through the proximal interface, and an echo will reach the transducer. Consequently, apparent structures
are seen in the image at regular intervals descending down into the tissue although
there may be no structures there at all. This causes a “comet tail” effect in the image.
Another artifact can be seen behind any highly reflective interface that only
transmits a small amount of ultrasound. In such cases, there is not enough sound
energy to reach deeper tissues to produce echoes that are received by the transducer. Consequently, there is tissue beyond the highly reflective surface that the
device cannot register. The resulting areas appear dark on the image and are called
reflective shadows. Echoes reaching the transducer that do not come from the
opposite direction of the incident ultrasound beam cause another artifact, called
displacement. This can occur when a beam of ultrasound is reflected off two or
more reflective surfaces at angles that cause the echo to return to the transducer.
In this case, an apparent structure will appear to be in a place where, perhaps, no
structure exists.
16.9 THREE-DIMENSIONAL ULTRASOUND
IMAGE RECONSTRUCTION
When considering the 2-D ultrasound imaging as a diagnostic tool, some of the
limitations of the 2-D systems can be noticed. In 2-D imaging, only one thin slice
of the patient can be viewed at any time, and the location of this image plane is
controlled by physically manipulating the transducer orientation. Consequently, the
technician or the therapist/surgeon must mentally integrate many 2-D images to
form an impression of the 3-D anatomy and pathology. This process is time consuming and inefficient, but more importantly rather subjective. In addition, due to the
patient’s anatomy or position, it is sometimes impossible to orient the 2-D ultrasound
transducer to obtain the optimal image plane. Three-dimensional imaging will allow
arbitrary orientation of the image viewing plane within the data volume.
Three-dimensional reconstruction of volumes of tissue using ultrasound imaging
is one of the most recent advances in ultrasound technology. In order to form 3-D
images, one must take consecutive scans of the tissue using normal 2-D techniques
and store them in a computer. Then the computer system stacks those images and