Biomedical Engineering Reference
In-Depth Information
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FIGURE 16.3 Amplitude reflection factor for tissues normalized to the impedance of blood and plotted on a
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flow in the heart through Doppler-shifted motion, and I. Edler and C. H. Hertz in Sweden
studied the motion of the heart and started echocardiography, the use of ultrasound to
study the properties and dynamics of the heart.
Investigators around the world continued to make progress with the development of
ultrasound imaging. Even though internal organs and the dynamics of heart motion could
be detected with ultrasound, ultrasound remained a laboratory curiosity. Until the early
1960s, mothers and fetuses were imaged by x-rays. A 1956 report by Alice Stewart, an
English epidemiologist, linked deaths from cancer in children to their mothers' exposure
to x-rays during pregnancy. This tragic finding gave ultrasound imaging its first commer-
cial opportunity to provide a safe alternative for fetal imaging.
During the early 1960s, several companies developed ultrasound imaging systems suit-
able for imaging fetuses and other internal organs. R. Soldner of Siemens designed the first
real-time mechanical ultrasound imaging scanner in 1965 in Germany. Drs. I. McDonald
and T. G. Brown developed the first commercially successful diagnostic ultrasound imag-
ing system, the Diasonograph, in 1968.
These investigators eventually preferred a pulse-echo method of ultrasound imaging with
equipment similar to that shown in Figure 16.4. The image is made up of a sequential arrange-
ment of echo ranging lines, where each line would correspond to each pulse in a sequence,
such as that depicted in Figure 16.1. The diagram shows an oval-shaped object with a sound
beam piercing it. The sound is transmitted, and received echoes corresponding to the front
and back boundaries of the oval at that beam location are then displayed as white dots on a
vertical echo line with time increasing in the downward direction on a monitor. Next, the
transducer is moved to another location, and the process is repeated until all the lines have
been sent. The resulting series of lines, geometrically arranged on the display to correspond
to the actual positions of the transducer, result in an ultrasound image of the object. These
early images were viewed either on long persistence cathode ray tubes or captured with
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