Mechanical sector scanners are characterised by the use of an electric motor to move the ultrasonic transducer and when the transducer sweeps over the area of interest the returning echoes are displayed as a series of single line B scans. If the transducer is moved at a frequency several times faster than the rate at which the heart is beating then real time pictures of 2 dimensional sections through the heart are produced. There are two basic ways in which the transducer can be moved (fig. 1). It can be either rotated in one direction 1) or oscillated like a pendulum 2). Our own development was concerned with optimising the design of a hand-held instrument employing an oscillating transducer which pivoted about its front face 3).
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