REAL-TIME ULTRASONIC SCANNER

Typical Number in Hospital: 5

Cost Bands: 6

References: 1

This is an ultrasonic scanner which produces a moving picture at the time of scanning. The expression 'real-time' is an unfortunate use of a computer term which relates to the immediate processing and presentation of information, so that for practical purposes the results are available straight away. Real-time scanners have been available since the mid 1960s, but they did not become popular until about 1976 when a range of new types of scanner was introduced. These include linear array scanners, electronic sector scanners, rocking and rotating transducer types, and moving mirror scanners. Most impact has been made by those with no moving parts. The picture quality with most real- time scanners appears inferior to the classical hand operated B- scanner but it now appears that the overall information gained by the operator is greater using the new types of scanner, partly due to the more positive appreciation of the scanning plane, but mostly due to the extra prompts and landmarks provided by moving structures which enable better identification of organs.

The most common form of real-time scanner is the linear array scanner in which a large hand-held transducer is applied to the skin with a contact area of about 1 cm by 10 cm. The piezo- electric element (crystal) in the transducer is divided into many parallel elements and these are connected in groups so that an active area is commutated along from one end to the other. The picture produced is in the form of a rectangle whose upper short edge corresponds to the face of the transducer. The long edge is the length of the ultrasonic scan line. Apart from the transducer control mechanism, which is wholly electronic, the apparatus need be no more complicated than an A-scanner. Modern types of real-time scanner usually include a frame freeze module by which every point on the picture is stored in a computer memory and can therefore be held on the screen for examination or photography.

Most real-time scanners only perform a 'simple' scan in that each point in the tissue is only interrogated from a single direction.