ULTRASONIC SCANNER

Typical Number in Hospital: 5

Cost Bands: 6

References: 1

Ultrasonic scanners produce echo pictures from within the body. They may be divided into A-scanners, B-scanners (including real- time), M-mode, and doppler instruments. First introduced in the early 1960s they have found widespread use in obstetrics, and for producing images of the liver, kidney, heart, arteries, etc. Development of these devices continues rapidly.

1. A-scanner. A hand-held transducer, applied to the skin, produces a single line on a CRT screen showing the depth of reflecting surfaces. It is used for showing the position of the central structures in the head. It is also used in conjunction with some B-scanners for measurement and setting up.

2. B-scanner. This produces a two-dimensional section scan on a CRT screen which represents a plane of tissue in line with the transducer. The transducer is made to perform a scanning action, to build up the picture from returning echoes. The scanning action may be linear, sector, or compound, and may be produced by hand movement of the transducer, or by motorized rotation or rocking, or produced electronically by switching or phasing pulses to the transducer. Most B-scanners produce moving pictures.

3. M-Mode scanner. A line of dots, representing reflecting surfaces under the transducer, is swept slowly across a long-persistence CRT display so that moving structures can be identified. Such scanners have been used extensively in cardiology for the study of heart valve defects.

4. Doppler Scanner. Information about the movement of blood derived from ultrasonic doppler signals can be assembled into a picture showing only moving parts of the tissue being scanned. Such devices can provide information about vascular disease.

There are other ways in which ultrasonic scanners can be classified, and there are combinations of the above types. Examples are Duplex scanners, which are combinations of B-mode and doppler scanners, C-scanners, transmission scanners, and plan position scanners.