New developments in equipment

There has been a rapid improvement in ultrasound scanners suitable for obstetric scanning. Design changes have been made which make the equipment more portable, easier to handle and, by means of automation of functions such as TGC, simpler to use. The image quality has increased significantly in terms of better resolution, improved ability to see textural differences between organs, and in sensitivity. These functional changes have been brought about by major improvements in probe construction technology, and by signal processing techniques largely made possible by the use of digital circuitry. The developments in probe design have included the introduction of dynamic focusing to improve resolution and the incorporation of matching layers to improve sensitivity and reduce reverberation. In linear array probes the elements have been subdivided to reduce radial mode noise and grating lobe artefacts. Convex lenses to focus in the out-of-image plane direction are also used. A range of probes designed for special purposes such as duplex scanning, intracavity scanning and intraoperative scanning, have been developed. Needle guides are also available. Signal processing techniques have improved resolution and sensitivity still further. Digital techniques have made textural contrast variable and selectable after the scan has been completed. The use of microprocessors has made measurement from the image and the subsequent use of look up tables very versatile. The same technology will enable instrument upgrades to be a realistic possibility at a time when major developments are very frequent. High speed digitization is making tissue characterization possible.