Introduction: risk and hazard

The words ‘risk’ and ‘hazard’ are emotive terms when used commonly. They are sometimes used to imply that an action should be avoided so as to ensure that there are no risks involved. Strictly, hazard describes the nature of the threat (e.g. burning, electrocution) while the associated risk takes into account the potential consequences of the hazard (e.g. death, scarring) and the probability of occurrence. Ultrasound scanning is potentially hazardous, but the real questions are: ‘Is there any risk for the patient? And if so, what is the correct way to manage this risk?’ The purpose of this chapter is to explain the scientific basis informing the responses to these safety questions, and to describe the ways by which the enviable safety record of diagnostic ultrasound may be maintained.

Whenever an ultrasound scan is carried out, some part of the patient is exposed to an external influence – the ultrasound beam. As it travels through the body, the ultrasound beam interacts with the tissue in ways giving a lasting biological effect, if the exposure is sustained and of sufficient strength. For instance, it is well known that elevated temperature affects normal cell function and that the risk associated with this particular hazard is dependent on the degree of elevation, the duration for which the elevation is maintained and the nature of the exposed tissue.