Guidelines for the Safe Use of Diagnostic Ultrasound - Scope and Purpose

1. Scope and Purpose

Diagnostic ultrasound is a valuable modality and is not contraindi-cated where medical benefit is expected. Furthermore, there are no confirmed biological effects on patients caused by exposures from present diagnostic ultrasound instruments. However, the possibility exists that such biological effects may be identified in the future. Therefore, the intent of these guidelines is to help equipment manufacturers and operators ensure both the prudent use of diagnostic ultrasound and the continued excellence of its safety record. To this end, the guidance in this document should help equipment operators to identify exposures that are potentially hazardous and to ensure that the exposures they use are justified.

Manufacturers are also reminded to ensure that Health Canada has licensed any of their diagnostic ultrasound devices that are offered for sale or lease in Canada. Licensing requirements can be obtained from the Licensing Division of Health Canada's Medical Devices Bureau.

This update replaces all parts of Safety Code 23 "Guidelines for the Safe Use of Ultrasound -Part 1: Medical and Paramedical Applications (1989)"pertaining to the safe use of diagnostic ultrasound devices. Several developments in the past decade have necessitated this update. First, methods have been developed for estimating the maximum temperature elevation in exposed tissues during clinical examinations (see Sections 3.2 and 4.1). These estimates indicated that during some Doppler blood flow examinations, temperature elevations could exceed 1 °C. Computed estimates of maximum temperature elevations have been as high as 6-10 °C. Also, biological effects studies have demonstrated capillary hemorrhaging in vivo in the lungs of several mammalian species (though not humans), as a result of pulsed ultrasound exposures in the range of those available from diagnostic devices, including B-mode imaging. This effect was purely mechanical, having been found in the absence of ultrasonic heating (see Sections 3.3 and 4.2).

In addition to these discoveries, regulatory changes in the U.S.A. have increased the potential for relatively high acoustic outputs to be available (U.S Food and Drug Administration 1997). Also, a voluntary standard was developed for diagnostic ultrasound devices to provide the equipment operator with a real-time display of Thermal and Mechanical Indices. These exposure indices are related to the potential for heating or mechanical effects, respectively, during the ultrasound examination (AIUM/NEMA 1998a, Abbott 1999).

The information presented in this update summarizes these developments and forms the basis for new recommendations for users and manufacturers. The update is also heavily based on U.S. and other national and international recommendations and guidelines for the safe use of diagnostic ultrasound (Barnett, et al., 2000, AIUM 2000).

The required new terminology is in bold in the text and is explained in the Glossary of Terms, Section 6. In this glossary, the terms used in the guidelines are explained primarily for equipment operators and other interested parties. This is done in as plain language as possible without distorting the meaning of the term. Of particular note is the extension of the ALARA principle to ultrasound exposures.

Manufacturers endeavouring to implement this document's recommendations for device performance will need to consult the referenced standards and the U.S. Food and Drug Administration 510(k) guidance document (1997).