OBSTETRIC ULTRASONOGRAPHY - A BIOPHYSICAL CONSIDERATION OF PATIENT SAFETY - THE RULES HAVE CHANGED

We address the issue of health and safety in relation to exposure to d iagnostic ultrasound, with particular emphasis given to obstetrics. In terms of fetal and maternal outcomes, the epidemiologic record of dia gnostic ultrasound is exemplary but is primarily made on the basis of data derived from clinical devices whose outputs were relatively low c ompared with what is now allowable and available. The power outputs of clinical devices have been increasing over the past decade such that the potential for thermal and nonthermal insults is increased. For obs tetric devices that use these higher outputs, the Food and Drug Admini stration now requires the presentation of 2 on-screen indexes, the the rmal index and the mechanical index, in recognition of the 2 major mec hanisms by which ultrasonography is known to affect cells and tissues. Greater responsibility for patient safety is now placed on the diagno stician; for the new indexes to be meaningful the diagnostician must b e cognizant of the health and safety implications. The purpose of this article is to provide some guidance to the obstetrician in interpreti ng the indexes and to review the current status of ultrasonography bio physics in relation to the use of diagnostic ultrasound in obstetrics.