Ultrasound is now accepted as being of considerable diagnostic value. There is no evidence that diagnostic ultrasound has produced any harm to patients in the four decades that it has been in use. However, the acoustic output of modern equipment is generally much greater than that of the early equipment and, in view of the continuing progress in equipment design and applications, outputs may be expected to continue to be subject to change. Also, investigations into the possibility of subtle or transient effects are still at an early stage. Consequently diagnostic ultrasound can only be considered safe if used prudently.
Thermal hazard exists with some diagnostic ultrasound equipment, if used imprudently.
Temperature elevations in excess of this may cause harm, depending on the time for which they are maintained. With some machines colour Doppler imaging modes may also produce high temperature rises, particularly if a deep focus or a narrow colour box is selected. In view of this, it is recommended that care should be taken to avoid unnecessary exposure of neonatal lung , and to maintain MI as low as possible when this is not possible. However, in view of the difficulty of demonstrating small, localised, regions of damage in vivo , the possibility of this cannot be excluded. The Mechanical Index, if displayed, acts as a guide to the operator.