Ultrasound: Adverse reactions

Adverse effects from ultrasound include:

localized temperature rise in tissue,

cavitation (growth of gas bubbles),

steady radiation force exerted on tissue structures (which may result in movement),

streaming agitation in liquids,

shear stress of objects in the streaming liquid and the

oscillatory force of the sound field on all structures

but these are only observed at acoustic intensities well above the 'safe' limit.

There is no room for complacency, though. As with all scanning procedures exposure times and intensities should be kept as low as possible. Patient exposure should be minimized and logged carefully, especially in the case of pregnant women.

Output from machines can vary considerably and manufacturer's specifications should be verified. The machine should be regularly checked to ensure that predicted manufacturer's output is 'true'.
 

It has been well over half a century since ultrasound was first used on pregnant women. Unlike X-rays, ionizing irradiation is not present and embryotoxic effects associated with such irradiation should not be relevant.

Safety Testing

Only the use of high intensity ultrasound is associated with the effects of "cavitation" and
"heating" which can be present with prolonged insonation in laboratory situations.

Harmful effects in cells of experimental animals or humans however have not been demonstrated in the large amount of studies that have so far appeared in the medical literature purporting to the use of diagnostic ultrasound in the clinical setting. Findings in one study reporting lower birth-weights in babies exposed to prenatal ultrasound have not been reproducible.

Nevertheless it is general consensus that ultrasound scans should best be performed when there is an indication to do so.