Recommended maximum exposure times for displayed thermal index (TI) values

Ultrasound has become an indispensable diagnostic tool in many areas of clinical medicine, finding numerous applications, and maintaining an excellent safety record for decades. It is important for its continued use that this safety record is maintained. With advances in ultrasound technology and the proliferation of new clinical applications, the past safety record does not guarantee future safety. For example, artificial intelligence is expanding the potential for ultrasound to be used in novel ways including in the presence of gas bodies, implants, and thermally sensitive tissues like bone and nerve, raising concerns about potential bioeffects. In addition, achieving uniform international guidance is important for reducing confusion and standardizing safe practices. WFUMB* therefore convened a Task Force, one of whose remits was to harmonize existing guidelines for recommended maximum exposure times when specific thermal indices (TIs) are displayed. In carrying out this task guidelines from BMUS⁎⁎, AIUM⁎⁎⁎ and EFSUMB⁎⁎⁎⁎*were compared. In practice the EFSUMB guidelines are identical to those of BMUS.

The use of the term “exposure time” has been adopted and is defined as the "total time that a specified anatomical structure is continuously exposed to the ultrasound beam during an ultrasound examination." In the harmonization of previously recommended maximum exposure times, a number of changes have been implemented. Two categories of application (corresponding to Tables 1 and 2 in the statement) have been defined, chosen by their potential for harm arising from temperature rise. The first (involving applications with potentially higher thermal risk) includes obstetric scanning, gynecological scanning where pregnancy might be possible, and scanning of the neonatal head and spine. Here, the maximum recommended exposure times are unchanged from those contained within existing guidelines. The scanning of premature infants, and of pediatric head and spine, which have not been separately specified in the past, are now included in this category.