As Low As Reasonably Achievable (ALARA) Principle

The potential benefits and risks of each examination should be considered. The as low as reasonably achievable (ALARA) principle should be observed when adjusting controls that affect the acoustic output and by considering both the transducer dwell time and overall scanning time. Practicing ALARA requires that users do all of the following:

1. Apply correct examination presets if built into the diagnostic ultrasound device. The review of manufacturer default presets for appropriateness is encouraged.

2. Adjust the power to the lowest available setting that provides diagnostic-quality images. If appropriate, reduce power at the end of each examination so the next user will start with the lowest acoustic output setting.

3. Monitor the mechanical index (MI) and thermal index (TI). Know the recommended upper limit of the MI, TI, and related duration limitations for the type of examination being performed.^1,2

4. Apply special care for setting exposures indices and exam duration of sensitive tissues such as the eye, gas-filled tissues (e.g. lung and intestines), and fetal calcified structures (e.g. skull and spine) which have specific guidelines.^2,3

5. Move/lift the transducer when stationary imaging is not necessary to reduce the dwell time on a particular anatomic structure. When possible, avoid fields of view that include the sensitive tissues noted in 4 when not the primary subject of the examination.

6. Minimize the overall scanning time to that needed to obtain the required diagnostic information.

References

1. American Institute of Ultrasound in Medicine. “Recommended maximum scanning times for displayed thermal index (TI) values.” American Institute of Ultrasound in Medicine website. https://www.aium.org/resources/official-statements. Approved July 27, 2026.
2. American Institute of Ultrasound in Medicine. Statement on Biological Effects of Ultrasound in Vivo. Available at: https://www.aium.org/resources/official-statements/view/statement-on-biological-effects-of-ultrasound-in-vivo. Approved Aug 19, 2021.
3. American Institute of Ultrasound in Medicine. Statement and Recommendations for Safety Assurance in Lung Ultrasound. Available at: https://www.aium.org/resources/official-statements/view/statement-and-recommendations-for-safety-assurance-in-lung-ultrasound. Approved July 16, 2023.
4. American Institute of Ultrasound in Medicine. Medical Ultrasound Safety, 4th ed. Laurel, Maryland: American Institute of Ultrasound in Medicine; 2020.