Safety and Bioeffects of Acoustic Radiation Force Impulse (ARFI) in Ultrasound Elastography: A Narrative Review

Acoustic radiation force impulse (ARFI) imaging is an ultrasound elastography technique that enables quantitative assessment of tissue mechanical properties. However, unlike conventional B-mode imaging, ARFI elastography uses longer and higher-intensity push pulses to induce tissue displacement. This feature raises important questions regarding whether the conventional mechanical index (MI) and thermal index (TI) are sufficient to assess the safety of ARFI exposure. In addition, the acoustic field associated with ARFI push pulses may extend beyond the intended focal region, creating the potential for unintended effects to adjacent vulnerable organs, such as the lung or the heart during liver scanning or breast scanning. This narrative review examines the current evidence on the safety of ARFI, with emphasis on direct experimental studies of ARFI bioeffects and their interpretation in the context of international safety guidance from organizations such as the American Institute of Ultrasound in Medicine (AIUM), the British Medical Ultrasound Society (BMUS), and the World Federation for Ultrasound in Medicine and Biology (WFUMB). Available evidence, derived primarily from animal models, suggests that the prolonged pulse duration of ARFI may lower the threshold for certain mechanical bioeffects, including pulmonary capillary hemorrhage and cardiac rhythm disturbances. Concurrent use of ultrasound contrast agents may increase susceptibility to cardiac mechanical bioeffects, whereas no significant increase in ARFI-induced pulmonary hemorrhage was demonstrated in a rabbit lung model under the tested conditions. In vivo rabbit measurements also showed greater temperature rise at the bone surface than in liver tissue during ARFI exposure. These findings indicate that the safety profile of ARFI cannot be inferred solely from criteria developed for conventional diagnostic ultrasound. ARFI-specific factors, including pulse duration, cumulative exposure, tissue vulnerability, off-target exposure, and contrast-agent use, should be considered in safety assessment and clinical practice.