Biosafety of low-intensity pulsed transcranial focused ultrasound brain stimulation: a human skull study

Among a variety of existing modalities for noninvasive brain stimulation (NIBS), low-intensity pulsed transcranial focused ultrasound (tFUS) is a promising technique to precisely stimulate deep brain structures due to its high spatial specificity and superior penetration depth. While tFUS is gaining momentum as an emerging NIBS technique, an advisable biosafety-associated combination of sonication parameters including duty cycle and power input remains to be explored. In this study, biosafety of low-intensity pulsed tFUS using various sonication parameters was evaluated by measuring acoustic intensities and temperature variations across a piece of real human skull. The results showed that ISPTA above 480 mW/cm^2 is likely to induce an excessive temperature rise for a sonication duration of 160 seconds. Also, the skull base effect and ultrasound transducer self-heating effect should be noted during the sonication. Based on the findings in this study, an initial biosafety guide was discussed for the future investigation of ultrasound-mediated NIBS.