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As transcranial ultrasound stimulation (TUS) advances as a precise, non-invasive neuromodulatory method, there is a need for consistent reporting standards to enable comparison and reproducibility across studies. To this end, the International Transcranial Ultrasonic Stimulation Safety and Standards Consortium (ITRUSST) formed a subcommittee of experts across several domains to review and suggest standardised reporting parameters for low intensity TUS, resulting in the guide presented here. The scope of the guide is limited to reporting the ultrasound aspects of a study. The guide and supplementary material provide a simple checklist covering the reporting of: (1) the transducer and drive system, (2) the drive system settings, (3) the free field acoustic parameters, (4) the pulse timing parameters, (5) \emph{in situ} estimates of exposure parameters in the brain, and (6) intensity parameters. Detailed explanations for each of the parameters, including discussions on assumptions, measurements, and calculations, are also provided., Comment: 23 pages, 4 figures, 4 tables, stand alone checklist

Transcranial ultrasonic stimulation (TUS) is an emerging technology for non-invasive brain stimulation. In a series of meetings, the International Consortium for Transcranial Ultrasonic Stimulation Safety and Standards (ITRUSST) has established expert consensus on considerations for the biophysical safety of TUS, drawing upon the relevant diagnostic ultrasound literature and regulations. This report reflects a consensus expert opinion and can inform but not replace regulatory guidelines or official international standards. Their establishment by international and national commissions will follow expert consensus. Similarly, this consensus will inform but not replace ethical evaluation, which will consider aspects beyond biophysical safety relevant to burden, risk, and benefit, such as physiological effects and disease-specific interactions. Here, we assume the application of TUS to persons who are not at risk for thermal or mechanical damage, and without ultrasound contrast agents. In this context, we present a concise yet comprehensive set of levels for a nonsignificant risk of TUS application. For mechanical effects, it is safe if the mechanical index (MI) or the mechanical index for transcranial application (MItc) does not exceed 1.9. For thermal effects, it is safe if any of the following three levels are met: a temperature rise less than 2 C, a thermal dose less than 0.25 CEM43, or specific values of the thermal index (TI) for a given exposure time. We review literature relevant to our considerations and discuss limitations and future developments of our approach., Comment: ITRUSST consensus, 15 pages, 1 table, 1 figure

Computational models of acoustic wave propagation are frequently used in transcranial ultrasound therapy, for example, to calculate the intracranial pressure field or to calculate phase delays to correct for skull distortions. To allow intercomparison between the different modeling tools and techniques used by the community, an international working group was convened to formulate a set of numerical benchmarks. Here, these benchmarks are presented, along with intercomparison results. Nine different benchmarks of increasing geometric complexity are defined. These include a single-layer planar bone immersed in water, a multi-layer bone, and a whole skull. Two transducer configurations are considered (a focused bowl and a plane piston), giving a total of 18 permutations of the benchmarks. Eleven different modeling tools are used to compute the benchmark results. The models span a wide range of numerical techniques, including the finite-difference time-domain method, angular-spectrum method, pseudospectral method, boundary-element method, and spectral-element method. Good agreement is found between the models, particularly for the position, size, and magnitude of the acoustic focus within the skull. When comparing results for each model with every other model in a cross comparison, the median values for each benchmark for the difference in focal pressure and position are less than 10\% and 1 mm, respectively. The benchmark definitions, model results, and intercomparison codes are freely available to facilitate further comparisons., Comment: 18 pages, 7 figures