Impact of acoustic property uncertainty on transcranial ultrasound simulation
Subject-specific simulations of wave propagation are commonly used to plan and report acoustic and thermal exposure during transcranial ultrasound (TUS) interventions. Their accuracy depends on acoustic and thermal tissue property assumptions, including sound speed, density, and attenuation. Reported property measurements vary widely across the literature, precluding consensus point estimates for…
Transcranial ultrasound (TUS) simulations are frequently employed to estimate acoustic and thermal exposure during TUS interventions, relying on assumptions about tissue properties such as sound speed, density, and attenuation. However, the actual measured values for these properties differ considerably in the scientific literature, making it difficult to establish a single point estimate for simulation purposes. The extent to which these property uncertainties influence the estimated exposure has remained unclear.
To address this gap, researchers have compiled bounds for seven acoustic and thermal properties of skull and brain tissue based on published literature. These bounds were then used to evaluate the impact of individual property variations on simulated intensity and temperature rise using two distinct simulation platforms: PRESTUS/k-Wave and BabelBrain.
The findings reveal that variations in skull attenuation and absorption have the most significant impact on the estimated outcomes. For instance, peak intensity in the brain can fluctuate by roughly threefold solely due to changes in skull attenuation. Similarly, absorption plays a crucial role in determining temperature rise within the skull.
The direction of each parameter's effect remained consistent across both simulation platforms, with one exception, and across different skull thicknesses. This consistency allowed researchers to combine the bounds into setups that bracket transmission and temperature rise. When comparing these extreme scenarios to the default property sets used in three popular simulation toolboxes (k-Plan, BabelBrain, and PRESTUS), it was observed that the default values resulted in similar brain intensity but divergent skull heating.
The primary reason behind this discrepancy was the differing assumptions made by each toolbox regarding skull absorption and heat capacity.
The results of this study highlight that uncertainties in skull acoustic properties represent a significant source of variability in TUS exposure estimates. To ensure safe, effective, and reproducible planning for TUS interventions, the authors emphasize the need for refined measurements of these acoustic properties and explicit reporting of exposure uncertainty. This approach will help minimize the variability introduced by property uncertainties and promote better planning and execution of TUS procedures.
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