Influence of bne properties on transcranial acoustic propagation using ray tracing numerical simulations
Résumé
Objective
For transcranial focused ultrasound therapy, acoustic energy is focused through the skull
using a multi-element transducer. Using a ray-tracing numerical simulation method, a
parametric study was conducted to examine the sensitivity of transcranial focalization
quality to variations in the skull's acoustic properties, as well as to the effects of shear
mode conversion and acoustic resonance.
Methods
The parametric study was performed using a ray-tracing method with a model of the
human skull and acoustic source based on the ExAblate Neuro 650kHz (Insightec)
clinical system. The skull properties, including density, acoustic velocity, and degree of
heterogeneity were varied, while focalization quality was quantified using the focal
amplitude and spatial position. The use of a ray-tracing model allowed for the
contributions of shear mode conversion and acoustic resonance in both homogeneous
and multi-layer models of the skull to be examined directly.
Results
The results of this study quantified the sensitivity of the intracranial acoustic field to
variations of skull density, acoustic velocity, and degree of heterogeneity. These findings
illustrate how uncertainties in acoustic properties and increased heterogeneity can have
deleterious effects on transcranial focusing.
Simulations indicate that shear mode conversion had an appreciable effect on
focalization quality in both homogeneous and multi-layer models of the skull, while the
contributions from acoustic resonance remained negligible.
Conclusion
This study quantified the sensitivity of transcranial focalization quality to uncertainties in
acoustic properties of the human skull, and demonstrate the importance of considering
skull heterogeneity and shear mode conversion in ray-tracing models of transcranial
acoustic propagation.
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