Spatio-Spectral Ultrasound Characterization of Reflection and Transmission Through Bone With Temperature Dependence

Area of Science:

• Neurosurgery
• Biomedical Engineering
• Acoustics

Background:

• Transcranial focused ultrasound (tFUS) shows promise for treating neurological disorders, including epilepsy.
• Optimizing tFUS safety and efficacy requires effective access through the temporal window.
• Modern array transducers enable advanced use of the temporal window for targeted brain neuromodulation.

Purpose of the Study:

• To investigate ultrasound reflection and transmission properties through human temporal bone ex vivo.
• To characterize spatio-spectral variability in ultrasound transmission across different temporal window access points.
• To assess the impact of temperature on ultrasound transmission characteristics for tFUS applications.

Main Methods:

• Utilized a dual-piston transducer system operating at 2-7 MHz.
• Employed broadband and orthogonal frequency division multiplexed (OFDM) waveforms for detailed measurements.
• Characterized reflection and transmission coefficients in a temperature-controlled water bath (25°C-43°C).
• Performed hybrid angular spectrum (HAS) simulations based on ex vivo measurements.

Main Results:

• Observed significant spatial, frequency, and temperature-dependent variations in complex reflection and transmission coefficients.
• Transmission phase exhibited greater variability with location and frequency, with less temperature sensitivity.
• Demonstrated dependence of focusing gain on skull properties and speed of sound variations with temperature.

Conclusions:

• Ultrasound transmission through the temporal window is complex and influenced by multiple factors.
• Understanding these variations is critical for developing safe and effective tFUS neuromodulation strategies.
• The findings support the use of advanced techniques for optimizing tFUS delivery via the temporal window.