Standing-wave suppression for transcranial ultrasound by random modulation

Area of Science:

• Acoustic physics
• Biomedical engineering
• Neuromodulation

Background:

• Low-frequency transcranial ultrasound (<1 MHz) shows promise for brain therapies (stroke, tumor ablation, blood-brain barrier opening).
• Undesired standing waves and cavitation are significant challenges at lower ultrasound frequencies.
• Effective mitigation of standing waves is crucial for safe and precise ultrasound brain applications.

Purpose of the Study:

• To investigate a novel approach for suppressing standing waves during continuous-wave (CW) transcranial ultrasound application.
• To evaluate the efficacy of frequency randomization in mitigating standing waves compared to single-frequency and swept-frequency methods.
• To assess the potential for improved safety in ultrasound-based brain therapies.

Main Methods:

• Studied a frequency randomization technique for continuous-wave (CW) transcranial ultrasound.
• Evaluated the approach using ex-vivo human skull and a plastic-walled chamber under idealized conditions.
• Compared acoustic field scans against single-frequency CW excitation and swept-frequency inputs.

Main Results:

• Swept-frequency input suppressed standing waves 3.4x in a plastic chamber and 1.6x in a human skull compared to single-frequency CW.
• Random frequency modulation reduced standing waves 5.6x in the plastic chamber and 2x in the human skull.
• Frequency randomization demonstrated superior standing wave suppression compared to swept-frequency methods.

Conclusions:

• Frequency randomization is an effective strategy for suppressing standing waves in low-frequency transcranial ultrasound.
• This approach offers a potential pathway to enhance the safety and efficacy of ultrasound brain therapies.
• The findings may have broader implications for applications susceptible to standing wave generation.