Ultra-broadband Transcranial Ultrasound by Acoustic Phase-only Hologram with a Tungsten Metalens

Abstract

With the advancements in modern imaging techniques, such as MRI, CT imaging, and nuclear medicine, powerful functional imaging modalities have emerged. The human skull, as a barrier for energy transmission, poses significant challenges for the clinical application of transcranial ultrasound. High-intensity focused ultrasound (HIFU), as an effective tool for modern biomedical tumor imaging and treatment, has benefited from the use of structured focusing transducers, which generate axial pressure waves and induce localized thermal effects within tissues, enabling precise destruction of tumor tissue while minimizing damage to surrounding normal tissue. To date, the preclinical optimization design path for transcranial ultrasound focusing lenses remains uncertain due to the complex interaction between the structured piezoelectric transducer's near-field coherence and the human skull. For achieving arbitrary wavefront shaping and biomedical transcranial monitoring, holographic techniques are fundamental to applications with high-density data storage and spatial control of intricate acoustic fields. The basic of phase-only acoustic hologram is spatial storage the phase profile of the desired wavefront from real human skull in a manner that allows for wavefront reconstruction by near-field interaction when hologram metalens is illuminated with a suitable coherent source. We propose that by introducing the micro-tungsten-based metalens via acoustic hologram, the arbitrary shaped scattering effect from human skull could be eliminated. The static non-resonance-based design is key to achieving ultra-broadband material properties, which differs from the resonant-based effective medium theory such as dynamic homogenization scheme for acoustic metamaterials. The experimental results show that newly-developed tungsten metalens via acoustic hologram performs well over frequency from 100 kHz to 500 kHz and near-field received sound pressure level (SPL) is improved about 9 dB without human skull when introducing the real human skull. Applications show that our designed micro-tungsten-based metalens performs well than traditional curved focus lens.