The Effects of the Structural and Acoustic Parameters of the Skull Model on Transcranial Focused Ultrasound

Abstract

Transcranial focused ultrasound (tFUS) has great potential in brain imaging and therapy. However, the structural and acoustic differences of the skull will cause a large number of technical problems in the application of tFUS, such as low focus energy, focal shift, and defocusing. To have a comprehensive understanding of the skull effect on tFUS, this study investigated the effects of the structural parameters (thickness, radius of curvature, and distance from the transducer) and acoustic parameters (density, acoustic speed, and absorption coefficient) of the skull model on tFUS based on acrylic plates and two simulation methods (self-programming and COMSOL). For structural parameters, our research shows that as the three factors increase the unit distance, the attenuation caused from large to small is the thickness (0.357 dB/mm), the distance to transducer (0.048 dB/mm), and the radius of curvature (0.027 dB/mm). For acoustic parameters, the attenuation caused by density (0.024 dB/30 kg/m3) and acoustic speed (0.021 dB/30 m/s) are basically the same. Additionally, as the absorption coefficient increases, the focus acoustic pressure decays exponentially. The thickness of the structural parameters and the absorption coefficient of the acoustic parameters are the most important factors leading to the attenuation of tFUS. The experimental and simulation trends are highly consistent. This work contributes to the comprehensive and quantitative understanding of how the skull influences tFUS, which further enhances the application of tFUS in neuromodulation research and treatment.

From scalp to cortex, the whole isn’t greater than the sum of its parts: introducing GetTissueThickness (GTT) to assess age and sex differences in tissue thicknesses

“…It is well known that bone yields a particularly strong effect on tFUS, with recent work showing that bone-induced attenuation can be up-to 4.70-7.06 greater than attention caused by the brain or scalp layer (Guo et al 2021). Additionally, it has been shown that bone thickness has the strongest effects on the bone-induced attenuation of tFUS (Zhang et al 2021). In this study, we observed that bone is thinnest in the temporal region (i.e., locations T3 and T4), supporting previous work using the temporal window to place the tFUS transducer to attenuate .…”

“…The volume of grey matter exposed to light emitted by fNIRS is inversely related with SCD, and particularly the thickness of the highly vascularized bone and soft tissue layers strongly affect fNIRS (Rolf and Andrew 2008;Cui et al 2011;Häußinger et al 2011;Takahashi et al 2011;Brigadoi and Cooper 2015). Finally, for tFUS, the thickness of tissues also plays a key role in determining the effects, and the induced sound waves are strongly influenced bone thickness (Guo et al 2021;Zhang et al 2021). Thus, it is critical to understand SCD and the tissues comprising SCD to further elucidate the effects of noninvasive brain stimulation and recording.…”

Low-Intensity Focused Ultrasound Technique in Glioblastoma Multiforme Treatment

“…Perhaps the first factor responsible for this variability is the type of transducer utilized to generate the ultrasonic waves ( 28 ). The second set of parameters is the skull’s impedance to LIFU penetration ( 28 , 48 , 49 ). As the thickness of animal models is not similar to human beings, it is difficult to reproduce the same preclinical effects in the clinic ( 50 ).…”

Biological current source imaging method based on acoustoelectric effect: A systematic review

“…To simulate neural firing, researchers developed a human skull and brain phantom to test and optimize ABI detection of embedded “EEG-like” currents. Because the skull is a strong absorber and disperser of ultrasound and electrical signals (Zhang et al, 2021 ), in earlier studies, the skull cap was removed and ultrasound waves were delivered directly through the surface of the brain phantom (Qin et al, 2016 ). Barragan used a head phantom with a real human skull to demonstrate 4D ABI for mapping time-varying monopoles and dipoles at depths >60 mm with detection thresholds <0.5 mA ( Figure 4 ) (Barragan et al, 2020 ).…”