Effect of skull porosity on ultrasound transmission and wave mode conversion at large incidence angles

Jing, Bowen; Rojas, Stephan Strassle; Lindsey, Brooks D.

doi:10.1002/mp.16318

Cited by 6 publications

(3 citation statements)

References 42 publications

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“…Therefore, during the focusing process, the acoustic waves in the skull are dominated by longitudinal waves. The attenuation of the shear wave in the skull is much higher than that of the compression wave, so the shear wave is usually not used as a focusing wave considering shear waves in the skull model can accurately estimate the energy of the focal point [ 44 ].…”

Section: Modeling Methods and Calculation Resultsmentioning

confidence: 99%

Transcranial Ultrasonic Focusing by a Phased Array Based on Micro-CT Images

Yin,

Yan,

Huang

et al. 2023

Sensors

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In this paper, we utilize micro-computed tomography (micro-CT) to obtain micro-CT images with a resolution of 60 μm and establish a micro-CT model based on the k-wave toolbox, which can visualize the microstructures in trabecular bone, including pores and bone layers. The transcranial ultrasound phased array focusing field characteristics in the micro-CT model are investigated. The ultrasonic waves are multiply scattered in skull and time delays calculations from the transducer to the focusing point are difficult. For this reason, we adopt the pulse compression method and the linear frequency modulation Barker code to compute the time delay and implement phased array focusing in the micro-CT model. It is shown by the simulation results that ultrasonic loss is mainly caused by scattering from the microstructures of the trabecular bone. The ratio of main and side lobes of the cross-correlation calculation is improved by 5.53 dB using the pulse compression method. The focusing quality and the calculation accuracy of time delay are improved. Meanwhile, the beamwidth at the focal point and the sound pressure amplitude decrease with the increase in the signal frequency. Focusing at different depths indicates that the beamwidth broadens with the increase in the focusing depth, and beam deflection focusing maintains good consistency in the focusing effect at a distance of 9 mm from the focal point. This indicates that the phased-array method has good focusing results and focus tunability in deep cranial brain. In addition, the sound pressure at the focal point can be increased by 8.2% through amplitude regulation, thereby enhancing focusing efficiency. The preliminary experiment verification is conducted with an ex vivo skull. It is shown by the experimental results that the phased array focusing method using pulse compression to calculate the time delay can significantly improve the sound field focusing effect and is a very effective transcranial ultrasound focusing method.

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Section: Modeling Methods and Calculation Resultsmentioning

confidence: 99%

Transcranial Ultrasonic Focusing by a Phased Array Based on Micro-CT Images

Yin,

Yan,

Huang

et al. 2023

Sensors

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“…The phase correction results showed varying performance among the four skull models, which may be influenced by multiple factors, including the incident angle, skull density ratio (SDR), and size of the skull. Among these factors, the incident angle and SDR are two significant factors that have been widely studied (Chang et al 2016, Jung et al 2019, Schoen and Arvanitis 2020, Jing et al 2023. It is well known that shear-wave propagation plays an important role when the incident angle large than 20° (White et al 2006).…”

Section: Discussionmentioning

confidence: 99%

A rapid element pressure field simulation method for transcranial phase correction in focused ultrasound therapy

Xu,

Wu,

Shen

2023

Phys. Med. Biol.

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Transcranial focused ultrasound ablation has emerged as a promising technique for treating neurological disorders. The clinical system exclusively employed the ray tracing method to compute phase aberrations induced by the human skull, taking into account computational time constraints. However, this method compromises slightly on accuracy compared to simulation-based methods. This study evaluates a fast simulation method that simulates the time-harmonic pressure field within the region of interest for effective phase correction. Experimental validation was carried out using a 512-element, 670 kHz hemispherical transducer for four ex vivo skulls. The ray tracing method achieved a restoration ratio of 64.81% ± 4.33% of acoustic intensity normalized to hydrophone measurements. In comparison, the rapid simulation method demonstrated improved results with a restoration ratio of 73.10% ± 7.46%, albeit slightly lower than the full-wave simulation which achieved a restoration ratio of 75.87% ± 5.40%. The rapid simulation methods exhibited computational times that were less than five minutes for parallel computation with 8 threads. The incident angle was calculated, and a maximum difference of 6.8 degrees was found when the fixed position of the skull was changed. Meanwhile, the restoration ratio of acoustic intensity was validated to be above 70% for different target positions away from the geometrical focus of the transducer. The favorable balance between time consumption and correction accuracy makes this method valuable for clinical treatment applications.

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“…In addition, the progress made in the noninvasive deep brain ablation surgery based on MRIguided ultrasound focusing (MRgFUS), 10 has brought good news to patients with various brain diseases, such as essential tremor. However, although ultrasound has the advantages of non-invasive, high spatiotemporal resolution, the reflection, scattering, and elastic wave mode conversion of ultrasound by the skull will seriously affect the energy transmission and sound field distribution of transcranial ultrasound, 11 for example, the incidence angle, skull properties (e.g., porosity) can affect mode conversion, thereby reducing the transmission of ultrasound, [12][13][14] making it necessary to open the skull for high-resolution ultrasound imaging, and precise deep brain ablation requires expensive, complex, and huge ultrasound phase array technology. 15 How to overcome the influence of the skull on ultrasound is a major problem in the field of transcranial high-resolution ultrasound imaging and precise modulation.…”

Section: Introductionmentioning

confidence: 99%

Technical note: High‐efficient and wireless transcranial ultrasound excitation based on electromagnetic acoustic transducer

Huang,

Qiao,

Ling

et al. 2023

Medical Physics

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BackgroundThe generation of transcranial ultrasound is usually based on the piezoelectric effect, so it is necessary to attach transducers around the skull. However, the skull will cause serious attenuation and scattering of ultrasound, which makes it particularly difficult for transcranial ultrasound imaging and modulation.PurposeIn transcranial ultrasound imaging, there is significant attenuation and scattering of ultrasound waves by the skull bone. To mitigate this influence and enable precise imaging and high‐efficient transcranial ultrasound for specific patients (such as stroke patients who already require craniotomy as part of their surgical care), this paper proposes to use EMAT to excite metal plates placed inside the skull based on the excellent penetration characteristics of EM waves into the skull, generating ultrasound signals, which can completely avoid the influence of skull on ultrasound transmission.MethodsBased on an efficient wireless transcranial ultrasound experimental platform, we first verified that the skull would not affect the propagation of electromagnetic waves generated by EMAT. In addition, the distribution of the transcranial sound field generated by EMAT was measured.ResultsEMAT can generate 1.0 MHz ultrasound by wireless excitation of a 0.1 mm thick copper plate through an adult skull with a thickness of ∼1 cm, and the frequency and amplitude of the generated ultrasound are not affected by the skull. The results indicated that the electromagnetic waves successfully penetrated the skull, with a recorded strength of approximately 2 mV. We also found that the ultrasound signals generated by the EMAT probe through the skull remained unaffected, measuring around 2 mV. In addition, the measurement of the transcranial sound field distribution (80*50 mm2) generated by EMAT shows that compared with the traditional extracranial ultrasound generation method, the sound field distribution generated by the wireless excitation of the intracranial copper plate based on EAMT is no longer affected by the uneven and irregular skull.ConclusionOur experiments involved validating the penetration capabilities of electromagnetic waves utilizing the EMAT probe through a 7 (5+2) mm thick organic glass plate and a real human skull ranging from 8 to 15 mm in thickness. The efficient and wireless transcranial ultrasound excitation proposed in this paper may be possible for transcranial ultrasound imaging and therapy.

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Effect of skull porosity on ultrasound transmission and wave mode conversion at large incidence angles

Cited by 6 publications

References 42 publications

Transcranial Ultrasonic Focusing by a Phased Array Based on Micro-CT Images

Transcranial Ultrasonic Focusing by a Phased Array Based on Micro-CT Images

A rapid element pressure field simulation method for transcranial phase correction in focused ultrasound therapy

Technical note: High‐efficient and wireless transcranial ultrasound excitation based on electromagnetic acoustic transducer

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