Numerical Evaluation of the Influence of Skull Heterogeneity on Transcranial Ultrasonic Focusing
In transcranial penetration, ultrasound undergoes refraction, diffraction, multi-reflection, and mode conversion. These factors lead to phase aberration and waveform distortion, which impede the realization of transcranial ultrasonic imaging and therapy. Ray tracing has been used to correct the phas...
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Frontiers Media S.A.
2020-04-01
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| Series: | Frontiers in Neuroscience |
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| Online Access: | https://www.frontiersin.org/article/10.3389/fnins.2020.00317/full |
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| author | Chen Jiang Dan Li Feng Xu Ying Li Chengcheng Liu Dean Ta Dean Ta Dean Ta |
| author_facet | Chen Jiang Dan Li Feng Xu Ying Li Chengcheng Liu Dean Ta Dean Ta Dean Ta |
| author_sort | Chen Jiang |
| collection | DOAJ |
| description | In transcranial penetration, ultrasound undergoes refraction, diffraction, multi-reflection, and mode conversion. These factors lead to phase aberration and waveform distortion, which impede the realization of transcranial ultrasonic imaging and therapy. Ray tracing has been used to correct the phase aberration and is computationally more efficient than traditional full-wave simulation. However, when ray tracing has been used for transcranial investigation, it has generally been on the premise that the skull medium is homogeneous. To find suitable homogeneity that balances computational speed and accuracy, the present work investigates how the focus deviates after phase-aberration compensation with ray tracing using time-reversal theory. The waveforms are synthetized with ray tracing for phase aberration, by which the properties of the skull bone are simplified for refraction calculation as those of either (i) the cortical bone or (ii) the mean of the entire skull bone, and the focusing accuracy is evaluated for each hypothesis. The propagation of ultrasound for transcranial focusing is simulated with the elastic model using the k-space pseudospectral method. Unlike the fluid model, the elastic model does not omit shear waves in the skull bones, and the influence of that omission is investigated, with the fluid model resulting in a focal deflection of 0.5 mm. The focusing deviations are huge when the properties of the skull bone are idealized with ray tracing as those of the mean of the entire skull bone. The focusing accuracy improves when the properties of the skull bone are idealized as those of the cortical bone. The results reveal minimal deviation (8.6, 3.9, and 3.2% in the three Cartesian coordinates) in the focal region and suggest that transcranial focusing deflections are caused mostly by ultrasonic refraction on the surface of the skull bone. A heterogeneous skull bone causes wave bending but minimal focusing deflection. The proposed simplification of a homogeneous skull bone is more accurate for transcranial ultrasonic path estimation and offers promising applications in transcranial ultrasonic focusing and imaging. |
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| last_indexed | 2024-12-12T23:38:08Z |
| publishDate | 2020-04-01 |
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| series | Frontiers in Neuroscience |
| spelling | doaj.art-7e596ec84845460e86efe8fecdc353e52022-12-22T00:07:19ZengFrontiers Media S.A.Frontiers in Neuroscience1662-453X2020-04-011410.3389/fnins.2020.00317528009Numerical Evaluation of the Influence of Skull Heterogeneity on Transcranial Ultrasonic FocusingChen Jiang0Dan Li1Feng Xu2Ying Li3Chengcheng Liu4Dean Ta5Dean Ta6Dean Ta7Department of Electronic Engineering, Fudan University, Shanghai, ChinaDepartment of Electronic Engineering, Fudan University, Shanghai, ChinaDepartment of Electronic Engineering, Fudan University, Shanghai, ChinaDepartment of Electronic Engineering, Fudan University, Shanghai, ChinaInstitute of Acoustics, Tongji University, Shanghai, ChinaDepartment of Electronic Engineering, Fudan University, Shanghai, ChinaState Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, ChinaKey Laboratory of Medical Imaging Computing and Computer Assisted Intervention (MICCAI) of Shanghai, Shanghai, ChinaIn transcranial penetration, ultrasound undergoes refraction, diffraction, multi-reflection, and mode conversion. These factors lead to phase aberration and waveform distortion, which impede the realization of transcranial ultrasonic imaging and therapy. Ray tracing has been used to correct the phase aberration and is computationally more efficient than traditional full-wave simulation. However, when ray tracing has been used for transcranial investigation, it has generally been on the premise that the skull medium is homogeneous. To find suitable homogeneity that balances computational speed and accuracy, the present work investigates how the focus deviates after phase-aberration compensation with ray tracing using time-reversal theory. The waveforms are synthetized with ray tracing for phase aberration, by which the properties of the skull bone are simplified for refraction calculation as those of either (i) the cortical bone or (ii) the mean of the entire skull bone, and the focusing accuracy is evaluated for each hypothesis. The propagation of ultrasound for transcranial focusing is simulated with the elastic model using the k-space pseudospectral method. Unlike the fluid model, the elastic model does not omit shear waves in the skull bones, and the influence of that omission is investigated, with the fluid model resulting in a focal deflection of 0.5 mm. The focusing deviations are huge when the properties of the skull bone are idealized with ray tracing as those of the mean of the entire skull bone. The focusing accuracy improves when the properties of the skull bone are idealized as those of the cortical bone. The results reveal minimal deviation (8.6, 3.9, and 3.2% in the three Cartesian coordinates) in the focal region and suggest that transcranial focusing deflections are caused mostly by ultrasonic refraction on the surface of the skull bone. A heterogeneous skull bone causes wave bending but minimal focusing deflection. The proposed simplification of a homogeneous skull bone is more accurate for transcranial ultrasonic path estimation and offers promising applications in transcranial ultrasonic focusing and imaging.https://www.frontiersin.org/article/10.3389/fnins.2020.00317/fulltranscranial focusingk-space pseudospectral methodray tracingtime-reversal theoryskull heterogeneity |
| spellingShingle | Chen Jiang Dan Li Feng Xu Ying Li Chengcheng Liu Dean Ta Dean Ta Dean Ta Numerical Evaluation of the Influence of Skull Heterogeneity on Transcranial Ultrasonic Focusing Frontiers in Neuroscience transcranial focusing k-space pseudospectral method ray tracing time-reversal theory skull heterogeneity |
| title | Numerical Evaluation of the Influence of Skull Heterogeneity on Transcranial Ultrasonic Focusing |
| title_full | Numerical Evaluation of the Influence of Skull Heterogeneity on Transcranial Ultrasonic Focusing |
| title_fullStr | Numerical Evaluation of the Influence of Skull Heterogeneity on Transcranial Ultrasonic Focusing |
| title_full_unstemmed | Numerical Evaluation of the Influence of Skull Heterogeneity on Transcranial Ultrasonic Focusing |
| title_short | Numerical Evaluation of the Influence of Skull Heterogeneity on Transcranial Ultrasonic Focusing |
| title_sort | numerical evaluation of the influence of skull heterogeneity on transcranial ultrasonic focusing |
| topic | transcranial focusing k-space pseudospectral method ray tracing time-reversal theory skull heterogeneity |
| url | https://www.frontiersin.org/article/10.3389/fnins.2020.00317/full |
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