Influence of the skull bone and brain tissue on the sound field in transcranial extracorporeal shock wave therapy: an ex vivo study

Nina Reinhardt; Christoph Schmitz; Stefan Milz; Matías de la Fuente

doi:10.1515/bmt-2022-0332

Abstract

Objectives

Focused ultrasound is mainly known for focal ablation and localized hyperthermia of tissue. During the last decade new treatment options were developed for neurological indications based on blood-brain-barrier opening or neuromodulation. Recently, the transcranial application of shock waves has been a subject of research. However, the mechanisms of action are not yet understood. Hence, it is necessary to know the energy that reaches the brain during the treatment and the focusing characteristics within the tissue.

Methods

The sound field of a therapeutic extracorporeal shock wave transducer was investigated after passing human skull bone (n=5) or skull bone with brain tissue (n=2) in this ex vivo study. The maximum and minimum pressure distribution and the focal pressure curves were measured at different intensity levels and penetration depths, and compared to measurements in water.

Results

Mean peak negative pressures of up to −4.97 MPa were reached behind the brain tissue. The positive peak pressure was attenuated by between 20.85 and 25.38 dB/cm by the skull bone. Additional damping by the brain tissue corresponded to between 0.29 and 0.83 dB/cm. Compared to the measurements in water, the pulse intensity integral in the focal spot was reduced by 84 % by the skull bone and by additional 2 % due to the brain tissue, resulting in a total damping of up to 86 %. The focal position was shifted up to 8 mm, whereas the basic shape of the pressure curves was preserved.

Conclusions

Positive effects may be stimulated by transcranial shock wave therapy but damage cannot be excluded.

Keywords: focused ultrasound; shock wave; sound field; transcranial pressure wave

Corresponding author: Nina Reinhardt, Chair of Medical Engineering, RWTH Aachen University, Aachen, Germany, Phone: +49 241 8023878, E-mail: reinhardt@hia.rwth-aachen.de

Funding source: Richard Wolf GmBH, Knittlingen, Germany

Ethical approval: This manuscript is exempted from obtaining post mortem informed consent because all donors have donated their bodies to the Department of Anatomy of the LMU Munich for teaching and research purposes. According to German law the donation was legally documented in written form and signed by the donors during their lifetime. In such documented cases the ethical approval board at the medical faculty of the LMU has declared that no further ethical approval is necessary.
Informed consent: Not applicable.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Competing interests: Authors state no conflict of interest.
Research funding: This work was supported by Richard Wolf GmbH, Knittlingen, Germany. The funding organization played no role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the report for publication.

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Supplementary Material

This article contains supplementary material (https://doi.org/10.1515/bmt-2022-0332).

Received: 2022-08-25

Accepted: 2023-08-21

Published Online: 2023-09-21

Published in Print: 2024-02-26

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Supplementary Material

Influence of the skull bone and brain tissue on the sound field in transcranial extracorporeal shock wave therapy: an ex vivo study