Optimizing sonication protocols for transthoracic focused ultrasound surgery

J. Gao, A. Volovick, R. Cao, G. Nabi, S. Cochran, A. Melzer, Z. Huang

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    1 Citation (Scopus)

    Abstract

    During transthoracic focused ultrasound surgery (TFUS), the intervening ribs absorb and reflect the majority of the ultrasound energy excited by an acoustic source, resulting in pain, bone injuries and insufficient energy delivered to the target organs of liver, kidney, and pancreas. Localized hot spots may also exist at the interfaces between the ribs and soft tissue and in the highly absorptive regions such as the skin and connective tissue. The aims of this study were to clarify the effects of focal beam distortion and frequency-dependent rib heating in TFUS and to propose possible techniques to reduce the side-effects of rib heating and increase ultrasound efficacy. Frequency-dependent heating at the target and the ribs were estimated using finite element analysis (PZFlex, Weidlinger Associates Inc, USA) along with experimental verification on a range of different phantoms. The ratio of ultrasonic power density at the target and the ribs, the time-varying spatial distribution of temperature, and the ablated focus of each sonication were taken as key indicators to determine the optimal operating frequency. Comparison with a patient specific model was also made. TFUS seems to be useful to treat tumours that are small and near the surface of the abdominal organs. For targets deep inside these organs, severe attenuation of energy occurs, suggesting that purely ultrasound thermal ablation with advanced heating patterns will have limited effects in improving the treatment efficacy. Results demonstrate that the optimal ultrasound frequency is around 0.8 MHz for the configurations considered, but this may shift to higher frequencies with changes in the axial and lateral positions of the tumours relative to the ribs. To date, we have elucidated the most important effects and correlated these with idealised anatomical geometry. The changes in frequency and other techniques such as selection of excited element patterns in FUS arrays had some effect. However, more advanced techniques need to be explored for further enhanced localised heating in the TFUS study, if this is to prove fully effective.

    Original languageEnglish
    Title of host publication12th International Symposium on Therapeutic Ultrasound
    EditorsStephen Meairs
    Place of PublicationMelville
    PublisherAmerican Institute of Physics
    Pages146-151
    Number of pages6
    ISBN (Print)9780735411203
    DOIs
    Publication statusPublished - 2012
    Event12th International Society for Therapeutic Ultrasound Symposium - Heidelberg Convention Center, Heidelberg, Germany
    Duration: 10 Jun 201213 Jun 2012
    http://www.istu.org/events/ann2012/ann2012.aspx

    Publication series

    NameAIP conference proceedings
    PublisherAmerican Institute of Physics
    Volume1503
    ISSN (Print)0094-243X

    Conference

    Conference12th International Society for Therapeutic Ultrasound Symposium
    Abbreviated titleISTU 2012
    CountryGermany
    CityHeidelberg
    Period10/06/1213/06/12
    Internet address

    Keywords

    • rib cage
    • Transthroracic focused ultrasound surgery
    • TUMORS
    • FEASIBILITY
    • RIB CAGE
    • HIFU
    • LIVER
    • ARRAY
    • ABLATION
    • sonication protocol

    Cite this

    Gao, J., Volovick, A., Cao, R., Nabi, G., Cochran, S., Melzer, A., & Huang, Z. (2012). Optimizing sonication protocols for transthoracic focused ultrasound surgery. In S. Meairs (Ed.), 12th International Symposium on Therapeutic Ultrasound (pp. 146-151). (AIP conference proceedings; Vol. 1503). Melville: American Institute of Physics. https://doi.org/10.1063/1.4769933
    Gao, J. ; Volovick, A. ; Cao, R. ; Nabi, G. ; Cochran, S. ; Melzer, A. ; Huang, Z. / Optimizing sonication protocols for transthoracic focused ultrasound surgery. 12th International Symposium on Therapeutic Ultrasound. editor / Stephen Meairs. Melville : American Institute of Physics, 2012. pp. 146-151 (AIP conference proceedings).
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    abstract = "During transthoracic focused ultrasound surgery (TFUS), the intervening ribs absorb and reflect the majority of the ultrasound energy excited by an acoustic source, resulting in pain, bone injuries and insufficient energy delivered to the target organs of liver, kidney, and pancreas. Localized hot spots may also exist at the interfaces between the ribs and soft tissue and in the highly absorptive regions such as the skin and connective tissue. The aims of this study were to clarify the effects of focal beam distortion and frequency-dependent rib heating in TFUS and to propose possible techniques to reduce the side-effects of rib heating and increase ultrasound efficacy. Frequency-dependent heating at the target and the ribs were estimated using finite element analysis (PZFlex, Weidlinger Associates Inc, USA) along with experimental verification on a range of different phantoms. The ratio of ultrasonic power density at the target and the ribs, the time-varying spatial distribution of temperature, and the ablated focus of each sonication were taken as key indicators to determine the optimal operating frequency. Comparison with a patient specific model was also made. TFUS seems to be useful to treat tumours that are small and near the surface of the abdominal organs. For targets deep inside these organs, severe attenuation of energy occurs, suggesting that purely ultrasound thermal ablation with advanced heating patterns will have limited effects in improving the treatment efficacy. Results demonstrate that the optimal ultrasound frequency is around 0.8 MHz for the configurations considered, but this may shift to higher frequencies with changes in the axial and lateral positions of the tumours relative to the ribs. To date, we have elucidated the most important effects and correlated these with idealised anatomical geometry. The changes in frequency and other techniques such as selection of excited element patterns in FUS arrays had some effect. However, more advanced techniques need to be explored for further enhanced localised heating in the TFUS study, if this is to prove fully effective.",
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    Gao, J, Volovick, A, Cao, R, Nabi, G, Cochran, S, Melzer, A & Huang, Z 2012, Optimizing sonication protocols for transthoracic focused ultrasound surgery. in S Meairs (ed.), 12th International Symposium on Therapeutic Ultrasound. AIP conference proceedings, vol. 1503, American Institute of Physics, Melville, pp. 146-151, 12th International Society for Therapeutic Ultrasound Symposium, Heidelberg, Germany, 10/06/12. https://doi.org/10.1063/1.4769933

    Optimizing sonication protocols for transthoracic focused ultrasound surgery. / Gao, J.; Volovick, A.; Cao, R.; Nabi, G.; Cochran, S.; Melzer, A.; Huang, Z.

    12th International Symposium on Therapeutic Ultrasound. ed. / Stephen Meairs. Melville : American Institute of Physics, 2012. p. 146-151 (AIP conference proceedings; Vol. 1503).

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

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    T1 - Optimizing sonication protocols for transthoracic focused ultrasound surgery

    AU - Gao, J.

    AU - Volovick, A.

    AU - Cao, R.

    AU - Nabi, G.

    AU - Cochran, S.

    AU - Melzer, A.

    AU - Huang, Z.

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    AB - During transthoracic focused ultrasound surgery (TFUS), the intervening ribs absorb and reflect the majority of the ultrasound energy excited by an acoustic source, resulting in pain, bone injuries and insufficient energy delivered to the target organs of liver, kidney, and pancreas. Localized hot spots may also exist at the interfaces between the ribs and soft tissue and in the highly absorptive regions such as the skin and connective tissue. The aims of this study were to clarify the effects of focal beam distortion and frequency-dependent rib heating in TFUS and to propose possible techniques to reduce the side-effects of rib heating and increase ultrasound efficacy. Frequency-dependent heating at the target and the ribs were estimated using finite element analysis (PZFlex, Weidlinger Associates Inc, USA) along with experimental verification on a range of different phantoms. The ratio of ultrasonic power density at the target and the ribs, the time-varying spatial distribution of temperature, and the ablated focus of each sonication were taken as key indicators to determine the optimal operating frequency. Comparison with a patient specific model was also made. TFUS seems to be useful to treat tumours that are small and near the surface of the abdominal organs. For targets deep inside these organs, severe attenuation of energy occurs, suggesting that purely ultrasound thermal ablation with advanced heating patterns will have limited effects in improving the treatment efficacy. Results demonstrate that the optimal ultrasound frequency is around 0.8 MHz for the configurations considered, but this may shift to higher frequencies with changes in the axial and lateral positions of the tumours relative to the ribs. To date, we have elucidated the most important effects and correlated these with idealised anatomical geometry. The changes in frequency and other techniques such as selection of excited element patterns in FUS arrays had some effect. However, more advanced techniques need to be explored for further enhanced localised heating in the TFUS study, if this is to prove fully effective.

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    KW - Transthroracic focused ultrasound surgery

    KW - TUMORS

    KW - FEASIBILITY

    KW - RIB CAGE

    KW - HIFU

    KW - LIVER

    KW - ARRAY

    KW - ABLATION

    KW - sonication protocol

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    M3 - Conference contribution

    SN - 9780735411203

    T3 - AIP conference proceedings

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    BT - 12th International Symposium on Therapeutic Ultrasound

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    Gao J, Volovick A, Cao R, Nabi G, Cochran S, Melzer A et al. Optimizing sonication protocols for transthoracic focused ultrasound surgery. In Meairs S, editor, 12th International Symposium on Therapeutic Ultrasound. Melville: American Institute of Physics. 2012. p. 146-151. (AIP conference proceedings). https://doi.org/10.1063/1.4769933