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  • Development of MRI-guided Robotic Hi-intensity Ultrasound Needle/Catheter for Ablation of Brain Metastases

    Final Number:

    Julie G. Pilitsis MD PhD; Gregory S Fischer PhD; E. Clif Burdette PhD

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2014 Annual Meeting

    Introduction: Clinical management of brain metastases poses a significant challenge due to the diversity, clinical presentations, and previous therapies. Our armamentarium of surgical tools consists of biopsy, resection and stereotactic radiosurgery. We describe an approach that is less invasive than craniotomy but provides diagnosis and immediate ablation through a burr hole by using real-time MR imaging and robotic assistance to deliver tumor-geometry-conformal interstitial high-intensity focused ultrasound (iHIFU) to the tumor.

    Methods: We have adapted existing interstitial iHIFU flexible catheter ablation devices and developed delivery enhancements specifically for brain tissue ablation in MRI environment, including smaller diameter and additional insonation directional control. Conformal ablation of multiple angular directions was evaluated in benchtop and ex-vivo studies and results compared to thermal modeling. Temperatures and thermal dose were recorded to examine performance and compared to gross tissue pathology. For accurate delivery under MRI guidance, we adapted our robotic technology to manipulate the ablation probe while inside the scanner bore, incorporate MR image-based tracking of iHIFU probe, and evaluate placement accuracy in phantom studies.

    Results: Electrical to acoustic conversion efficiencies are better than 60% and ablation patterns are in excellent agreement with design parameters. The devices operate at 6.5-7MHz. Tissue ablation was achieved with acoustic power levels of 5-8 watts with treatment times from 5 min to 7 min for a 2cm radial penetration. Based upon analyses of current designs, treatment volumes with effective equivalent spherical diameters from 1cm to 3.5cm can be readily achieved. The robot demonstrated accuracy in phantoms of 0.5mm in placing the probe axis through the target with negligible effect on image quality.

    Conclusions: Our data suggest that a high degree of treatment volume and shape control can be achieved using a small flexible needle iHIFU device robotically localized under MRI guidance. As the robotic assist allows for concurrent MR imaging and thermometry, this device allows for accurate and efficient minimally invasive management of brain tumors.

    Patient Care: It is our goal to influence the neurosurgery community to consider the use of iHIFU needle/catheter devices with advanced stereotactic treatment delivery control capabilities. We believe these devices offer benefits over both surgery and stereotactic radiosurgery and have the potential to improve outcomes for patients with BM.

    Learning Objectives: 1) Understand the potential benefit of utilizing new iHIFU devices placed robotically under MR image guidance, 2) Appreciate that more data are needed on this topic

    References: N/A

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