Toward the next generation in transcranial MR-guided focused ultrasound: Innovations in thermal and acoustic model-based planning and monitoring for improved safety, efficacy and efficiency

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Transcranial MRI-guided focused ultrasound (tcMRgFUS) is a completely non-invasive neuro-interventional technique that shows exceptional promise for treating a number of neurological disorders. The success of focused ultrasound in neurointerventional procedures depends on its ability to deliver a finely focused beam exactly to the desired location and accurately monitor the resulting heating. Although current systems have achieved some success there is strong evidence that patient-specific skull attributes cause the focus to be less than ideal and that changes to the skull during treatment cause further attenuation, broadening, and shifting of the focus. While the Insightec Exablate Neuro tcMRgFUS system has received FDA approval to treat essential tremor, it is not able to 1) fully monitor the insonified field, 2) predict or monitor skull heating, or 3) dynamically optimize beam focusing and power levels needed throughout the procedure. These technical limitations adversely affect the safety, efficacy and efficiency of currently approved tcMRgFUS procedures and limit the number of patients that could otherwise benefit from this revolutionary technology. With prior funding, our research team has introduced important technical advancements for tcMRgFUS, including volumetric real-time MR temperature imaging (MRTI) techniques, T1-based ultrashort echo time (UTE) temperature imaging in cortical bone, rapid ultrasound beam modeling using a hybrid angular spectrum (HAS) method, and radiofrequency (RF) coils specific for tcMRgFUS. Building on this background, our goal in this proposal is to fully develop and disseminate critically needed capabilities that will provide next generation treatment modeling, planning, monitoring, assessment and control. We will accomplish this through three specific aims: 1) Develop robust volumetric MRTI monitoring methods for entire brain and skull including a novel mono flip angle method for T1-based MRTI in the skull and system-specific RF coils to improve MRTI accuracy; 2) Develop patient-specific, dynamic modeling of transcranial ultrasound propagation that adapts to measured temperature changes in the skull, dynamically predicting focusing phases and power needed for accurate treatment completion; and 3) Demonstrate the clinical value of advanced treatment modeling and monitoring tools by incorporating them into a developing tcMRgFUS visualization tool and evaluating the methods in increasingly complex preclinical and clinical environments. These new patient-specific tools combined with the visualization environment will significantly advance tcMRgFUS treatments by providing complete, patient-specific eligibility determination, treatment planning and comprehensive monitoring. This will positively impact beam focusing, localization and tracking, treatment accuracy, and clinical workflow, improving existing clinical indications as well as better enabling forward- looking applications that are still in the translational phase.