Focused Ultrasound Beam Mapping and Stereotactic Frame Design
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Solution Overview
Problem
Current methods for focused ultrasound (FUS) neuromodulation face challenges in image-guidance accuracy and the need for MRI environments, limiting their routine use due to invasive procedures and poor spatial resolution in non-invasive methods, as well as inadequate signal-to-noise ratio in existing MR coil designs.
Innovation Solution
A method and system for mapping a FUS beam within an MRI environment to create a patient-specific stereotactic frame, allowing for precise delivery of FUS therapy outside the MRI environment with improved accuracy and dosimetry, using MR thermometry and MR-acoustic radiation force imaging for aberration corrections and image guidance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current volume imaging MR coils are used for FUS procedures, then thermometry during thermal ablation is sufficient, but the signal-to-noise ratio is not high enough for functional MRI and parallel imaging capabilities are inadequate
Solution Approach 1:
The patent divides the MR coil system into multiple independent channel coils arranged in an array, where each coil element can be independently optimized and controlled. This segmentation enables parallel imaging capabilities and significantly improves signal-to-noise ratio through coherent signal summation while maintaining manageable complexity through modular design.
Solution Approach 2:
The MR coil array is designed to perform multiple functions: structural imaging, functional MRI, thermometry during thermal ablation, and guidance for focused ultrasound neuromodulation. This multi-functional design eliminates the need for separate specialized coils for each application, reducing overall system complexity while providing superior performance across all functions.
2Ease of operation
If optical tracking or stereotactic methods are used to place the ultrasound transducer relative to the head, then the procedure can be performed outside MRI environment, but the accuracy is limited with errors on the order of 2-3 mm
Solution Approach 1:
The patent performs preliminary MRI-based 3D mapping and aberration measurement of the skull before the actual FUS procedure. This advance characterization of the patient-specific skull geometry and acoustic properties allows for pre-computation of correction factors that are applied during treatment, achieving sub-millimeter accuracy without requiring the transducer to be physically present in the MRI scanner during therapy delivery.
Solution Approach 2:
The system uses MRI-based acoustic radiation force imaging to provide real-time feedback on the actual position and focus of the ultrasound beam within the brain. This feedback loop allows for dynamic adjustment of transducer positioning and beam parameters to maintain sub-millimeter accuracy, overcoming the limitations of initial optical or stereotactic positioning methods.
3Measurement precision
If FUS therapy is delivered inside MRI environment with real-time imaging, then image-guidance accuracy is maximized, but repeated therapy sessions require repeated MRI-guided image guidance which is time-consuming and costly
Solution Approach 1:
The patent performs comprehensive 3D mapping, aberration measurement, and treatment planning using MRI during the initial session. This preliminary characterization creates a patient-specific acoustic model that can be used for subsequent therapy sessions without requiring repeated MRI scanning, significantly reducing time and cost while maintaining accuracy through the use of pre-computed correction factors.
Solution Approach 2:
The system creates a digital copy or model of the patient's skull acoustic properties and brain geometry from the initial MRI scan. This virtual model is used to simulate and plan subsequent FUS treatments, allowing repeated therapy sessions to be performed outside the MRI environment with the same level of precision as if real-time MRI guidance were available, eliminating the need for repeated expensive and time-consuming MRI scans.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables high-accuracy FUS delivery outside the MRI environment with improved imaging metrics and reduced errors, allowing for repeated therapy sessions without repeated MRI-guided image guidance, enhancing spatial precision and safety.
Implementation Method 1
By focusing energy through a transducer, ultrasonic energy can be concentrated to small regions in the skull, including deep brain regions
Implementation Method 2
magnetic resonance imaging (MRI)
Implementation Method 3
the requirement of being within the MR environment is a major barrier for routine use of FUS neuromodulation
Data Source
AI summary
A workflow has been developed that enables initially mapping of a focused ultrasound (FUS) beam using magnetic resonance (MR) thermometry or MR-acoustic radiation force imaging (MR-ARFI) while working within the MRI device. During this procedure, key measurements will be taken including the precise location of the transducer relative to the skull and the transducer parameters (such as amplitudes and phases) required to place the ultrasound focus at the desired focal size and location in the skull. The anatomical measurements will be used to build a patient-specific, device-specific stereotactic frame to hold the transducer in the position relative to the skull and the aberration corrects will be applied. FUS therapy can then be delivered to the patient outside of the MR environment.