High Intensity Focused Ultrasound Transducer Optimization

Abstract

When planning magnetic resonance (MR) guided high intensity focused ultrasonic (HIFU) therapy, HIFU transducer element parameters are optimized as a function of 3D MR data describing a size, shape, and position of a region of interest (ROI) ( 146 ) and any obstructions ( 144 ) between the HIFU transducer elements and the ROI ( 146 ). Transducer element phases and amplitudes are adjusted to maximize HIFU radiation delivery to the ROI ( 146 ) while minimizing delivery to the obstruction ( 144 ). Additionally or alternatively, transducer elements are selectively deactivated if the obstruction ( 144 ) is positioned between the ROI ( 146 ) and a given transducer element.

What is claimed is: 
     
         1 . Apparatus for magnetic resonance guided high intensity focused ultrasonic ablation including:
 a therapy planning tool that facilitates magnetic resonance (MR) guided high intensity focused ultrasonic (HIFU) ablation planning, including:
 a processor that executes computer-executable instructions for optimizing HIFU transducer element transmission, the instructions comprising:
 evaluating transducer data including transducer element position, geometry, and acoustic parameter information; 
 evaluating 3D MR data including ROI data describing a size, shape, and position of a region of interest (ROI) to be ablated, and obstruction data describing a size, shape, and position of an obstruction between one or more of a plurality of HIFU transducer elements and the ROI; 
 executing an optimizer that determines an optimal waveform that: (i) maximizes HIFU waveform delivery to the ROI while minimizing HIFU waveform delivery to the obstruction and surrounding tissue and, (ii) is determined such that there is no direct shutoff of any of the plurality of HIFU transducer elements during an ablation procedure; and 
 
 a memory that stores the computer-executable instructions, the transducer data, MR data, and a plurality of optimized HIFU parameters; and 
 an HIFU transducer to output ultrasonic energy for an ablation procedure based on the optimal waveform that: (i) maximizes HIFU waveform delivery to the ROI while minimizing HIFU waveform delivery to the obstruction and surrounding tissue and (ii) is determined such that there is no direct shutoff of any of the plurality of HIFU transducer elements during an ablation procedure. 
   
     
     
         2 . The planning tool according to  claim 1 , wherein the optimizer is a phase and amplitude optimizer that optimizes a phase and amplitude of a waveform transmitted from each of the plurality of transducer elements in a HIFU device. 
     
     
         3 . The planning tool according to  claim 2 , the instructions further including:
 performing a Fourier transform on spatial impulse responses from a plurality of probe elements on the ROI and the obstruction;   generating an objective function that describes a ratio of acoustic pressure in the ROI and acoustic pressure at the obstruction; and   generating an initial solution describing a phase and amplitude setting for each transducer element.   
     
     
         4 . The planning tool according to  claim 3 , wherein the phase and amplitude optimizer, when executed by the processor, optimizes phase and amplitude settings for each transducer element as a function of the Fourier-transformed impulse responses, the objective function, and the initial solution. 
     
     
         5 . The planning tool according to  claim 1 , wherein the optimizer is a position optimizer. 
     
     
         6 . The planning tool according to  claim 5 , wherein the position optimizer includes computer-executable instructions that are executed by the processor, the instructions including:
 receiving the ROI data obstruction data, and transducer data including transducer geometry and acoustic parameters;   identifying all transducer elements that are in position to ablate at least a portion of the ROI;   calculating a focal point and thermal deposition of ultrasonic energy deposited in the ROI by each transducer element; and   calculating ROI coverage by the transducer elements.   
     
     
         7 . The planning tool according to  claim 6 , the instructions further including assigning a unique HIFU exposure time and energy to each of a plurality of active transducer elements. 
     
     
         8 . The planning tool according to  claim 1 , wherein the ROI includes liver tissue and the obstruction is a rib. 
     
     
         9 . The planning tool according to  claim 1 , further comprising a magnetic resonance (MR) scanner that generates the ROI data and the obstruction data. 
     
     
         10 . A method of magnetic resonance (MR) guided high intensity focused ultrasonic (HIFU) ablation, including:
 evaluating transducer data including transducer element position, geometry, and acoustic parameter information;   evaluating 3D MR data including ROI data describing a size, shape, and position of a region of interest (ROI) to be ablated, and obstruction data describing a size, shape, and position of an obstruction between one or more of a plurality of HIFU transducer elements and the ROI; and   executing an optimizer that determines an optimal waveform that: (i) maximizes HIFU waveform delivery to the ROI while minimizing HIFU waveform delivery to the obstruction and surrounding tissue and (ii) is determined such that there is no direct shutoff of any of the plurality of HIFU transducer elements during an ablation procedure; and   controlling an HIFU transducer configured to output ultrasonic energy for an ablation procedure based on the optimal waveform that: (i) maximizes HIFU waveform delivery to the ROI while minimizing HIFU waveform delivery to the obstruction and surrounding tissue and (ii) is determined such that there is no direct shutoff of any of the plurality of HIFU transducer elements during an ablation procedure.   
     
     
         11 . The method to  claim 10 , further including:
 optimizing a phase and amplitude of a waveform transmitted from each of the plurality of transducer elements in a HIFU device.   
     
     
         12 . The method according to  claim 11 , further including:
 performing a Fourier transform on spatial impulse responses from a plurality of probe elements on the ROI and the obstruction;   generating an objective function that describes a ratio of acoustic pressure in the ROI and acoustic pressure at the obstruction;   generating an initial solution describing a phase and amplitude setting for each transducer element; and   optimizing phase and amplitude settings for each transducer element as a function of the Fourier-transformed impulse responses, the objective function, and the initial solution.   
     
     
         13 . (canceled) 
     
     
         14 . The method according to  claim 10 , further including:
 receiving the ROI data obstruction data, and transducer data including transducer geometry and acoustic parameters;   identifying all transducer elements that are in position to ablate at least a portion of the ROI;   calculating ROI coverage by the transducer elements;   and   assigning a unique HIFU exposure time and energy to each of a plurality of active transducer elements.   
     
     
         15 . The method according to  claim 10 , wherein the ROI includes liver tissue and the obstruction is a rib. 
     
     
         16 . The method according to  claim 10 , further including:
 generating a patient-specific acoustic path model;   presenting the acoustic path model to a user via a user interface;   receiving user input regarding adjustments to at least one of (i) a position of one or more of the plurality of HIFU transducer elements and (ii) a transmission phase and amplitude of one or more of the plurality of HIFU transducer elements; and   simulating a HIFU sonication of a region of interest (ROI) using the acoustic path model and the user input.   
     
     
         17 . A method of performing an in-situ sonication simulation for an MR-guided high intensity focused ultrasound (HIFU) ablation procedure, including:
 generating a patient-specific acoustic path model;   presenting the acoustic path model to a user via a user interface;   receiving user input regarding adjustments to at least one of (i) a position of one or more HIFU transducer elements and (ii) a transmission phase and amplitude of the one or more HIFU transducer elements; and   simulating a HIFU sonication of a region of interest (ROI) using the acoustic path model and the user input.   
     
     
         18 . The method according to  claim 17 , wherein simulating the HIFU sonication includes:
 segmenting a volume of interest into subvolumes;   extracting and discretizing subvolume boundaries;   positioning a HIFU transducer in a simulation domain;   specifying phases and amplitudes for a plurality of transducer elements in the HIFU transducer;   specifying one or more regions of interest (ROI) in the volume of interest;   selecting a transducer element from the plurality of transducer elements;   launching a discrete computational phonon;   analyzing propagation characteristics of the launched phonon;   storing the launched phonon and path characteristic data in a phonon buffer that stores path characteristic data for a plurality of phonons;   retrieving a new phonon from the phonon buffer;   simulating phonon propagation for the new phonon;   determining whether a ray defining the phonon path intersects a subvolume boundary;   dividing the ray into a transmitted portion and a reflected portion if the ray intersects a subvolume boundary;   determining amplitude and phase information for each of the transmitted and reflected portions of the ray; and   storing the amplitude and phase information for each of the transmitted and reflected portions of the ray in the phonon buffer.   
     
     
         19 . The method according to  claim 17 , wherein simulating the HIFU sonication includes:
 segmenting a volume of interest into subvolumes;   extracting and discretizing subvolume boundaries;   positioning a HIFU transducer in a simulation domain;   specifying phases and amplitudes for a plurality of transducer elements in the HIFU transducer;   specifying one or more regions of interest (ROI) in the volume of interest;   distributing transducer elements into groups;   generating an approximate geometric model for each group of transducer elements;   performing a Fourier transform on a source distribution for each element in a given group;   computing an excited field for each element in the given group;   propagating the excited field to a first boundary plane;   summing the field contributions of each element in the group;   propagating the excited field through a plurality of stacked layers of material;   calculating a transmission coefficient at each boundary for each of a plurality components of the excited field based on a wave vector of each component and material parameters on each side of the boundary;   multiplying the excited field by the transmission coefficient;   propagating the excited field to a next layer of material;   computing an acoustic field in the ROI; and   proceeding to a next group of transducer elements until all groups have been simulated.   
     
     
         20 . The method according to  claim 16 , wherein simulating the HIFU sonication includes:
 estimating an aggregate acoustic field from a subset of transducer elements in a HIFU transducer;   adding estimated acoustic field contributions for additional transducer elements to the aggregate acoustic field estimate one at a time;   after each estimated acoustic field contribution addition, determining whether a user is satisfied with an accuracy of the aggregate acoustic field estimate; and   terminating aggregate acoustic field estimation upon receiving user input indicating that the user is satisfied with the accuracy of the aggregate acoustic field estimate.   
     
     
         21 . The method according to  claim 17 , wherein simulating the HIFU sonication includes:
 segmenting a volume of interest into subvolumes;   extracting and discretizing subvolume boundaries;   positioning a HIFU transducer in a simulation domain;   specifying phases and amplitudes for a plurality of transducer elements in the HIFU transducer;   specifying one or more regions of interest (ROI) in the volume of interest;   selecting a transducer element from the plurality of transducer elements;   launching a discrete computational phonon;   analyzing propagation characteristics of the launched phonon;   simulating phonon propagation for a new phonon;   determining whether a ray defining a path of the new phonon intersects a subvolume boundary;   dividing the ray into a transmitted portion and a reflected portion if the ray intersects a subvolume boundary; and   determining amplitude and phase information for each of the transmitted and reflected portions of the ray.