System and method relating to examination of an object
Inventors
Persson, Mikael • Fhager, Andreas • Hashemzadeh, Parham
Assignees
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Publication Number
US-8724864-B2
Publication Date
2014-05-13
Expiration Date
Abstract
The present invention relates to a system and method for non-invasively examination of internal structures of an object by producing dielectric images utilizing reflection and transmission 5 measurements using microwave radiation, characterized by an antenna array surrounding a region of interest for the examination, a microwave transceiver for measuring reflected and transmitted electromagnetic fields, a computational module for receiving detected radiation and for processing data based on the detected radiation, the computational module further being operatively arranged to execute a reconstruction procedure utilized to compute an image of the 10 dielectric profile under detection.
Core Innovation
The invention relates to non-invasively examining internal structures of an object by producing dielectric images utilizing reflection and transmission measurements using microwave radiation. The system comprises an antenna array surrounding a region of interest and a microwave transceiver for measuring reflected and transmitted electromagnetic fields as an electromagnetic pulse, and a computational module receives detected radiation and computes an image of a dielectric profile based on permittivity and conductivity properties of tissue under detection.
The reconstruction procedure executes an iterative computation series performed using at least some frequencies of the electromagnetic pulse. During each iteration, a current gradient is calculated at image points and updated image data from a previous iteration is formed by assigning an a priori dielectric value to image points where the current gradient value is above a threshold value, with the a priori dielectric value used in a next iteration computation.
The iterative computation series ends when a cost functional based on permittivity and conductivity properties of the tissue is minimize, where the cost functional contains a difference between measured image data and updated image data. In additional method aspects, the gradients are calculated from forward and dual Finite-Difference Time-Domain (FDTD) simulations, a driving source is provided as a residual between forwarded FDTD simulations and corresponding measurements, and a line search is performed to determine an optimized threshold level location via evaluation of the cost functional across plural FDTD simulations.
In some approaches, an antenna array provides frequencies optimized for imaging an overall structure, and a processor determines a frequency content of an electromagnetic pulse optimized to image objects of a target size to improve resolution as to the target size objects. Further aspects reconstruct and use constitutive dielectric tensors under constitutive relations, and diagonalize tissue dielectric tensors to obtain principal tissue directions for identifying different tissues.
Claims Coverage
The provided excerpts include three independent claims (system, method, and system variants). Across them, the inventive features focus on iterative reconstruction for dielectric images using reflection and transmission microwave measurements, gradient-driven image point updates using a priori dielectric values above a threshold, and termination using a cost functional comparing measured and updated image data, with additional features for forward and dual FDTD residual computation and FPGA/GPU acceleration; one method variant also includes two-step frequency selection for overall structure versus target-size resolution.
Non-invasive microwave dielectric imaging using reflection and transmission measurements
A system for non-invasively examination of internal structures by producing dielectric images utilizing reflection and transmission measurements using microwave radiation, comprising an antenna array surrounding a region of interest, a microwave transceiver for measuring reflected and transmitted electromagnetic fields as an electromagnetic pulse, and a computational module that computes an image of a dielectric profile based on permittivity and conductivity properties of tissue under detection.
Iterative gradient-based reconstruction with a priori dielectric value thresholding
A reconstruction procedure executed as an iterative computation series using at least some frequencies of the electromagnetic pulse, where during each iteration a current gradient is calculated at image points and reconstructed image data from a previous iteration is updated by assigning an a priori dielectric value to image points where the current gradient value is above a threshold value, using the assigned a priori dielectric value in a next iteration computation.
Cost-functional minimization termination using measured versus updated data
The iterative computation series ends when a cost functional based on permittivity and conductivity properties of the tissue is minimize, where the cost functional contains a difference between measured image data and updated image data.
Forward and dual FDTD simulations with residual driving source and line search
An imaging method that uses a processor to create FDTD simulations of an imaging system, executes dual FDTD simulations with a driving source defined as residual between forwarded FDTD simulations and corresponding measurements, calculates gradients from the forward and the dual FDTD simulations, performs a line search to determine a location of the optimized threshold level in the gradient using plural FDTD simulations and cost-functional evaluation, and updates object starting positions iteratively until convergence.
Two-step frequency optimization for overall structure and target size resolution
A method where a first step of an antenna array provides frequencies optimized for imaging an overall structure and properties of the object, and a second step of a processor determines a frequency content of an electromagnetic pulse optimized to image objects of a target size to thereby improve the resolution of the object structure as to the target size objects.
FPGA and GPU implementation of FDTD code
A system that further includes field programmable gate arrays (FPGA) and a graphics processor unit (GPU) implementing FDTD code thereon.
The independent claims share a common reconstruction concept: iterative dielectric-image computation from reflection and transmission microwave measurements using gradient calculations at image points, assignment of a priori dielectric values above a threshold, and stopping when a cost functional based on tissue permittivity and conductivity and measuring a difference between measured and updated image data is minimized. Additional claim-specific features include dual FDTD simulations with residual driving source and line search for an optimized threshold level, a two-step frequency optimization approach for overall structure versus target size resolution, and FPGA/GPU implementation of FDTD.
Stated Advantages
Not explicitly described in patent.
Documented Applications
Not explicitly described in patent.
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