Patent ID: 6636584
Filing Date: 2003-10-21
Classification: A61B,G01H,G01N,G01S,G01V,G06T,Y10S

Abstract:
A method for producing an image of an object in a region from wavefield energy that has been transmitted into and scattered by the object, said image comprising a map of selected physical characteristics at selected points within the region, said image being stored in a computer memory, and said method comprising the steps of:(a) transducing an electric signal at each of one or more frequencies into wavefield energy propagated with respective wavelengths from one or more of transmitter transducer positions, each said transmitter transducer position propagating wavefield energy at at least one orientation defined by Euler angles with respect to a selected fixed coordinate system; (b) for one or more receiver positions each having at least one orientation defined by Euler angles with respect to said selected fixed coordinate system, detecting at each of said one or more receiver positions and respective orientations thereof said wavefield energy; (c) electronically processing said detected wavefield energy so as to transform said detected wavefield energy into one or more reception stored signals stored in said computer memory and corresponding to a scattered wavefield energy detected; (d) setting a region characteristics estimate of selected physical characteristics at selected image points within the region and storing each said region characteristics estimate in said computer memory; (e) performing a convergence step comprising the following steps: (1) preparing, for each said one or more frequencies at each said transmitter transducer positions and respective orientations thereof; an estimate of a total wavefield energy at selected wavefield points derived from a selected incident wavefield energy for a subset of said selected wavefield points stored in the computer memory and said region characteristics estimate for said selected image points by the steps of: (i) designating a primary subset of said selected wavefield points and a different secondary subset of said selected wavefield points, each said selected wavefield point in the primary and secondary subsets of said selected wavefield points being separated from any other by at least one half of a minimum wavelength, wherein the minimum wavelength is the wavelength of the wave field energy in the region at the maximum of said one or more frequencies; (ii) setting the estimate of the total wavefield energy equal to a selected initial total wavefield energy estimate for the primary subset of said selected wavefield points; (iii) computing the estimate of the total wavefield energy on the secondary subset of said selected wavefield points using the region characteristics estimate on the selected image points and the total wavefield energy on the primary subset of said selected wavefield points; (iv) re-designating the primary subset of said selected wavefield points to include a subset of the secondary subset of said selected wavefield points and re-designating the secondary subset of said selected wavefield points to include another subset of the selected wavefield points, each said selected wavefield point in the primary and secondary subsets of said selected wavefield points being separated from any other by at least one half of a minimum wavelength, wherein the minimum wavelength is the wavelength of the wavefield energy in the region at the maximum of said one or more frequencies; and (v) repeating steps ((iii) through ((iv)) until the estimate of the total wavefield energy is computed for each of the selected wavefield points; (2) deriving, for each of said one or more frequencies at each said transmitter transducer position and orientations thereof; a calculated scattered wavefield energy for one or more of said receiver positions and respective orientations thereof from at least one of said region characteristics estimate at said selected image points and said estimate of said total wavefield energy for a corresponding transmitter transducer position and orientations thereof at a portion of said selected wavefield points by performing the steps of: (i) for each selected point of a portion of the selected wavefield points, said portion of the selected wavefield points corresponding to one of said one or more receiver positions and respective orientations thereof; setting said calculated scattered wavefield energy equal to the estimate of the total wavefield energy less said selected incident wavefield energy; and (ii) computing a sum over said portion of said selected wavefield points equal to the sum of the calculated scattered wavefield energy for said portion of said selected wavefield points times a function constructed to correspond to one or more of said one or more receiver positions and respective orientations thereof; (3) for each said transmitter transducer position and orientations thereof and for each said receiver position and orientation thereof comparing said scattered wavefield energy detected to said calculated scattered wavefield energy to derive therefrom a comparator; and (4) when said comparator is greater than a selected tolerance, determining and storing in said computer memory said region characteristics estimate by computing one or more derivatives of the comparator or approximations thereof with respect to one or more of said selected physical characteristics at one or more of said selected image points, and then using said one or more derivatives of the comparator or approximations thereof to compute a region characteristics correction, and then adding said region characteristics correction to each of said region characteristics estimate for each of said one or more of said selected image points, wherein said one or more derivatives of the comparator or approximations thereof is computed from one or more of: (i) at each said one or more frequencies, said estimate of said total wavefield energy for a portion said selected wavefield points for each of said one or more of said transmitter transducer positions and respective orientations thereof; (ii) at each of said one or more frequencies, said calculated scattered wavefield energy for said one or more receiver positions and respective orientations thereof, and for each of said one or more of said transmitter transducer positions and respective orientations thereof; (iii) at each of said one or more frequencies, said scattered wavefield energy detected for said one or more receiver positions and respective orientations thereof and for each of said one or more of said transmitter transducer positions and respective orientations thereof; and (iv) said region characteristics estimate for said selected image points; (f) repeating said convergence step until said comparator is less than or equal to said selected tolerance, and thereafter storing said region characteristics estimate as said image in the computer memory.