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Techniques for accelerated elastic registration include receiving reference scan data and floating scan data, and a first transformation for mapping coordinates of scan elements from the first scan to coordinates of scan elements in the second scan. A subset of contiguous scan elements is determined

Techniques for accelerated elastic registration include receiving reference scan data and floating scan data, and a first transformation for mapping coordinates of scan elements from the first scan to coordinates of scan elements in the second scan. A subset of contiguous scan elements is determined. At least one of several enhancements is implemented. In one enhancement cubic spline interpolation is nested by dimensions within a subset. In another enhancement, a local joint histogram of mutual information based on the reference scan data and the floating scan data for the subset is determined and subtracted from an overall joint histogram to determine a remainder joint histogram. Each subset is then transformed, used to compute an updated local histogram, and added to the remainder joint histogram to produce an updated joint histogram. In another enhancement, a measure of similarity other than non-normalized mutual information is derived from the updated joint histogram.

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1. A method for elastic registration of multiple scans of internal properties of a body, comprising the steps of: receiving control point transformation data that indicates a vector φ of values for transform parameters for each control point of a plurality of control points that correspond to scan e

1. A method for elastic registration of multiple scans of internal properties of a body, comprising the steps of: receiving control point transformation data that indicates a vector φ of values for transform parameters for each control point of a plurality of control points that correspond to scan elements in a reference scan, wherein the vector φ of values for transform parameters for a particular control point indicates how to associate the particular control point with one or more scan elements in a floating scan different from the reference scan, andevery scan element in the reference scan has a position indicated by a plurality of coordinate values for a corresponding plurality of dimensions;determining a plurality of subsets of contiguous scan elements in the reference scan, wherein each subset of contiguous scan elements is associated with only one control point;determining on a processor an output vector v of values for transform parameters for each scan element in a first subset of scan elements of the reference scan, including the steps of determining a first cubic B-spline coefficient coef1=ΣB(w1) φ for a first coordinate value of a scan element in the first subset a distance w1 from a control point along a first dimension of the plurality of dimensions summed over four control points, anddetermining a plurality of cubic B-spline coefficients coef2=ΣB(w2) coef1 for a corresponding plurality of coordinate values of a plurality of scan elements in the first subset a distance w2 from a control point along a different second dimension of the plurality of dimensions each summed over four control points, anddetermining v based at least in part on coef2 for each scan element in the first subset; andafter determining the output vector v of values for each scan element in the first subset, then determining on a processor the output vector v of values for each scan element in a different second subset of scan elements of the reference scan,wherein B(n) is a well known function for contributions at an arbitrary point from a control point at a normalized distance n=d/s where d is distance from the control point to the arbitrary point and s is separation of adjacent control points that straddle the arbitrary point. 2. A method as recited in claim 1, wherein the vector φ of values for transform parameters contains values of shifts in a plurality of Cartesian dimensions. 3. A method as recited in claim 1, wherein the vector φ of values for transform parameters includes values of rotation in a plurality of quaternion dimensions. 4. A method as recited in claim 3, said step of receiving control point transformation data further comprising receiving control point transformation data for fewer than four control points in each dimension of the reference scan for determining an output vector of values for transform parameters for each scan element in a subset of scan elements of the reference scan after the initial subset. 5. A method as recited in claim 1, said step of receiving control point transformation data further comprising receiving control point transformation data for four control points in each dimension of the reference scan for determining an initial output vector of values for transform parameters for each scan element in an initial subset of scan elements of the reference scan. 6. A method as recited in claim 1, wherein: said step of determining the output vector v of values for transform parameters for each scan element in the first subset further comprises determining for each value of coef2 a plurality of cubic B-spline coefficients coef3=ΣB(w3) coef2 for a corresponding plurality of coordinate values of a plurality of scan elements in the first subset a distance w3 from a control point along a different third dimension of the plurality of dimensions each summed over four control points, andsaid step of determining v based at least in part on coef2 for each scan element in the first subset further comprises determining v based at least in part on coef3. 7. A method as recited in claim 1, further comprising transforming a treatment plan for the body based at least in part on the output vector v of values for each scan element in the first subset. 8. An apparatus for elastic registration of multiple scans of internal properties of a body, comprising: a computer-readable memory for storing control point transformation data that indicates a vector φ of values for transform parameters for each control point of a plurality of control points that correspond to scan elements in a reference scan, wherein the vector φ of values for transform parameters for a particular control point indicates how to associate the particular control point with one or more scan elements in a floating scan different from the reference scan, andevery scan element in the reference scan has a position indicated by a plurality of coordinate values for a corresponding plurality of dimensions;a first logic circuit, including a first register, configured for determining and storing in the first register, for a first subset of contiguous scan elements in the reference scan, a first cubic B-spline coefficient coef1=ΣB(w1) φ for a first coordinate value of a scan element in a distance w1 from a control point along a first dimension of the plurality of dimensions summed over four control points; anda second logic circuit, including a second register, configured for reading the first register and determining a plurality of cubic B-spline coefficients coef2=ΣB(w2) coef1 for a corresponding plurality of coordinate values of a plurality of scan elements in the first subset a distance w2 from a control point along a different second dimension of the plurality of dimensions each summed over four control points and storing the each coef2 value in succession in the second register,wherein the reference scan includes a plurality of subsets of contiguous scan elements in the reference scan and each subset is associated with only one control point, andB(n) is a well known function for contributions at an arbitrary point from a control point at a normalized distance n=d/s where d is the distance from the control point to the arbitrary point and s is the separation of adjacent control points that straddle the arbitrary point. 9. An apparatus as recited in claim 8, further comprising: a third logic circuit, including a third register, configured for reading the second register and determining for each value of coef2 a plurality of cubic B-spline coefficients coef3=ΣB(w3) coef2 for a corresponding plurality of coordinate values of a plurality of scan elements in the first subset a distance w3 from a control point along a different third dimension of the plurality of dimensions each summed over four control points and storing the each coef3 value in succession in the third register. 10. An apparatus as recited in claim 9, further comprising one or more logic circuits configured for storing the successive values in the third register in computer readable memory in association with each scan element in the reference scan. 11. An apparatus as recited in claim 9, wherein the first logic circuit contains three field programmable gate array (FPGA) multipliers, the second logic circuit contains six FPGA multipliers and the third logic circuit contains twelve FPGA multipliers. 12. An apparatus as recited in claim 8, wherein at least one of the first logic circuit and the second logic circuit is a programmed field-programmable gate array (FPGA). 13. An apparatus as recited in claim 8, wherein at least one of the first logic circuit and the second logic circuit further comprises a look-up table (LUT) for values of B(n) for a plurality of values of n. 14. An apparatus as recited in claim 8, wherein the computer-readable memory is a static random access memory (SRAM). 15. An apparatus as recited in claim 8, further comprising one or more logic circuits configured for storing the successive values in the second register in computer-readable memory in association with each scan element in the reference scan. 16. An apparatus as recited in claim 8, further comprising one or more logic circuits configured for associating one or more scan elements in the floating scan with the reference scan based at least in part on contents of the second register. 17. An apparatus as recited in claim 8, further comprising: one or more processors; anda computer readable-medium holding one or more sequences of instructions wherein execution of the one or more sequences of instructions by one or more processors causes the one or more processors to perform the step of transforming a treatment plan for the body based at least in part on the second transformation. 18. An apparatus as recited in claim 8, further comprising one or more logic circuits configured for determining a value for a measure of similarity between the reference scan and the floating scan based at least in part on the contents of the second register. 19. An apparatus as recited in claim 8, further comprising a single processor configured to perform in less time than three minutes automatic elastic registration that maximizes a similarity measure based on substantively every scan element in a region of overlap between two scans each having 256×256×256 scan elements. 20. An apparatus for elastic registration of multiple scans of internal properties of a body, comprising: a computer-readable medium for storing: a two dimensional first joint histogram of mutual information based on reference scan data and floating scan data for a plurality of scan elements; andsubvolume data that indicates a subset of contiguous scan elements of the plurality of scan elements,wherein reference scan data indicates for the plurality of scan elements a corresponding plurality of intensity values based on a first scan of the body,floating scan data indicates for the plurality of scan elements a corresponding plurality of intensity values based on a different second scan of the body and a first transformation for mapping coordinates of scan elements from the first scan to coordinates of scan elements in the second scan, andthe joint histogram indicates a number of the plurality of scan elements that have intensity values based on the first scan in a first range of intensities and have intensity values based on the second scan in a second range of intensities;a logic circuit configured for determining a local joint histogram of mutual information based on the reference scan data and the floating scan data for the subset of contiguous scan elements;a logic circuit configured for determining a remainder joint histogram of mutual information by subtracting the local joint histogram from the first joint histogram and storing the remainder joint histogram on the computer-readable medium; anda logic circuit configured for determining a value for a similarity measure, based at least in part on the remainder joint histogram, for a second transformation for mapping coordinates of the subset of scan elements from the first scan to coordinates of scan elements in the second scan. 21. An apparatus for elastic registration of multiple scans of internal properties of a body, comprising: a computer-readable medium for storing a two dimensional joint histogram of mutual information based on reference scan data and floating scan data for a plurality of scan elements wherein reference scan data indicates for the plurality of scan elements a corresponding plurality of intensity values based on a first scan of the body,floating scan data indicates for the plurality of scan elements a corresponding plurality of intensity values based on a different second scan of the body and a first transformation for mapping coordinates of scan elements from the first scan to coordinates of scan elements in the second scan, andthe joint histogram indicates a number of the plurality of scan elements that have intensity values based on the first scan in a first range of intensities and have intensity values based on the second scan in a second range of intensities; anda logic circuit configured for determining based on the joint histogram a measure of similarity for the reference scan data and the floating scan data, wherein the measure of similarity is not mutual information,whereby an elastic transformation can be determined based on the measure of similarity.