Image registration method

Claim 2

For use in a digital subtraction method of extracting vascular tracks by conducting subtractions between a first X-ray image before injection of a contrast medium and second X-ray image subsequent to the injection of the contrast medium, an image registration method comprising the steps of: (a) dividing said first and second X-ray images into a plurality of blocks; (b) from each of said blocks extracting a standard point for registration; (c) adjusting positional discrepancies between corresponding blocks of said first and second X-ray images by transforming the coordinates thereof on the basis of the extracted standard point; and (d) modifying the transformed coordinates in prescribed portions of said blocks along respective interfaces thereof with adjacent blocks so as to effect a smoothing of image features connected through said interfaces; wherein said standard point extracting step (b) includes the sub-steps of: determining the difference between said first and second X-ray images; for each of plural picture elements of which said images are comprised comparing the determined difference in each picture element with a predetermined threshold value; and selecting as said standard point the point which remains as a result of the threshold comparison.

Claim 3

For use in a digital subtraction method of extracting vascular tracks by conducting subtractions between a first X-ray image before injection of a contrast medium and second X-ray image subsequent to the injection of the contrast medium, an image registration method comprising the steps of: (a) dividing said first and second X-ray images into a plurality of blocks; (b) from each of said blocks extracting a standard point for registration; (c) adjusting positional discrepancies between corresponding blocks of said first and second X-ray images by transforming the coordinates thereof on the basis of the extracted standard point; and (d) modifying the transformed coordinates in prescribed portions of said blocks along respective interfaces thereof with adjacent blocks so as to effect a smoothing of image features connected through said interfaces; wherein said standard point extracting step (b) includes the sub-steps of: making up first and second histograms respectively corresponding to said first and second X-ray images; determining a curve indicative of the integrated values of the differences between said first and second histograms; and conducting a selection from said second X-ray image by using as said standard point the point which has a lower X-ray strength than that at the peak point of the determined curve.

Claim 4

For use in a digital subtraction method of extracting vascular tracks by conducting subtractions between a first X-ray image before injection of a contrast medium and second X-ray image subsequent to the injection of the contrast medium, an image registration method comprising the steps of: (a) dividing said first and second X-ray images into a plurality of blocks; (b) from each of said blocks extracting a standard point for registration; (c) adjusting positional discrepancies between corresponding blocks of said first and second X-ray images by transforming the coordinates thereof on the basis of the extracted standard point; and (d) modifying the transformed coordinates in prescribed portions of said blocks along respective interfaces thereof with adjacent blocks so as to effect a smoothing of image features connected through said interfaces; wherein said standard point extracting step (b) includes the sub-steps of: making up first and second histograms respectively corresponding to said first and second X-ray images; determining a curve indicative of the integrated values of the differences between said first and second histograms; and conducting a selection from said second X-ray image by using as said standard point the point which has a lower X-ray strength than that at the peak point of the determined curve.

Claim 5

For use in a digital subtraction method of extracting vascular tracks by conducting subtractions between a first X-ray image before injection of a contrast medium and second X-ray image subsequent to the injection of the contrast medium, an image registration method comprising the steps of: (a) dividing said first and second X-ray images into a plurality of blocks; (b) from each of said blocks extracting a standard point for registration; (c) adjusting positional discrepancies between corresponding blocks of said first and second X-ray images by transforming the coordinates thereof on the basis of the extracted standard point; and (d) modifying the transformed coordinates in prescribed portions of said blocks along respective interfaces thereof with adjacent blocks so as to effect a smoothing of image features connected through said interfaces; wherein said standard point extracting step (b) includes the sub-steps of: comparing the positional discrepancy of said standard point, which has been extracted for each divided block, and the positional discrepancy of another standard point, which has been extracted for another block in the neighborhood of said divided block; and removing the standard point which is judged to be singular as a result of said comparison.

Claim 6

For use in a digital subtraction method of extracting vascular tracks by conducting subtractions between a first X-ray image before injection of a contrast medium and second X-ray image subsequent to the injection of the contrast medium, an image registration method comprising the steps of: (a) dividing said first and second X-ray images into a plurality of blocks; (b) from each of said blocks extracting a standard point for registration; (c) adjusting positional discrepancies between corresponding blocks of said first and second X-ray images by transforming the coordinates thereof on the basis of the extracted standard point; and (d) modifying the transformed coordinates in prescribed portions of said blocks along respective interfaces thereof with adjacent blocks so as to effect a smoothing of image features connected through said interfaces; wherein said standard point extracting step (b) includes the sub-steps of: comparing the positional discrepancy of said standard point, which has been extracted for each divided block, and the positional discrepancy of another standard point, which has been extracted for another block in the neighborhood of said divided block; and removing the standard point which is judged to be singular as a result of said comparison.

Claim 7

For use in a digital subtraction method of extracting vascular tracks by conducting subtractions between a first X-ray image before injection of a contrast medium and second X-ray image subsequent to the injection of the contrast medium, an image registration method comprising the steps of: (a) dividing said first and second X-ray images into a plurality of blocks; (b) from each of said blocks extracting a standard point for registration; (c) adjusting positional discrepancies between corresponding blocks of said first and second X-ray images by transforming the coordinates thereof on the basis of the extracted standard point; and (d) modifying the transformed coordinates in prescribed portions of said blocks along respective interfaces thereof with adjacent blocks so as to effect a smoothing of image features connected through said interfaces; wherein said standard point extracting step (b) includes the sub-steps of: correlating said first and second X-ray images for each partial region that is determined by a template having an area varying with the coarseness of the image; and selecting said standard point on the basis of the correlated result.

Claim 8

For use in a digital subtraction method of extracting vascular tracks by conducting subtractions between a first X-ray image before injection of a contrast medium and second X-ray image subsequent to the injection of the contrast medium, an image registration method comprising the steps of: (a) dividing said first and second X-ray images into a plurality of blocks; (b) from each of said blocks extracting a standard point for registration; (c) adjusting positional discrepancies between corresponding blocks of said first and second X-ray images by transforming the coordinates thereof on the basis of the extracted standard point; and (d) modifying the transformed coordinates in prescribed portions of said blocks along respective interfaces thereof with adjacent blocks so as to effect a smoothing of image features connected through said interfaces; wherein said standard point extracting step (b) includes the sub-steps of: correlating said first and second X-ray images for each partial region that is determined by a template having an area varying with the coarseness of the image; and selecting said standard point on the basis of the correlated result.