Abstract
Digital subtraction angiography has been accepted as an invaluable clinical tool over the past decade; however, film-screen-based angiography is still performed routinely when high-resolution or large field-of-view angiograms are needed. A technique is presented whereby two films from an angiographic sequence are digitized using a high-resolution laser digitizer, and the digitized images are aligned, subtracted, and displayed using the computer. To accommodate for some types of patient motion, an image warping algorithm is presented and discussed in detail. The warping algorithm is piecewise linear, using triangular regions for warping, resulting in a global nonlinear transform across triangle elements. An algorithm describing optimal triangle selection also is discussed. The results show that subtraction images of excellent quality can be produced by the proposed technique, and suggest that, in some settings, digitized subtraction films may be preferred over conventional film subtraction.
Key Words: angiography, film subtraction, warping algorithm, digital image processing, image registration
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Footnotes
This research was supported in part by grant DAMD17-94-J-4424 from the United States Army Breast Cancer Research Program (the warping algorithm was developed for that project), and by a gift from the Lumisys Corporation. The general concepts behind the warping algorithm were originally conveyed to the authors in past collaborations with Dr William A. Barrett, currently at Brigham Young University. The authors acknowledge his previous contribution.
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