Geometric distortion of digital angiography image

Digital angiography remains valuable in a diagnostic environment where anatomical definition is important. However it is not sufficiently reliable in circumstances (such as stereotactic application) where precise geometry is important. The geometric distortion of digital angiography is mainly caused by the inherent, non-uniform electromagnetic field of the Image Intensifier board. In this paper we quantify this distortion so as to evaluate its clinical relevance. We utilize image fusion with fiducial markers and image exploration with cursor projection in this investigation. Fiducial markers on the images were normalized first and then used as baselines to scale and orient the corresponding images so they could be accurately registered, superimposed, and subtracted. Image exploration with cursor projection allowed for easy identification of the same point on corresponding images, which provided quantitative evaluation of geometric differences between digital and analogue angiography images. Based on our study, we concluded: 1) Compared with MRI geometric distortion of as much as 2 mm, digital angiography is clinically appropriate for stereotactic application; 2) With an improved test object (reducing the vertical and horizontal lines which form the square grids from the current thickness of 0.8 mm), the results would be more accurate.