Support value based stent-graft marker detection

With the development of the fluoroscopic roentgenographic stereophotogrammetric analysis (FRSA), it is possible to make the three-dimensional (3D) dynamics of stent-graft. The stent-graft markers, however, are identified manually. In this paper we present a robust solution for automatic detection of stent-graft marker projections in FRSA X-ray images. Several directional support value (dSV) filters and the directional support value transform (dSVT) method are studied. Based on the dSV of the dSVT, a support value matrix is constructed, and the determinant of this matrix is then defined as the markerness measure. The corresponding multi-scale correlations of the rescaled markerness measures are computed for enhancing the multi-scale marker response peaks while suppressing the effects of stent-grafts and Poisson noise. The marker spots are subsequently located by finding the local maximum of the correlated markerness measures. The conditional variance Stabilizer (CVS) is further integrated into this framework for removing Poisson noises. Performance comparisons are carried out among the proposed dSVT, the CVS+dSVT, local threshold operation (LTO) and the frequently adopted spot detectors, including the morphological grayscale opening top-hat filter (MTH), wavelet multiscale products (WMP), and multiscale variance-stabilizing transform (MSVST) methods. The results from experiments on synthetic as well as real FRSA X-ray image data show that the proposed CVS+dSVT method performs better than other detectors, in terms of the free-response receiver operation characteristic (FROC) curves.