Fast-marching contours for the segmentation of vessel lumen in CTA cross-sections

This work deals with the segmentation of the arterial lumen in cross-sections of CT angiography (CTA) images, by means of active contours. Within the context of the fast-marching method, a new speed-control function is proposed in order to cope with strongly variable contrasts along the perimeter of the contour. This function was devised to guarantee the existence of a time T at which the fast-marching front fits the actual boundary of the vessel lumen, despite calcifications and other neighboring structures. Instead of using the magnitude of the image intensity gradient alone, this function includes exponential factors that strongly decrease the propagation speed when the front moves beyond the local maxima of the gradient magnitude and beyond the range of luminal intensities in CTA images. The propagation is stopped when the the growth of the area A encompassed by the front becomes very slow, which is characterized by a large value of dT/dA. The segmentation was evaluated in 65 cross-sections of carotid arteries from 13 different patients, by comparison with contours traced by a radiologist. The mean sensitivity was 0.849 and the mean positive predictive value was 0.797.