The active contour model has good performance in boundary extraction for medical images; particularly, Gradient Vector Flow (GVF) active contour model shows good performance at concavity convergence and insensitivity to initialization, yet it is susceptible to edge leaking, deep and narrow concavities, and has some issues handling noisy images. This paper proposes a novel external force, called Iterative Weighted Average Diffusion (IWAD), which used in tandem with parametric active contours, provides superior performance in images with high values of concavity. The image gradient is first turned into an edge image, smoothed, and modified with enhanced corner detection, then the IWAD algorithm diffuses the force at a given pixel based on its 3x3 pixel neighborhood. A forgetting factor, φ, is employed to ensure that forces being spread away from the boundary of the image will attenuate. The experimental results show better behavior in high curvature regions, faster convergence, and less edge leaking than GVF when both are compared to expert manual segmentation of the images.
PWO crystals were grown using the Czochralski method with concentrations from 0.2% to 4%. The polarized optical
absorption, emission, and kinetics of fluorescence were measured at room temperature and low (14K) over a spectral
range of 0.2 to 3 microns. The spectroscopic data were then used to calculate the absorption and luminescence cross
sections. The maximum absorption cross at 4I13/2→4I15/2 transition section was calculated to be σ=8.0x10-21 cm2 at 1500
nm and E||z polarization of incident light. The measured luminescence lifetime at this transition was 5.6 ms.
PbWO4 crystals with Ho concentration ranging from 0.2% to 4% were grown by the Czochralski method. Polarized
optical absorption, emission and kinetics of fluorescence were studied over 20-300K temperature and 0.2-8&mgr;m spectral
ranges. Stimulated Raman scattering in PbWO4 crystal was studied under 1.6 and 2.0 &mgr;m excitation.