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This paper presents the forward and inverse

The traditional formulation of segmentation of images using active contours with edges exhibits an inherent shortcoming: when the boundaries between skin and lesions is smooth, edge based features tend to give poor segmentation results. An alternative formulation of active contours using structure tensor is proposed in which creasness features (peaks and valleys) are used for the determination of lesion boundaries, which enhance directional gradients while inhibiting local texture attributes in the images. The creasness features are used for formulation of external energy term in the active contour framework to segment dermoscopy images. Experiments show that the proposed segmentation method exhibits good performance comparing favorably to the traditional edge based active contour formulation.

The aim of this study is to compare the absorbed doses of critical organs of 131I using the MIRD (Medical Internal Radiation Dose) with the corresponding predictions made by GEANT4 simulations. S-values (mean absorbed dose rate per unit activity) and energy deposition per decay for critical organs of 131I for various ages, using standard cylindrical phantom comprising water and ICRP soft-tissue material, have also been estimated. In this study the effect of volume reduction of thyroid, during radiation therapy, on the calculation of absorbed dose is also being estimated using GEANT4. Photon specific energy deposition in the other organs of the neck, due to 131I decay in the thyroid organ, has also been estimated. The maximum relative difference of MIRD with the GEANT4 simulated results is 5.64% for an adult's critical organs of 131I. Excellent agreement was found between the results of water and ICRP soft tissue using the cylindrical model. S-values are tabulated for critical organs of 131I, using 1, 5, 10, 15 and 18 years (adults) individuals. S-values for a cylindrical thyroid of different sizes, having 3.07% relative differences of GEANT4 with Siegel & Stabin results. Comparison of the experimentally measured values at 0.5 and 1 m away from neck of the ionization chamber with GEANT4 based Monte Carlo simulations results show good agreement. This study shows that GEANT4 code is an important tool for the internal dosimetry calculations.