Carotid artery segmentation using level set method with double adaptive threshold (DATLS) on TOF-MRA images

Purpose This study aimed to propose a method to semi-automatically segment lumen of carotid artery on TOF-MRA images with well performance on images with weak boundary. Methods The proposed method modified traditional level set method with double adaptive threshold (DATLS). Two thresholds were calculated from probability density function of initial region of interest. Threshold Th1 was used to generate initial contour and threshold Th2 was used to control evolution by modifying energy function of the level set. The performance of the proposed method was tested on TOF-MRA images from CARE II study via using manual delineation as reference. Sixty cases were randomly selected to compare the performance of traditional level set with DATLS, all 283 cases were used to test the robustness of DATLS and 20 cases were used to compare the intra- and inter-operator reproducibility of manual delineation with DATLS. The Dice Similarity Coefficient, Mean Contour Distance and Hausdorff Distance between the proposed method and the manual segmentation were reported. Results Traditional level set failed to segment carotid artery on 13 cases because of over convergence. Compared to traditional level set, DATLS showed a higher DSC (0.88 ± 0.07 vs. 0.75 ± 0.15), lower MCD (0.48 ± 0.37 mm vs. 1.89 ± 2.24 mm) and HD (1.41 ± 1.11 mm vs. 4.59 ± 4.59 mm) in the remaining 47 cases. The average DSC, MCD and HD of DATLS on 283 cases were 0.87 ± 0.09, 0.64 ± 0.87 mm and 1.76 ± 2.23 mm, respectively. Compared to manual delineation, DATLS had better reproducibility on DSC (intra-operator: 0.97 ± 0.09 and inter-operator: 0.97 ± 0.09 vs. intra-operator: 0.91 ± 0.04 and inter-operator: 0.91 ± 0.04), as well as MCD (intra-operator: 0.08 ± 0.18 mm and inter-operator: 0.13 ± 0.52 mm vs. intra-operator: 0.35 ± 0.20 mm and inter-operator: 0.37 ± 0.19 mm) and HD (intra-operator: 0.30 ± 0.66 mm and inter-operator: 0.48 ± 1.38 mm vs. intra-operator: 0.99 ± 0.79 mm and inter-operator: 0.90 ± 0.85 mm). Conclusion Compared to traditional level set, DATLS out-performed on computing time, robustness and accuracy of segmentation on TOF-MRA. The proposed method using modified level set with double adaptive threshold might be a promising tool for lumen segmentation of carotid artery on TOF-MRA.