Surface topography index: a novel deformity severity assessment index for pectus excavatum

BACKGROUND: The surface topography index (STI) has great potential in both routine computed tomography (CT) scan and emerging optical imaging systems. However, the diagnostic accuracy and stability of the STI as a deformity severity assessment index has not been fully confirmed. Therefore, the aim of the present study was to determine the diagnostic performance of the STI as a novel deformity severity assessment index for pectus excavatum. METHODS: The present study consisted of 722 chest CT images from a single center. The standard CT index (CTI) and STI were calculated for all patients. The between-group difference and the level of compliance between the CTI and STI was analyzed by t-test and Pearson correlation. The diagnostic value and optimum discriminatory values of the CTI and STI were calculated by a receiver-operating characteristic (ROC) curve and DeLong’s test. RESULTS: The distributions of the CTI and STI were similar and showed a slight overlap between the pectus excavatum (PE) and non-PE groups. Both the CTI and STI significantly differed between the 2 groups (P<0.001). The STI demonstrated a strong Pearson correlation with the CTI (r=0.91, 95% confidence interval: 0.88–0.91, P<0.001). The ROC curves showed that STI =1.58 (sensitivity: 0.93, specificity: 0.95) could be considered equivalent to CTI =2.72 (sensitivity: 0.93, specificity: 0.97) as the optimum discriminatory values. DeLong’s test showed no significant difference in the ROC curve results between the CTI and STI (Z=0.90, P=0.37). CONCLUSIONS: The STI has comparative discrimination ability in PE diagnosis and deformity severity assessment when used with the standard CTI. The STI as a novel index is not only an ideal evaluation metric of PE deformity but also an objective trait for PE patients just as weight and height for everyone.