Data analysis
Data are indicated as mean ± standard deviation (SD) (Gaussian distribution) or median (range) (Skewed distribution) for continuous variables and as numbers and percentages for categorical variables.χ 2 (categorical variables), student t-test (normal distribution) were used to detect the differences among different FET lengths (binary variable). Categorical variables were compared across groups using Fisher’s exact test. Values were considered statistically significant when P <0.05. All the analyses were performed with the statistical software packages R (http://www.R-project.org, The R Foundation) and EmpowerStats (http://www. empowerstats.com, X&Y Solutions, Inc, Boston, MA).