34 Chapter 2 2.8 SUPPLEMENTARY MATERIAL S.2.8.1. Definition of shape descriptors. Shape marker Formula WMH type Comment Convexity (C) C= Convex Hull Area Area Periventricular/ Confluent WMH Convexity and Solidity describe how concave or convex the shape is. A maximally convex shape has a convexity and solidity value of 1. The values decrease with a more concave, complex shape. Solidity (S) S= Volume Convex Hull Volume Periventricular/ Confluent WMH Concavity Index (CI) CI C S = (2− ) +(1− ) 2 2 Periventricular/ Confluent WMH As a measure of roughness, concavity index describes how dense, irregular or elongated and curved a lesion is. Higher CI values suggest a more complex WMH shape. Fractal Dimension (FD) ( ) FD n = lim log( ) log r r r →1 1 n = number of boxes r = box size Periventricular/ Confluent WMH Deep WMH Textural roughness is measured using the Minkowski-Bouligand dimension (box counting dimension). Higher FD values suggest a more complex WMH shape. Eccentricity (E) E Minor Axis Major Axis = Major axis: largest diameter in 3D space. Minor axis: smallest diameter orthogonal to the major axis. Deep WMH Eccentricity assesses the deviation from a circle. The eccentricity of a circle is 1 and the eccentricity of a line is 0. S.2.8.2. The association between age, sex, and WMH shape markers. Age Sex Periventricular/Confluent WMH† Solidity‡ 0.02 (-0.04–0.00) -0.21 (-0.41–-0.01)* Convexity -0.01 (-0.02–-0.00)* -0.00 (-0.11–0.11) Concavity index‡ 0.01 (0.00–0.01)** 0.02 (-0.03–0.08) Fractal dimension 0.01 (0.0–0.02)*** 0.01 (-0.06–0.08) Deep WMH Eccentricity 0.00 (-0.00–0.00) 0.04 (-0.01–0.08) Fractal dimension -0.00 (-0.01–0.00) 0.00 (-0.11–0.11) The values represent B values (95% confidence interval) of the linear regression. * p<0.05. ** p<0.01. *** p<0.001. ‡ Solidity and concavity index were multiplied by 100 and natural log transformed, due to non-normal distribution. † Periventricular/confluent WMH with a volume >4 ml. Periventricular/confluent WMH: n=73; Deep WMH: n=122.
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