Fig. 4From: Decoding intra-tumoral spatial heterogeneity on radiological images using the Hilbert curvea The lung tumor used to illustrate the three-dimensional (3D) Hilbert curve expansion. b The Hilbert volume with level 6 defined in this study, and the lung tumor (in blue) encapsulated in the Hilbert volume according to the 3D coordinates. c The empty Hilbert matrix to store the result of dimensionality reduction from (b)Back to article page