CA9 and neoplasm: Finally, levels of hypoxia in the tumours, measured by CAIX IHC, positively correlated in both AT+VF and RF methods with skeletonised blood volume (r = 0.72, p = 0.007; and r = 0.72, p = 0.004, respectively), number of edges (r = 0.59, p = 0.04; and r = 0.84, p < 0.001, respectively), nodes (r = 0.72, p = 0.007; and r = 0.84, p < 0.001, respectively) and looping structures (r = 0.61, p = 0.03; and r = 0.85, p < 0.001, respectively).