Sample data for the extension (based on RESECT[1], contains one pre-op MR and three intra-op US images).
[1] Xiao, Yiming, et al. "REtroSpective Evaluation of Cerebral Tumors (RESECT): A clinical database of pre‐operative
MRI and intra‐operative ultrasound in low‐grade glioma surgeries." Medical physics 44.7 (2017): 3875-3882.