Fig. 4.

A: Diagram for the re-positioning of the animal. Each air-breathing imaging session started at approximately 5, 20 and 35 min after placing the animal in the water tank of the MSOT system. Air-breathing imaging takes approximately 2 min. The air is then changed for 100%-O₂, for 2 min and the same tumour region is re-imaged for approximately 2 min again, during O₂-breathing. B: sO₂ distributions or ‘oxymaps’ of 4 CAL^R tumours, positioned differently by remounting the animals 3 times in the MSOT tank with the minimum time interval between each imaging session. The ‘oxymaps’ are shown as overlays on greyscale photoacoustic images, of the central slice of each tumour. B: body; W: water. Yellow bar represents a 10 mm size scale.