Fig. 4. Acidic margin-guided brain tumor surgery in live rat models. (A) Preoperative T2W-MR image of rat brain bearing C6 orthotopic allografts. The tumor was indicated by a white arrow. (B) In vivo CEST-pH map of a rat brain model. (C) Illustration indicating the surgical location before the craniotomy. (D) Sequential white light images (left panel), intra-operatively collected Raman spectra (middle panel) and a pH topographic map (right panel) of the resection bed. Yellow dashed boxes marked the area with detectable SERRS signals and star symbols presented the points with the highest acidity.