Sugar maple (Acer saccharum) develops elevated pressures in response to repeated cycles of freezing and thawing. This pressure is theorised to develop due to compression of gas present within fibres. Due to surface tension the pressurised gas within fibres should rapidly dissolve. That the gas persists over time is believed to be due to an osmotic barrier present between fibres and vessels that prevents sucrose from diffusing into fibres. This creates sufficient osmotic pressure to prevent gas dissolution and so maintain fibre embolisms. In our work we examine this hypothesis using synchrotron based microCT to produce high-resolution three-dimensional images of stem segments. Using this technique, we directly resolved the gas present in the fibres. Subsequently we perfused stem segments with either water or 2% sucrose and re-imaged them to examine any changes in fibre embolisms. Additionally, we also looked at samples that were frozen for 2-3 months to promote fibre embolism development, and for comparison we look at paper birch (Betula pendula), a species that is thought to develop elevated stem pressures through a different mechanism than Acer. From the fresh stem segments, we observed fibre embolisms were indeed present, and that when perfused with sucrose solution there was little to no change in fibre embolisms, whereas in almost all cases perfusing with water led to partial or complete refilling of fibre embolisms, supporting the hypothesis. The frozen samples did not display complete xylem embolization, in contrast to expectations, and showed complete refilling upon perfusion with either solution, suggesting cell damage had occurred. The birch samples also showed fibre embolisms. These embolisms remained after perfusing with sucrose solution, and there was some evidence the fibre embolisms refilled upon perfusion with water, however more samples are required to confirm these observations.