Brief communication: Limitations of medical X-ray computed tomography for estimating ice content in permafrost samples

X-ray Computed tomography (CT) is increasingly used to estimate ice contents in permafrost samples. In this study, CT-derived estimates of volumetric ice content obtained from medical CT scans were compared with laboratory measurements for 261 samples from northern Canada (Nunavut and Yukon). The results shows that medical CT systematically underestimates ice content in sediment-rich and organic-poor samples, and overestimated it in ice-rich, organic-rich samples. Agreement improves only when ice contents exceeded ∼75 % and organic matter was approximately 10 % to 20 %. These discrepancies arise from ice occurring at scales smaller than the CT voxel resolution, misclassification of organic matter as ice, and sensitivity to threshold selection. Given these limitations, along with the associated cost and processing effort, medical CT is better suited for visualizing cryostructures and sample heterogeneity than for routine quantification of ice content. While higher-resolution CT systems may help resolve some of these limitations, their ability to provide more accurate quantification in permafrost samples requires further investigation and is identified as a key direction for future research.