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MEASUREMENT OF THE SHAPE OF OXALATE CRYSTALS BY AUTOMATED OPTICAL IMAGE ANALYSIS

Bekker AV, McShane J, Vassallo JD, Bedell D, Li TS, Livk I

A new automated static optical image analysis (SOIA) method was developed for characterising the shape of sodium oxalate crystals by separately measuring their length and width. The automated SOIA technique combines crystal image acquisitioning with a custom-developed numerical algorithm for morphological analysis of crystals. The automation of the two main measuring steps enables characterisation of a large number of oxalate crystals ensuring statistically meaningful results. As part of the numerical algorithm, a rectangularity-based morphological fi lter was implemented to eliminate overlapping crystals and crystal networks. The developed optical sizing technique has a low detection limit of 0.25 μm, which is close to the theoretical resolution of optical microscopy. It is demonstrated that the new automated SOIA sizing technique is very sensitive in identifying oxalate crystals of diff erent shape. The SOIA measured crystal size distributions were compared to those obtained by the AccuSizer sizing instrument to confi rm that they were consistent with the measurements obtained by a conventional crystal sizing instrument.