The present invention relates to hydrogels comprising 1,2-diol or 1,3-diol groups acetalised with a radiopaque species of one or more covalently bound radiopaque halogens which are imageable during embolization therapy. A steerable endoscope is described having an elongate body with a manually or selectively steerable distal portion, an automatically controlled portion, a flexible and passively manipulated proximal portion, and an externally controlled and manipulatable tracking rod or guide. The data storage device may display, on the visual display, an indication that a data storage medium of the data storage device has been securely erased. Also disclosed are methods for the oxidative chemocatalytic conversion of carbohydrates to carboxylic acids or derivatives thereof. The features serve as inputs to a classifier, which can be a computer program, a device or both.