In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: DWI findings in this cohort are indicative of cytotoxic oedema within cerebral white matter and lend support to an at least partially reversible metabolic derangement as the basis for this syndrome .
### Output Text:
DWI findings in this cohort are indicative of cytotoxic oedema within cerebral white matter and lend support to an at least partially reversible metabolic derangement as the basis for this syndrome . 