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: Diffusion weighted imaging ( DWI ) of all patients revealed well demarcated hyperintense lesions within the subcortical white matter of the cerebral hemispheres and the corpus callosum , corresponding to areas of decreased proton diffusion on apparent diffusion coefficient ( ADC ) maps ( available in 21 / 27 patients ) .
### Output Text:
Diffusion weighted imaging ( DWI ) of all patients revealed well demarcated hyperintense lesions within the subcortical white matter of the cerebral hemispheres and the corpus callosum , corresponding to areas of decreased proton diffusion on apparent diffusion coefficient ( ADC ) maps ( available in 21 / 27 patients ) . 