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: In all patients , computerized tomographic ( CT ) brain scans demonstrated stability in tumor size and peritumor edema when compared with pretransplant scans .
### Output Text:
In all patients , computerized tomographic ( CT ) brain scans demonstrated stability in tumor size and peritumor edema when compared with pretransplant scans . 