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: OBJECTIVES : To assess the added diagnostic value of a new cardiac performance index ( dP / dtejc ) measurement , based on brachial artery flow changes , as compared to standard 12 - lead ECG , for detecting dobutamine - induced myocardial ischemia , using Tc99m - Sestamibi single - photon emission computed tomography as the gold standard of comparison to assess the presence or absence of ischemia .
### Output Text:
OBJECTIVES : To assess the added diagnostic value of a new cardiac performance index ( dP / dtejc ) measurement , based on brachial artery flow changes , as compared to standard 12 - lead ECG , for detecting <span class="chemical">dobutamine</span> - induced myocardial ischemia , using <span class="chemical">Tc99m - Sestamibi</span> single - photon emission computed tomography as the gold standard of comparison to assess the presence or absence of ischemia . 