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: Thallium - 201 SPECT demonstrated a perfusion defect in all 14 dogs analyzed during dipyridamole - induced hyperemia ; the size of the perfusion defect correlated with the anatomic area at risk ( r = 0 . 58 ; p less than 0 . 03 ) and with the perfusion defect by contrast echocardiography ( r = 0 . 58 ; p less than 0 . 03 ) .
### Output Text:
<span class="chemical">Thallium</span> - 201 SPECT demonstrated a perfusion defect in all 14 dogs analyzed during <span class="chemical">dipyridamole</span> - induced hyperemia ; the size of the perfusion defect correlated with the anatomic area at risk ( r = 0 . 58 ; p less than 0 . 03 ) and with the perfusion defect by contrast echocardiography ( r = 0 . 58 ; p less than 0 . 03 ) . 