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: Volumetric BMD of the ultradistal radius was measured using peripheral quantitative computed tomography , and areal BMD of the lumbar spine was estimated using dual - energy x - ray absorptiometry .
### Output Text:
Volumetric BMD of the ultradistal radius was measured using peripheral quantitative computed tomography , and areal BMD of the lumbar spine was estimated using dual - energy x - ray absorptiometry . 