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: Angiography and intracoronary ultrasound demonstrated lack of contact between stent and vessel wall in a 15 - mm long segment with maximal aneurysm diameter of 6 . 0 mm .
### Output Text:
Angiography and intracoronary ultrasound demonstrated lack of contact between stent and vessel wall in a 15 - mm long segment with maximal aneurysm diameter of 6 . 0 mm . 