Endoscopy with biopsy 31625 & 31636 or 31628?

An endoscopist did a bronscopy with biospy of the walls of the left lobe bronchus and left mainstem bronchus, dilation of the left mainstem bronchus and placement of a bronchial stent in the left mainstem brochus. In the 2011 CPT® code book page 112, I'm trying to determine what the difference between flexible or rigid on CPT® 31625 and transbronchial 31628. Can you please explaination on in the difference to select the correct code for this procedure? Thank you for your help! :)