php - How to make part of regex pattern optional? -

im working regex pattern:

|img_class.*?<img src="(.*?)"(.*?)<\/td>|ms 

but want make <img src="(.*?)" optional (not src part), because img_class td empty , when pattern fails.

i tried |img_class.*?(<img src="(.*?)")?(.*?)<\/td>|ms never match.

(i know use xpath or better im using pretty big class , dont want recode right now).

|img_class.*?(?:<img src="(.*?)")?(.*?)<\/td>|ms