How to build Acronyms of a phrase in PHP

[Acilskinc]

HiI'm looking for a way that I can extract the first letter of each word from an input field and place it into a variable.Example: if the input field is \[code\]"Stack-Overflow Questions Tags Users"\[/code\] then the output for the variable should be something like \[code\]"SOQTU"\[/code\] Any help is appreciated.Thanks