Does anyone know a way to get a specific item of a specific topic of the WMI Classes ?

For instance getting the UserName information from Win32_ComputerSystem. The only way I know how to get that info is
Code:

$strComputer = "."
$objWMIService = GetObject("winmgmts:\\" + $strComputer + "\root\cimv2")
$colItems = $objWMIService.ExecQuery("Select * from Win32_ComputerSystem",,48)
For each $objItem in $colItems
  ?  "UserName: " + $objItem.UserName
Next

Isn't it possible to do something like
Code:

$strComputer = "."
$objWMIService = GetObject("winmgmts:\\" + $strComputer + "\root\cimv2")
$Uname = $objWMIService.Get("Win32_ComputerSystem.UserName",0,"")
? $Uname


Any help would be apreciated.