Reference Column in Datatable

Hi

I have the following code below and would like to know how I can reference the column UserName in the FOREACH statement so I can manipulate the value.  

Many thanks

$SqlConnectionString = "Data Source=HALLW2678\SQL2012ENT;Initial Catalog=Printers;Trusted_Connection=Yes"
$SqlConnection = new-object system.data.SqlClient.SqlConnection($SqlConnectionString);
$SqlCmd = New-Object System.Data.SqlClient.SqlCommand
$SqlCmd.CommandText = ("SELECT UserName FROM dbo.Fujitsu")
$SqlCmd.Connection = $SqlConnection
$SqlAdapter = New-Object System.Data.SqlClient.SqlDataAdapter
$SqlAdapter.SelectCommand = $SqlCmd
$DataSet = New-Object System.Data.DataSet
$SqlAdapter.Fill($DataSet)
$SqlConnection.Close()
$data = $dataset.Tables[0]

foreach ($dataitem in $data.Rows)
{	
	
	Write-Host "Name is: " $dataitem
}