c# - Updating Datagrid datacontext eats memory -

i have wpf datagrid , need update every minute. have added dispatchtimer data , update data context of datagrid. problem seems data sticking around. first thinking lists had lists running out updated datacontext , don't see megs of memory being used.

        dispatchertimer dispatchertimer = new dispatchertimer();         dispatchertimer.tick += new eventhandler(dispatchertimer_tick);         dispatchertimer.interval = new timespan(0, 0, 1); 

i have set 1 second testing.

    private void dispatchertimer_tick(object sender, eventargs e)     {         observablecollection<technician> techdata = loaddata();         dg1.datacontext = null;         dg1.datacontext = techdata;     } 

...

    private observablecollection<technician> loaddata()     {         observablecollection<technician> techdata = new observablecollection<technician>();          uri urigreenimage = new uri("pack://application:,,,/images/green.png");         uri uriredimage = new uri("pack://application:,,,/images/red.png");          // connect database.         database db = new database();          string query = "select * dbo.statusboard order dbo.statusboard.lastname";          sqldatareader reader = db.query(query);          while (reader.read())         {             bitmapimage statusimage;              switch(reader["status"].tostring())             {                 case "0":                     statusimage = new bitmapimage(urigreenimage);                     break;                 case "1":                     statusimage = new bitmapimage(uriredimage);                     break;                 default:                     statusimage = new bitmapimage(uriredimage);                     break;             }              techdata.add(new technician             {                 fullname = reader["firstname"].tostring() + " " + reader["lastname"].tostring(),                 comments = reader["comments"].tostring(),                 status = statusimage,                 watchingservicedesk = (reader["watchingservicedesk"].tostring() == "1" ? true : false),                 phone = reader["phone"].tostring()             });         }          return techdata;     }