Use Enumerable.Select<TSource, TResult> Method (IEnumerable<TSource>, Func<TSource, Int32, TResult>)
list = list.Cast<object>().Select( (v, i) => new {Value= v, Index = i});
foreach(var row in list)
{
bool IsChecked = (bool)((CheckBox)DataGridDetail.Columns[0].GetCellContent(row.Value)).IsChecked;
row.Index ...
}