jQuery - Select first cell of a given row?

I have a table with images in one column. When I click the image, would like to get the text value of the first column in that row.

I can get the whole row with this:

var a = $(this).parents('tr').text();

However, I cannot isolate the first cell of the row.

I've tried

var a = $(this).parents('tr td:first').text();

But that just returns the first cell of the entire table.

Can anyone help me out?

Thanks.