One embodiment having features of the invention is directed to a guide block for an MRI device which has a block body with a proximal face, a distal face, and four parallel passageways extending between the two faces. The first passageway is centrally disposed, the second passageway is disposed vertical or horizontal to the first, the third passageway is located diagonal to the first and has a longitudinal opening in fluid communication with the first passageway, and the fourth passageway is diagonal to the first and in an opposite side of the body from the third passageway. In an alternative embodiment the guide block has at least one passageway that is not parallel to the longitudinal axis.