One embodiment having features of the invention is directed to a guide block(10,52) for an MRI device which has a block body (12,54) with a proximal face(14,56) , a distal face (16,58) , and four parallel passageways (22,24,26,28)extending between the two faces. The first passageway (22) is centrallydisposed, the second passageway (24) is disposed vertical or horizontal to thefirst, the third passageway (26) is located diagonal to the first and has alongitudinal opening in fluid communication with the first passageway, and thefourth passageway (28) is diagonal to the first and in an opposite side of thebody from the third passageway. In an alternative embodiment the guide blockhas at least one passageway (62) that is not parallel to the longitudinal axis.
