A puncturing needle holder is attached to a flat-panel x-ray detector such that it is visible in the x-ray image as a point. In another embodiment, there is shown a method of conducting heat away from an electronic device wherein the electronic device is constructed on a circuit board, the method comprises placing a plurality of heat transfer devices in heat transfer relationship with the electronic device and passing air through the heat transfer devices in at least one air flow direction. The second sectional part has a smaller area than that of the first sectional part and defined by fourth to sixth sides.