The present invention relates to A device for measurements, insertable into a living body, comprising an elongated flexible member (2, 30) with a proximal end and a distal end and a central lumen with an inner wall. The lumen is filled with a core (22) and an insulating material (21) is provided between the core and the inner wall; the core (22) is made of an electrically conductive material and has an essentially constant diameter over its entire length. An electrical sensor (44) is attached to the distal end of the elongated flexible member and is electrically connected (52) to the core (22).