A medical catheter comprising a proximal end having an opening for fluid containing a therapeutic drug, a distal end, the distal end defining at least one opening, and a porous portion covering the opening defined by the distal end. A housing contains a plurality of lancets and optionally includes test elements to take up a sample of blood, an evaluation system and a display. The beam-deflecting field thus produced is stable with respect to temperature changes, is little affected by eddy currents, and exhibits low aberration caused by manufacturing tolerances of the coil and core. In an alternative embodiment, the wale is of a unitary construction and the plurality of connecting walls includes atop, upper reinforcing, lower reinforcing, and bottom walls, which form a plurality of chambers between the back and front walls. An extended layer decoding section normally decodes the extended layer coded data.