Polyurethane catheter with NaCl or morphine sulfate infusion and magnetic resonance imaging (MRI). Representative hematoxylin and eosin–stained sections taken at the lumbar level, proximal to the catheter tip, from animals with polyurethane catheters and receiving infusions of saline for 14 days (A) or morphine sulfate (25mg/ml at 0.5μl/h) (B). All animals were harvested 16 days after catheter placement. For each animal, a postmortem MRI was taken to identify the catheter site and local reaction. *Catheter site.