Magnetic resonance imaging implications of metal-reinforced spinal microcatheters

STUDY OBJECTIVE: To estimate the magnitude behavior of ferrous-alloy, wire-reinforced microcatheters for subarachnoid anesthesia and the possible hazards of exposing patients to magnetic resonance imaging (MRI) after accidental catheter fracture within the subarachnoid space. DESIGN: Open, qualitative in vitro study. SETTING: MRI facility of a university-affiliated medical center. MEASUREMENTS AND MAIN RESULTS: Measurements were made of the angular deflection of 28-gauge and 32-gauge TFX catheters from their resting alignment by a small bar magnet. Mobility of 28-gauge catheter fragments 3.0 to 3.5 cm in length and 3.3 to 4.0 mg in mass were tested (1) when lying free on a polished surface in an MRI magnetic field of 1.5 tesla and 60 cm from the magnetic casing, and (2) when mounted on a mildly viscous agar surface 40 to 50 cm from the magnetic casing. Catheters were attracted to a small bar magnet and could be pulled out of alignment by the magnetic attraction to a degree inversely proportional to their caliber. Catheter fragments released in a magnetic field of 1.5 tesla flew from a glass surface and attached themselves firmly to the magnet casing, while catheter fragments adhering to an agar surface were not levitated but were rotated from their resting orientation. CONCLUSIONS: The microcatheters under test exhibited marked magnetic properties. Two questions arise: First, should MRI be avoided in patients where broken TFX catheter fragments may lie partly or completely within the subarachnoid space? Second, should ferrous metallic strengthening wire be replaced by a nonmetallic fiber of comparable or greater tensile strength? Further in vitro studies are indicated to answer these questions.