Magnetic resonance imaging implications of metal-reinforced spinal microcatheters

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.

Open, qualitative in vitro study.

MRI facility of a university-affiliated medical center.

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.

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.