ORIGINAL RESEARCH PATIENT SAFETY Endovascular Catheter forMagnetic Navigation underMR Imaging Guidance: Evaluation of Safety In Vivo at 1.5T

BACKGROUNDANDPURPOSE: Endovascular navigationunderMR imaging guidance canbe facilitatedby a catheterwith steerablemicrocoils on the tip. Not only do microcoils create visible artifacts allowing catheter tracking, but also they create a small magnetic moment permitting remote-controlled catheter tip deflection. A side product of catheter tip electrical currents, however, is the heat that might damage blood vessels. We sought to determine the upper boundary of electrical currents safely usable at 1.5T in a coil-tipped microcatheter system. MATERIALSANDMETHODS: Alumina tubeswith solenoid copper coilswere attached toneurovascularmicrocatheterswithheat shrink-wrap. Catheters were tested in carotid arteries of 8 pigs. The catheters were advanced under x-ray fluoroscopy andMR imaging. Currents from 0mA to 700 mAwere applied to test heating and potential vascular damage. Postmortem histologic analysis was the primary endpoint. RESULTS: Several heat-mitigation strategies demonstrated negligible vascular damage compared with control arteries. Coil currents 300 mA resulted in no damage (0/58 samples) compared with 9 (25%) of 36 samples for 300-mA activations (P .0001). Tip coil activation 1 minute and a proximal carotid guide catheter saline drip 2 mL/minute also had a nonsignificantly lower likelihood of vascular damage. For catheter tip coil activations300 mA for1 minute in normal carotid flow, 0 of 43 samples had tissue damage. CONCLUSIONS: Activations of copper coils at the tip of microcatheters at low currents in 1.5T MR scanners can be achieved without significant damage to blood vessel walls in a controlled experimental setting. Further optimization of catheter design and procedure protocols is necessary for safe remote control magnetic catheter guidance