A pilot study on an electromagnetic tracking system using tunneling magnetoresistance (TMR) sensors applicable to a 4F catheter (1.4 mm in diameter).

Purpose: Tracking the position and orientation of a 4F catheter ([Formula: see text] 1.4 mm) is required in superselective intra-arterial chemotherapy (SSIAC). Tunneling magnetoresistance (TMR) sensors, which measure magnetic fields, are promising candidates because the size of the TMR sensor can be less than a few tenths of a millimeter. The purpose of this paper is to prove the feasibility of an EMT system utilizing TMR sensors as magnetometers.

Methods: Three 1-axis TMR sensors (0.3 mm × 0.3 mm) were packaged on a flexible printed circuit board (PCB) together with an amplifier chip. The PCB was integrated into a 4F catheter. Six field generator coils driven by alternating current (AC) at different frequencies were used. Magnetic field measurement errors were evaluated to assess the effect of electromotive force (EMF) on TMR-based sensing by changing the coils' driving frequencies. The tracking error was also evaluated. As a result, the feasibility of catheter navigation utilizing the EMT system was demonstrated.

Results: There was a positive correlation between the frequency and the magnetic field measurement error using the TMR sensor (R = 0.999). With magnetic field frequencies less than 603 Hz, the average position and orientation estimation error were 10.1 mm and 2.3 degree, respectively. Under ideal conditions, the average estimation error values were 0.9 mm and 0.3 degree, respectively.

Conclusion: The position and orientation errors varied with frequency owing to the induced electromotive force. We should consider the effect of electromotive force on TMR sensor assemblies caused by alternating magnetic fields. An EMT system using TMR sensors was validated, although room for further improvement was identified.