Potential heating caused by intraparenchymal intracranial pressure transducers in a 3-tesla magnetic resonance imaging system using a body radiofrequency resonator: assessment of the Codman MicroSensor Transducer

Magnetic resonance imaging and spectroscopy may provide important clinical information in the acute stages of brain injury. For this to occur it must be ensured that intracranial pressure (ICP) monitoring devices are safe to bring into the MR imaging suite. The authors tested a Codman MicroSensor ICP Transducer (Codman & Shurtleff, Inc.) within a 3-T MR imaging system using the transmit body coil and receive-only coils and the transmit-and-receive head coil. Extreme and rapid heating of 64 degrees C was noted with the transducer wire in certain positions when using the transmit body coil and receive-only head coil. This is consistent with the phenomenon of resonance, and the probe was shown to have a distinct resonant response when coupled to HP 4195A Network Analyzer (Hewlett Packard). Coiling some of the transducer wire outside of the receive-only head coil reduced the generated current and so stopped the thermogenesis. This may be due to the introduction of a radiofrequency choke. The ICP transducer performed within clinically acceptable limits in both the static magnetic field and during imaging with high radiofrequency power when the excess wire was in this configuration. No heating was observed when a transmit-and-receive head coil was used. This study has shown when using a high-field magnet, the Codman ICP probe is MR conditional. That is, in the authors' system, it can be safely used with the transi-nit-and-receive head coil, but when using the transmit body coil the transducer wire must be coiled into concentric loops outside of the receive-only head coil.