Tracking of MRI interventional devices with computer-controlled detunable markers

Accurate localization and fast tracking of interventional tools is an area of paramount importance in procedures with real-time MR guidance. Optically detunable radiofrequency (RF) coils are a robust method for the identification of individual MR markers for MR-compatible robotics system. In this study, we describe a technique for localizing and tracking four RF coils. Each coil consists of a 3 mm diameter inductively coupled solenoid coil with a photoresistor that is optically tuned and detuned. In particular, by selecting only one marker to be MR visible per data collection repetition, this particular marker point of the manipulator is unambiguously distinguished. This technique allows simplification of both the data acquisition and the post processing algorithms. A userprogrammable microcontroller times the ON/OFF state of light sources and triggers the MR scanner so that a particular image collection depicts a specific RF coil or combination. Phantom studies at 1.5T demonstrated the technique illustrating the selective observation of one or multiple markers. The described technique can use imaging to track multiple points on an interventional device, such as the shaft of steerable catheters and the end-effectors of MR-compatible manipulators.