With recent improvements in both hardware (gradients, receiver hardware, etc.) and software (fast imaging sequences), magnetic resonance imaging (MRI) has evolved from a purely diagnostic role to one that includes therapy. Minimally invasive image guided therapy requires a quick and robust method for localization and tracking of interventional devices inserted into the body. To this end, active tracking applications have been proposed as a means to facilitate this guidance. The purpose of my research project in this field is to design a tracking coil that incorporates an internal signal source while retaining minimal dimensions and localization abilities when advanced in a vessel through various orientations.
Tracking coil devices with both single and double active loop elements have been constructed and mounted on 5-French catheters. Active loop elements were wound from 30 AWG copper magnet wire. Dimensions of the loop elements are approximately 4 mm along the long axis and 2.5 mm along the short axis. For the double loop device, loops were wound with a center-to-center distance of 23mm. Tuning and matching of the resonant circuit was accomplished using surface mount capacitors. Capacitive coupling to the MR receiver system was made utilizing a micro-coaxial cable. A plastic tube was then affixed over the active antenna elements and secured into place with epoxy. The tube was then filled with an internal signal source and sealed. The final device measures 11 F in diameter. A picture of the single active loop device is shown.
Experiments were successful in isolating and following the active antenna elements of the tracking system. Catheter advancement and retraction were successfully tracked in all imaging experiments. The contrast to noise ratio (CNR) of the internal signal source was approximately 10 during the tracking phase of the experiments. System accuracy was found to be better than 3mm in displacement error and 2 degrees orientation error.
This catheter-based, active system with an internal signal source for device tracking has been constructed and been shown to provide quick, accurate and robust in-vivo localization and tracking. Further work will be performed to enhance antenna design and reduce overall package size.
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