Fully Integrated Electro-Optic Sensor for Real-Time MRI Guided Interventions - PROJECT SUMMARY/ABSTRACT Minimally invasive, image-guided interventions have been demonstrated to reduce mortality, morbidity, recovery times, and procedure-related risks. Consequently, they are increasingly replacing invasive surgical procedures in the treatment of major diseases, ranging from cardiovascular disease to cancer. Current practice widely uses X-ray fluoroscopy for image guidance. However, this technique suffers from poor soft tissue contrast, hampering its use in complex procedures that require precise tissue localization, such as myocardial biopsy. It also exposes the patient to ionizing radiation, raising health concerns, particularly for patients who require multiple procedures over time. Unlike X-ray fluoroscopy, magnetic resonance imaging (MRI) has recently become the gold standard for image-guided interventions due to its ability to provide excellent soft tissue contrast while using non-ionizing radiation. It also provides functional information, such as blood flow velocities, perfusion, and diffusion. However, there has been very limited success to date in harnessing the power of MRI for procedural guidance. This is due to the unavailability of interventional devices such as catheters and needles that are safe and visible under MRI. Passive devices have shown shortcomings due to their imaging artifacts and poor contrast. On the other hand, most active devices based on coil or dipole antennas to detect radiofrequency (RF) signals for device localization under MRI use long conductive transmission lines. These devices, however, suffer from RF-induced heating due to RF energy deposition into these conductors during MRI, creating a safety hazard; this issue gets exacerbated at high magnetic fields (e.g., 3 tesla (T)). Although several methods have been proposed to mitigate RF heating, none has resulted in a clinical-grade device achieving a signal-to-noise ratio (SNR) sufficient for real-time device tracking. To address these limitations, we need to break away from the conventional scheme of relaying signals on conductors. Here, we propose a disruptive approach combining the latest advancements in nanofabrication and optics to develop an innovative clinical-grade electro-optic sensor for real-time position tracking of devices with virtually zero RF-induced heating under MRI. The sensor core element is a miniature probe, in which a coil antenna coupled with an optical microresonator (OMR), detects and converts an RF signal into an optical signal. The ultra-high quality factor OMR enhances the detected RF signal. An optical fiber carries the resulting signal to a module outside the body for sensor integration with a clinical MRI scanner. Unlike existing approaches, our novel design approach greatly enhances SNR and enables routing on an optical fiber instead of a long conductive transmission line, eliminating RF-induced heating and electromagnetic interference. We will package our sensor onto a commercially available MRI-compatible catheter to validate its clinical utility in tissue-mimicking phantoms and ex vivo in swine via MR imaging experiments at 1.5T and 3T. Successful demonstration of our electro-optic sensor as an active MRI marker can transform the field of MRI-guided interventions by opening the door to safer, novel, more complex, more effective, radiation-free, and minimally invasive interventions in various clinical fields.
