Catheter based minimally invasive interventions are becoming a preferred method as compared to surgical procedures due to the reduction of operation time, patient discomfort, hospitalization time, and procedure related risks. While X-ray fluoroscopy is widely used as a imaging guidance for the minimally invasive procedures such as treatment of obstructive coronary artery disease, peripheral artery atherosclerosis and aneurysm, and structural or congenital heart disease, magnetic resonance imaging (MRI) can provide superior soft tissue contrast while eliminating the ionization radiation exposure on both patient and operator in these procedures. MRI also provides multi slice imaging and allows physiological measurements such as blood flow, temperature, perfusion and motion. A significant issue with MRI guided interventions is that most traditional interventional devices (catheters, guidewires etc.) either invisible or not suitable for use under MRI. Active receive-onl devices using small coils or dipole antennae on the catheter shaft to detect the RF signals for device location and/or orientation under MRI use long conductive transmission lines. These approaches are problematic as RF induced heating over long conductor components of the devices needs to be addressed before moving on clinical trials. Although promising improvements in terms of RF induced heating problem have been achieved by detuning, RF chokes or transformers, none of these techniques can offer active device design that can have clinically acceptable mechanical performance. In this application, we aim to develop a clinical-grade active catheter device that does not need long conductor transmission lines for active device visualization under MRI. The active catheter design incorporates a distal loop coil that is electrically connected to an ultrasonic transducer having a comparable profile. This ultrasonic transducer induces ultrasonic waves at the Larmor frequency at the distal end of a dielectric optical fiber that runs along the active catheter shaft. This optical fiber serves as the transmission line instead of a conductor, eliminating the RF induced heating. The strain generated by the ultrasound transducer will be measured using optical interferometry by coupling a laser at the proximal end of the optical fiber using the acousto-optical effect. A fiber embedded Bragg reflector grating will be used for this purpose. The active devices will be designed, fabricated and incorporated into clinical grade catheter prototypes. The prototypes will be tested under MRI: in-vitro using specially prepared phantoms and in-vivo in large animals at NHLBI facilities.
Integration of an ultrasound to optical converter at the tip of a magnetic resonance imaging catheter and its successful demonstration as an active receiver with a non-conducting transmission line will be a significant step in achieving the goal of fundamentally more effective, more efficient, safer, novel, and radiation-free interventional procedures.