Minimally invasive image-guided interventions such as balloon angioplasty, stent placement, and coiling of aneurysms, provide reduced mortality, morbidity, and recovery times. Consequently they are increasingly and rapidly replacing invasive surgical procedures in the treatment of patients suffering from vascular disease. In the endovascular image-guided interventions, MRI is advantageous over other commonly-used imaging modalities (e.g., x-ray and CT) due to its non-ionizing radiation characteristic and its ability to provide soft tissue contrast, tissue chemical composition, and functional information, including blood flow velocities, perfusion and diffusion, and tissue metabolomics. In interventional procedures, it is critically important to accurately and rapidly detect the actual location of the endovascular devices or catheters and also the site of the pathology to be treated. In contrast to global detection in which the MR body coil is used for visualizing the catheter, local detection using an RF coil mounted on the tip of the endovascular catheter provides high sensitivity, allowing accelerated imaging and more accurate catheter localization. The increased sensitivity of the catheter coils is also critical in obtaining the required high spaial resolution. In current catheter coil designs, the coil's long and 'hot' leads exposed to surroundin tissues significantly increase the coil losses, leading to degraded detection sensitivity. They als create a safety hazard because of augmented RF energy deposition or specific absorption rate (SAR) along the leads during RF transmit, resulting in locally elevated temperatures in adjacent tissue. With increased operation frequency, these problems are more pronounced at high magnetic fields (e.g., 3T). In addition, the requirement of lumped capacitors in RF coils makes it challenging to incorporate such bulky structures into miniature endovascular devices. In fact, the lack of efficient and practical catheter RF coils has become a major hindrance for further development and clinical translation of endovascular image-guided interventions. In this project, we propose to develop whole new catheter RF coils at the high field of 3T using the recently introduced transmission line resonator (TLR) RF coil technology. The proposed TLR catheter coils are characterized by high detection sensitivity, reduced E-fields/SAR along the immersed catheter, and compact physical size. The major goals of this project are: 1) design and construction of new types of catheter RF coils at 3T using the TLR technology, 2) establishment of numerical models to understand the TLR catheter coils with and without load in resonant frequency, B1-field efficiency, imaging coverage, E-field distribution, and SAR/safety, and 3) validation of proposed catheter coil technology via MR imaging experiments and performance comparison with existing lumped-element catheter coils and safety assessment in vitro and in vivo. Successful outcome of this project would result in significant advances in catheter engineering that are critical to the future success of MRI guided clinical endovascular interventions.
Stroke or neurovascular disease, cancer, and cardiovascular disease are the major causes of death and disability in the United States, and MRI plays an important role in the diagnosis and evaluation of these disorders. The technology to be developed in this project provides an efficient imaging technique with highly sensitive yet safer imaging acquisition for endovascular interventional MRI. This could ultimately lead to safer, more efficacious and practical diagnosis strategies for several major causes of morbidity and mortality.
