A novel two-element, catheter-based phased array coil was designed and built for both active MR device tracking and high-resolution vessel wall imaging. The device consists of two independent solenoid coils that are wound in opposite directions, connected to separate receive channels, and mounted collinearly on an angiographic catheter. The elements were used independently or together for tracking or imaging applications, respectively. The array's dual functionality was tested on a clinical 1.5 T MRI scanner in vitro, in vivo, and in situ. Key words: intravascular MRI; catheter RF coils; vessel wall imaging; interventional device tracking; phased arrayThe ultimate goal of endovascular MRI-guided interventions is to combine MRI's diagnostic capabilities (e.g., angiography, morphology, plaque analysis, and perfusion imaging) with therapeutic interventions such as angioplasty, atherectomy, and stent placement. A succesful MRI-guided endovascular therapeutic procedure incorporates the following critical steps: MR guidance of the interventional device to the target region, high-resolution imaging at the target location in order to diagnose disease within the vessel wall, performance of a therapeutic intervention, and evaluation of the efficacy of therapy. Integrated multifunctional devices are necessary to meet these demands, and are the subject of recent research (e.g., Ref.

This work demonstrates the feasibility of using wireless, tuned fiducial markers with a limited projection reconstruction-fast imaging with steady-state free precession sequence (LPR-FISP) to accurately obtain tracking information necessary for interactive scan plane selection in magnetic resonance imaging (MRI). The position and orientation of a rigid interventional device can be uniquely determined from the 3D coordinates of three fiducial markers mounted in a known configuration on the device. Three fiducial markers were tuned to the proton resonant frequency in a 0.2T open MR scanner and mounted to the surface of a cylindrical water phantom. An LPR-FISP sequence was developed to suppress the water phantom signal while preserving that of the fiducial markers through a nonselective low-tip-angle excitation and a dephaser gradient applied prior to data acquisition. A localization algorithm was developed to accurately calculate the 3D coordinates of the fiducial markers using four LPR-FISP projections in two orthogonal scan planes. Index terms: interventional MRI; active tracking; fiducial markers; projection reconstruction; radial FISP; device localization MAGNETIC RESONANCE (MR)-GUIDED DEVICE tracking has become an important research area for development of new MR technology that will provide a variety of important capabilities in the future. One key component of current tracking methods is the ability to automatically define an appropriate MR imaging (MRI) scan plane. This feature reduces the time and patient risk associated with interventional procedures. Frameless stereotactic systems have been developed to provide interactive scan plane selection by measuring the position of fiducial markers or light emitting devices (LEDs) mounted onto the surface of a rigid interventional device (1-4). The navigational wands are considered to be less cumbersome than conventional reference frames and articulation arms (5,6). However, optical frameless stereotactic tracking systems have been criticized because they suffer from a number of important limitations. First, they require a line of sight between the markers and the detection system. Second, this requirement hinders positioning of the detection systems within the scan room, which in turn restricts the range of motion of the physician during the procedure. Third, these stereotactic detection systems also add additional (and potentially expensive) components to an already congested physical environment. And finally, they require calibration between the tracking system and the MRI coordinate frames.In this work, a new tracking method is proposed that combines wireless tuned fiducial markers, a limited projection reconstruction-fast imaging with steadystate precession pulse sequence (LPR-FISP), and a marker localization algorithm. Device tracking and interactive scan plane selection is possible by determining the 3D coordinates of the fiducial markers when a minimum of three fiducial markers are mounted onto a rigid interventional device (e.g., biopsy needle). The syst...

Purpose:To evaluate the performance of a real-time MR system for interventional procedures that adjusts specific image parameters in real time based on a catheter's speed of insertion. Materials and Methods:The system was implemented using only the hardware provided with a standard short-bore 1.5 T scanner (Siemens Magnetom Sonata) (with the exception of small tracking markers affixed to the catheter). The system tracks the position of an MR microcoil-instrumented catheter and automatically updates the scan plane's position and orientation, as well as other features, including, but not limited to, field of view, resolution, tip angle, and TE. A realtime feedback loop continuously localizes the tracking markers, updates the scan plane position and orientation, calculates the catheter's speed, adjusts the value of specific image parameters, then collects new image data, reconstructs an image, and provides it for immediate display. The system was evaluated in phantom and in vivo porcine experiments. Results:The system is able to accurately localize a moving catheter in the abdominal aorta, calculate the device speed, and respond by adjusting specified image parameters 98% of the time, with precision of approximately 2 mm and 1.5°. Conclusion:Simply slowing the speed of the catheter allows the clinician to adjust predetermined image parameters. This work also has the potential to build a degree of intelligence into the scanner, enabling it to react to changes in the clinical environment and automatically optimize specific image parameters.