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The purpose of this study is to describe a new active technique for accurately determining both the position and orientation of the tip of a catheter during magnetic resonance (MR)-guided percutaneous cardiovascular procedures. The technique utilizes phase information introduced into the MR signal from a small receive coil located on the distal tip of the catheter. Phase patterns around a small receive coil are rich in information that is directly related to position and orientation. This information can be collected over a large spherical volume with a diameter several times that of the receive coil. The high degree of redundancy yields the potential for an accurate and robust method of catheter tracking. A tracking algorithm is presented that performs catheter tip localization using phase images acquired in two orthogonal planes without any a priori knowledge of catheter position. Associated experimentation demonstrating feasibility is also presented. [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging (MRI) pulse sequence consoles typically employ closed proprietary hardware, software, and interfaces, making difficult any adaptation for innovative experimental technology. Yet MRI systems research is trending to higher channel count receivers, transmitters, gradient/shims, and unique interfaces for interventional applications. Customized console designs are now feasible for researchers with modern electronic components, but high data rates, synchronization, scalability, and cost present important challenges. Implementing large multichannel MR systems with efficiency and flexibility requires a scalable modular architecture. With Medusa, we propose an open system architecture using the universal serial bus (USB) for scalability, combined with distributed processing and buffering to address the high data rates and strict synchronization required by multichannel MRI. Medusa uses a modular design concept based on digital synthesizer, receiver, and gradient blocks, in conjunction with fast programmable logic for sampling and synchronization. Medusa is a form of synthetic instrument, being reconfigurable for a variety of medical/scientific instrumentation needs. The Medusa distributed architecture, scalability, and data bandwidth limits are presented, and its flexibility is demonstrated in a variety of novel MRI applications. [ABSTRACT FROM PUBLISHER]

The currents induced in long conductors such as guidewires by the radio-frequency (RF) field in magnetic resonance imaging (MRI) are responsible for potentially dangerous heating of surrounding media, such as tissue. This paper presents an optically coupled system with the potential to quantitatively measure the RF currents induced on these conductors. The system uses a self shielded toroid transducer and active circuitry to modulate a high speed light-emitting-diode transmitter. Plastic fiber guides the light to a photodiode receiver and transimpedance amplifier. System validation included a series of experiments with bare wires that compared wire tip heating by fluoroptic thermometers with the RF current sensor response. Validations were performed on a custom whole body 64 MHz birdcage test platform and on a 1.5 T MRI scanner. With this system, a variety of phenomena were demonstrated including cable trap current attenuation, lossy dielectric Q-spoiling and even transverse electromagnetic wave node patterns. This system should find applications in studies of MRI RF safety for interventional devices such as pacemaker leads, and guidewires. In particular, variations of this device could potentially act as a realtime safety monitor during MRI guided interventions. [ABSTRACT FROM AUTHOR]

Prepolarized MRI uses pulsed magnetic fields to produce MR images by polarizing the sample at one field strength (∼0.5 T) before imaging at a much lower field (∼50 mT). Contrast reflecting the T1 of the sample at an intermediate field strength is achieved by polarizing the sample and then allowing the magnetization to decay at a chosen 'evolution' field before imaging. For tissues whose T1 varies with field strength ( T1 dispersion), the difference between two images collected with different evolution fields yields an image with contrast reflecting the slope of the T1 dispersion curve between those fields. Tissues with high protein content, such as muscle, exhibit rapid changes in their T1 dispersion curves at 49 and 65 mT due to cross-relaxation with nitrogen nuclei in protein backbones. Tissues without protein, such as fat, have fairly constant T1 over this range; subtracting images with two different evolution fields eliminates signal from flat T1 dispersion species. T1 dispersion protein-content images of the human wrist and foot are presented, showing clear differentiation between muscle and fat. This technique may prove useful for delineating regions of muscle tissue in the extremities of patients with diseases affecting muscle viability, such as diabetic neuropathy, and for visualizing the protein content of tissues in vivo. Magn Reson Med 2006. © 2006 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

OBJECTIVES: A dynamic real-time(dRT) architecture has been developed to address limitations in magnetic resonance coronary angiography(MRCA). A prospective clinical trial of 45 patients suspected of coronary artery disease was conducted to determine clinical utility of this integrated real-time system. BACKGROUND: Clinical implementation of MRCA is not performed routinely today. However, improved anatomic coverage, image quality, and scan flexibility may enhance its clinical utility. A novel real-time architecture addresses these challenges through instantaneous reconfiguration between real-time(RT) and high-resolution(HR) imaging sequences with dynamic selection of the desired element on a custom-designed receiver coil. METHODS: A total of 45 subjects were recruited consecutively to evaluate scan time, anatomic coverage, image quality, and detection of coronary lesions. Using a modern PC, the dRT switches from RT to gated HR imaging sequence in one repetition time(39 ms). Magnetic resonance imaging(MRI) scanning was performed using a custom-designed coronary coil consisting of two four-inch phase-array circular elements enabled with real-time selection of the desired coil element. RESULTS: All studies were completed in less than 45 minutes and required a mean of 12 breath holds(16 heartbeats). Of the total number of coronary segments, 91%(357/394) were visualized. Excellent or good image quality was achieved in 86% of the segments. Blinded analysis of the coronary arteries revealed sensitivity of 93% and specificity of 88% in the detection of coronary stenoses. CONCLUSIONS: The integrated environment of dRT provides a rapid and flexible scan protocol for MRCA while achieving wide anatomical coverage, high image quality, and reliable detection of coronary stenosis in short scan time. [ABSTRACT FROM AUTHOR]