MR FLUOROSCOPY TRIGGERING FOR HIGH RESOLUTION MRA

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DESCRIPTION (Adapted from Applicant's Abstract): The investigators propose to apply magnetic resonance imaging (MRI) techniques developed in the previous funding cycle of this grant to MR angiography imaging. The specific hypothesis to be tested is that high resolution arterial phase angiograms devoid of motion artifact can be reliably acquired in major vascular regions (renal, carotid, aorta, pulmonary) using intravenous contrast administration. Despite growing interest, 3-D contrast enhanced MR angiography is limited by major physical phenomena including: Uncertainties of timing, contamination by unwanted venous signal, limited spatial resolution, and, in the thoracic and abdominal regions, motion artifact. These all affect the overall reliability. The investigators propose to combine two methods to deal with these problems: (I) an elliptical centric view order, and (ii) real-time MR fluoroscopy. With the end product an operator will monitor the targeted vascular area with real-time MR Fluoroscopy and upon detection of contrast material immediately trigger a 3-D scan with a view order optimum for high resolution arterial phase imaging. Specific projects to be studied are: 1. Elliptical Centric 3DFT MR Acquisition. The fundamental ability of the elliptical view order to distinguish arterial and venous phases will be assessed theoretically and experimentally using hypothetical and measured contrast enhancement curves. TR times will be reduced to provide improved resolution; 2. MR Fluoroscopic Triggering. Imaging sequences and hardware will be developed for real-time monitoring of contrast material proximal to the targeted vasculature for the high resolution 3DFT sequence. Means will be developed for instantaneous initiation of the 3-D scan. Partial k-space updating with nonuniform sampling will be implemented for improved temporal resolution. Means will be studied to facilitate positioning of the fluoroscopic plane of section; and 3. System integration and adaptation to targeted vascular areas. The basic technique will be adapted to specific anatomic areas. Physical parameters to be accounted for include fast contrast passage (especially in pulmonary imaging), fine resolution in all three dimensions (carotid, renal), extended field of view (pulmonary, aorta) and multiple temporal frames (renal).