Given the clinical utility that has already been exhibited by our current implementation of the multiple overlapping thin slab acquisition technique (MOTSA) and the great flexibility inherent in the MOTSA technique, a systematic quantitative investigation of image quality and vessel visibility as a function of MOTSA imaging parameters will facilitate an improvement in spatial resolution as well as in the ability to visualize vessels with both slow flow and disordered flow. In this project we will develop techniques to substantially improve the vessel detail and absolute flow measurements obtainable with magnetic resonance angiography (MRA). We will improve the MOTSA technique to the point where arterial vessels on the order of 0.3 to 0.5 mm in diameter will be routinely visualized throughout a diagnostically useful 3D region (60 mm minimum dimension) in a reasonable examination time (less than 40 minutes). This resolution represents a significant improvement over the 0.6 mm voxel dimensions currently obtained in a 12 to 15 minute scan over the same region. By attaining a resolution of 0.3 mm we will have accomplished one of the most important steps toward the replacement of x-ray angiography with MRA. We will accomplish this goal of improved vessel resolution by performing a systematic (theoretical and experimental) evaluation of vascular detail as a function of vessel dimensions, orientation and flow states and the various imaging parameters which can be varied in MOTSA angiography. We will also demonstrate that quantitative volume flow measurements can be obtained from a second echo of MOTSA. This second MOTSA echo is available with no (or very little) increased in total scan time. We will test the following physical hypotheses: I. The improvements in spatial resolution that can be obtained by optimization of MOTSA technique factors will (A) result in improved visualization [Contrast to Noise Ratio, CNR] of small vessels in both phantom and human MR angiograms and (B) still allow visualization [in spite of decreased CNR] of large vessels. II. Hybrid velocity measurements, which are unique to the MOTSA technique, will provide quantitative flow measurements, complementing the diagnostic information available from vascular anatomy. With the improved small vessel CNR we will test the following clinical hypothesis: III. This improved small vessel CNR will result in enhanced visualization of arterial feeders to intracranial tumors. With these improvements in vessel visibility, this study will result in improved clinical utility and therefore be of significant importance to the field of MRA. Specifically, the proposed research will develop methods to improve resolution while retaining a sufficiently large field of view and a moderate imaging time. This project will solve the most important problem currently preventing MRA from replacing x-ray angiography. Successful completion of the project will lead to less invasive, safer and more cost effective methods of diagnosing vascular disease in humans.
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