NMR rheotomography: feasibility and clinical potential.
An investigation has been undertaken of the effect of flow on NMR images. We term the new technique of flow analysis examined here, NMR rheotomography. Images were acquired through use of a spin-echo technique. They were of doped water passing through a glass U-tube, simulating a small vein, which fitted into the magnetic field gradient and radiofrequency coils of an NMR imaging apparatus. For the case of the inlet arm of the U-tube, the flow images displayed an intensity distribution which compared favorably to a simple physical model based on laminar flow. The intensity distribution observed for the outlet arm was explained through consideration of the perturbation to flow introduced by the U-bend. Generally, the results of the feasibility study indicate that (a) the NMR spin-echo image is modified by flow in a predictable manner, (b) display of the velocity profile is possible, (c) through use of a U-tube some separation can be demonstrated within a single image of the twin factors, proton incursion into the image "slice" and proton dephasing, which generally combine to modify the flow image intensity, and (d) discrimination between different modes of flow may be possible by NMR CT. The clinical potential suggested by the results is discussed; NMR rheotomography may prove to be particularly useful for the noninvasive diagnosis of structurally-originating cardiovascular defects.
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