Volume 20, Issue 4 p. 1049-1057

Mechanisms of signal loss in magnetic resonance imaging of stenoses

J. C. Gatenby

J. C. Gatenby

Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut

Department of Medical Engineering and Physics, King's College School of Medicine and Dentistry, London, United Kingdom

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T. R. McCauley

T. R. McCauley

Department of Diagnostic Radiology, Yale University, School of Medicine, New Haven, Connecticut 06510

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J. C. Gore

J. C. Gore

Department of Diagnostic Radiology, Yale University, School of Medicine, New Haven, Connecticut 06510

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First published: July 1993
Citations: 47

Abstract

Some of the factors affecting the signal losses that occur in magnetic resonance images at a stenosis or other region of complex flow have been evaluated. The important determinants of dephasing within a volume element are the net gradient moments, which can be kept small even at long echo times. For compact gradient wave forms, the echo time by itself is unimportant and does not affect signal losses. Reducing the fraction of echo sampled is an alternate method to velocity compensation for reducing gradient moment dephasing that keeps higher moments small. The effects of reducing the fraction of echo sampled on the signal losses in flow distal to a stenosis have been measured experimentally. Another source of signal loss at a stenosis is the variation of the mean phase within a volume element that occurs for flow that varies from one phase encoded view to another. Changes in flow behavior between acquisitions lead to signal displacement in the image. These view to view changes have also been quantified.