Methods for measuring perfusion using magnetic resonance imaging

Abstract

Methods for measuring the perfusion of fluid in a substance are shown to include subjecting the fluid to electromagnetic energy so as to cause a response related to the magnetization of the fluid before it enters the substance, performing magnetic resonance measurements on the substance to generate intensity information and processing the intensity information to determine perfusion. In one embodiment of the invention, perfusion is measured by labeling atoms in the fluid at a base point, generating a steady state in the substance by continuing to label atoms until the effect caused by labeled atoms perfusing in the substance, reaches a steady state, generating image information for the substance and processing the image information to determine perfusion. It is preferred to label atoms by applying magnetic resonance perturbation. In one embodiment the labeling of atoms involves saturating spins associated with the atoms. In an especially preferred embodiment labeling involves inverting spins associated with the atoms continuously by adiabatic fast passage. Such inversion is preferably achieved by applying a radio frequency field virtually continuously. The invention is particularly useful where the substance is tissue and wherein the fluid is blood. In such an embodiment, labeling involves labeling the hydrogen atoms of water contained in the blood. It is also preferred for labeling to occur at a point between the heart and the tissue. It is also especially preferred for the generation of magnetic resonance images to involve generating a first image while labeling at the base point, labeling at a remote point, generating a second image while labeling at the remote point and generating a relaxation image. In such an embodiment, all of the images are processed in the determination of perfusion.