Nuclear magnetic resonance blood flowmeter

Abstract

Blood flow in human limbs is measured non-invasively by a nuclear magnetic resonance blood flowmeter which includes a pair of polarizing magnets whose fields are stabilized by electromagnets in each pole piece that are energized in accordance with the magnetic flux of the magnets as sensed by a Hall effect sensor. Blood molecules are either self-tagged by the polarizing field or are separately tagged by a tag coil whose field is orthogonal to the polarizing field. Once tagged, the variation in the magnetic moment of the molecule due to the tagging is detected by the variation in voltage in the receiver coil which is located orthogonally to the transmitter coil so as to reduce crosscoupling therebetween. Two sets of scanner coils, one located parallel to and the other orthogonal to the polarizing field directions, respectively, are energized to create a pair of intersecting null planes which act to cancel nuclear magnetic resonance response detected by the receiver everywhere but along the line where the two null planes intersect. By varying the current in the scanner coils, the resulting line of intersection of the null planes can be moved in two dimensions so as to scan the limb thereby allowing blood flow measurement at various locations within the limb.