Real time magnetic field mapping using MRI
OwnerPaul R. Harveyinventor
Life of this patent
Estimating the term…
Abstract
A method is provided for evaluating an inhomogeneity in a magnetic polarizing field used to acquire an MRI image of a slice of a subject, at a point in the slice, the method comprising: acquiring data in a k-space for first and second k-space scans of the subject with a single application of a first MRI pulse sequence, wherein data acquisition for the second k-space scan is delayed with respect to data acquisition for the first k-space scan by a time delay; generating first and second spatial images from the first and second k-space scans; determining a phase difference between values of the first and second spatial images at the point; and evaluating the inhomogeneity at the point using the phase difference and the time delay.
Claims20
A method for measuring the inhomogeneity in a magnetic polarizing field at a point in a slice of a subject to which a magnetic polarizing field is applied to acquire an MRI image of a slice said method comprising:
- (1) acquiring data in a k-space for first and second k-space scans of said subject with a single application of a first MRI pulse sequence, wherein said MRI pulse sequence, comprises:
- (a) a train of alternating polarity read gradient pulses having substantially same magnitude and duration, wherein said slice is perpendicular to a z axis of a spatial coordinate system and said read gradient pulses provide magnetic field gradients in said slice in an x direction of said coordinate system;
- (b) a train of substantially identical phase gradient pulses that provide a magnetic field gradient in a y direction of said coordinate system and wherein a phase gradient pulse occurs after every other read gradient pulse in said train of read gradient pulses;
- and
- (c) wherein data acquisition for said second k-space scan is delayed with respect to data acquisition for said first k-space scan by a time delay;
- (2) generating first and second spatial images from said first and second k-space scans;
- (3) determining a phase difference between values of said first and second spatial images at said point;
- and
- (4) measuring said the inhomogeneity at said point using said phase difference and said time delay.
A method for providing real time measurements of changes in blood oxygenation at points in a slice of living tissue comprising:
- (1) applying a polarizing magnetic field to said slice;
- (2) measuring changes in the magnetic field at said points in said slice using a method for providing a substantially real time measurement of a change in a magnetic field at a point in a slice of a subject positioned in a polarizing magnetic field, said method comprising:
- (a) measuring an inhomogeneity in said polarizing magnetic field at said point at a first time to acquire a first measurement of said inhomogeneity by:
- (I) acquiring data in a k-space for first and second k-space scans of said subject with a a single application of a first MRI pulse sequence, comprising:
- (a) a train of alternating polarity read gradient pulses having substantially same magnitude and duration, wherein said slice is perpendicular to a z axis of a spatial coordinate system and said read gradient pulses provide magnetic field gradients in said slice in an x direction of said coordinate system;
- (b) a train of substantially identical phase gradient pulses that provide a magnetic field gradient in a y direction of said coordinate system and wherein a phase gradient pulse occurs after every other read gradient pulse in said train of read gradient pulses;
- and
- (c) wherein data acquisition for said second k-space scan is delayed with respect to data acquisition for said first k-space scan by a time delay;
- (II) generating first and second spatial images from said first and second k-space scans;
- (III) determining a phase difference between values of said first and second spatial images at said point;
- and
- (IV) measuring said inhomogeneity at said point using said phase difference and said time delay;
- wherein data acquisition for said second k-space scan is delayed with respect to data acquisition for said first k-space scan by a time delay;
- (B) repeating said measurement at a second time following a short delay to acquire a second measurement of said inhomogeneity;
- and
- (C) providing a measurement of said change by determining a difference between said first and second measurements;
- and
- (3) correlating said changes with changes in magnetic susceptibility of blood to determine changes in blood oxygenation at said points.
A method for providing a substantially real time measurement of a change in a magnetic field at a point in a slice of a subject positioned in a polarizing magnetic field, said method comprising:
- (1) measuring an inhomogeneity in said polarizing magnetic field at said point at a first time to acquire a first measurement of said inhomogeneity by:
- (I) acquiring data in a k-space for first and second k-space scans of said subject with a single application of a first MRI pulse sequence, comprising:
- (a) a train of alternating polarity read gradient pulses having substantially same magnitude and duration, wherein said slice is perpendicular to a z axis of a spatial coordinate system and said read gradient pulses provide magnetic field gradients in said slice in an x direction of said coordinate system;
- (b) a train of substantially identical phase gradient pulses that provide a magnetic field gradient in a y direction of said coordinate system and wherein a phase gradient pulse occurs after every other read gradient pulse in said train of read gradient pulses;
- and
- (c) wherein data acquisition for said second k-space scan is delayed with respect to data acquisition for said first k-space scan by a time delay;
- (II) generating first and second spatial images from- said first and second k-space scans;
- (III) determining a phase difference between values of said first and second spatial images at said point;
- and
- (IV) measuring said inhomogeneity at said point using said phase difference and said time delay;
- (2) repeating said measurement at a second time following a short delay to acquire a second measurement of said inhomogeneity;
- and
- (3) providing a measurement of said change by determining a difference between said first and second measurements.
Dependencies are inferred from the claim text.