US 5,352,979 AGranted

Magnetic resonance imaging with contrast enhanced phase angle reconstruction

OwnerThomas E. Conturoinventor

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Abstract

The magnetic resonance image of a specimen is encoded by the phase angle response of the volume elements in a slice or volume illuminated by a pulsed radio frequency source, instead of encoded by the magnitude response. The specimen can be imaged before and during intrinsic perturbations such as caused by external stimuli or execution of cognitive or motor tasks. Preferably the specimen is perfused with a paramagnetic contrast agent such as Gadolinium or Dysprosium, slowly or by bolus injection, after recording one or more baseline images. The phase angle response of the specimen can then be recorded one or more times as perturbation subsists or as the bolus traverses the area of illumination. Fast Fourier transformation converts gradient spin echo response data to phase angles for a spatial distribution of volume elements in the illuminated slice. The baseline phase angle image is subtracted from the image taken after the bolus injection, providing a high contrast image showing the concentration of the contrast agent. The change .DELTA..phi. in phase angle between the images is proportional to the concentration of the contrast agent, enabling accurate measurements of localized blood volume and flow rate. The invention is particularly applicable to visualization of localized ischemia caused by cerebral vascular disease, such as stroke.

Claims35

Dependent claims

A method for imaging a specimen comprising one of a substance traversed by passages and a material having a changeable magnetization, comprising the steps of:

illuminating the specimen along at least one plane traversing the localized area, using a pulsed radio frequency source, and collecting at least one baseline sample representing an electromagnetic response of the specimen to the pulsed radio frequency source;
altering a magnetic property of the specimen by one of perfusing the specimen with an agent having a magnetic property different from a corresponding magnetic property of the specimen at least in a localized area to be imaged, and physically perturbing the specimen to induce a macroscopic change in the magnetic property;
illuminating the specimen along at least one plane traversing the localized area, using the pulsed radio frequency source;
collecting a plurality of data samples representing the electromagnetic response of the specimen, including the agent, to the pulsed radio frequency source;
converting the data samples into a map of phase information for an array of volume elements in said plane to thereby construct an image from variations in the electromagnetic responses of the volume elements as represented by different shifts in one of frequency, phase, real, imaginary and complex signal information between the source illuminating the specimen and the data samples collected therefrom:
correcting phase angles representing the volume elements in the array to cancel variations that are present in both the data samples and the baseline sample;
and,
identifying variations in the localized area by corresponding variations in phase information of the volume elements in said map.

5 more elements

An apparatus for magnetic resonance imaging, comprising:

a source of a pulsed radio frequency signal for illumination of a specimen along at least one plane traversing the specimen;
sampling means operable to acquire a plurality of data samples representing at least one of an electromagnetic gradient echo response and a spin echo response of the specimen to the pulsed radio frequency signal;
data processing means operable to store at least two sets of said data samples corresponding to successive responses of the specimen to the pulsed radio frequency signal, the data processing means including a Fourier transform means operable to convert the data samples to complex intensities, and the data processing means converting the complex intensities to a map of phase information representing a phase response of individual volume elements in the plane to the pulsed radio frequency signal through a macroscopic volume of the specimen, and means for correcting the phase response of the individual volume elements in a second of the two sets from a first of the two sets;
means for altering a magnetic property of the specimen in the macroscopic volume, between acquisition of the two sets;
and,
a display coupled to the data processing means for graphic representation of the phase response of the individual volume elements.

3 more elements

Dependencies are inferred from the claim text.