NMR imaging of blood flow by moment variation of magnetic gradients

• US 4,718,424 A
• Filed: 08/07/1986
• Issued: 01/12/1988
• Est. Priority Date: 08/07/1986
• Status: Expired due to Fees

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Stanford University
• Inventors: Nishimura, Dwight G.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Smith, Ruth S.
• Application Number:
  US06/894,318
• Time in Patent Office: 523 Days
• Field of Search: 128/653, 324/306, 324/309
• US Class Current: 600/419
• CPC Class Codes: G01R 33/56308 Characterization of motion or flow; Dynamic imaging
• CPC Class Codes: G01R 33/56316 involving phase contrast techniques

Abstract

Selective material projection imaging in which static and flowing material are distinguishable utilizes magnetic gradients whose waveforms have selective moments. The effects of the magnetic field gradients are utilized in obtaining data for a plurality of images whereby the subtraction of image data will result in selected material imaging. The zero moment of a magnetic gradient waveform affects the phase of static material and the phase of moving material, while the first moment of a magnetic gradient waveform affects the phase of constant velocity moving material but not the phase of static material. The second moment of a magnetic gradient waveform affects the phase of varying velocity moving material but not the phase of static material or constant velocity material. The nuclear spins of a region of a body can be excited under different conditions of an applied magnetic field gradient so that data under the different conditions can be subtracted to eliminate selected material. Alternatively, the two magnetic field gradient can be applied during the preparatory periods or the read-out periods in obtaining the data for the two images.

Claims

1. A method of selectively projection imaging material using magnetic resonance techniques comprising the steps of

obtaining first image data signals of a body using a first gradient field, the waveform of said first gradient field having a first moment of a first non-zero value,

obtaining second image data signals of said body using a second gradient field, the waveform of said second gradient field having a first moment value different from said first non-zero value, and

subtracting said first image data signals from said second image data signals wherein said first and second image data signals are vectors and the resultant signal is dependent on the phase and amplitude of said image data signals.

2. The method as defined by claim 1 wherein said first gradient field and said second gradient field are applied in a direction of flowing material within static material said step of subtracting first image data signals from said second image data signals eliminating signals from static material and providing a net signal attributable to said flowing material.

3. The method as defined by claim 2 wherein said first moment value of said second gradient field waveform is zero.

4. The method as defined by claim 2 wherein said first moment value of said second gradient field waveform is non-zero.

5. The method as defined by claim 2 wherein said first gradient field and said second gradient field are applied during slice select excitation of nuclear spins in said body.

6. The method as defined by claim 2 wherein said first gradient field and said second gradient field are applied as preparatory fields after slice select excitation and before signal readout.

7. The method as defined by claim 2 wherein said first gradient field and said second gradient field are applied for readout of nuclear spin signals.

8. Apparatus for selectively projection imaging moving material using magnetic resonance techniques comprising

first means for establishing a first magnetic field including a first magnetic gradient field for image/slice selection,

second means for exciting nuclear spins in a selected image slice,

third means for applying a second magnetic gradient following excitation of nuclear spins and a third magnetic gradient during detection of nuclear spin signals,

means for detecting nuclear spin signals during a readout period,

fourth means for subtracting first nuclear spin signals from second nuclear spin signals, said first and second nuclear spin signals resulting from the application of magnetic gradients whose waveforms have different first moments, wherein said first and second nuclear spin signals are vectors and the resultant signal is dependent on the phase and amplitude of said nuclear spin signals, and

means for imaging the difference in said nuclear spin signals to provide a projection image of moving material.

9. Appatus as defined by claim 8 wherein the selectively imaged material is blood flow, said magnetic gradients whose waveforms have different first moments are applied in a direction of a velocity component of said blood flow.

10. Apparatus as defined by claim 9 wherein said first magnetic gradient waveform has different first moments for two signal detection sequences.

11. Apparatus as defined by claim 9 wherein said second magnetic gradient waveform has different first moments for two different detection sequences during which said first nuclear spin signals and said second nuclear spin signals are detected.

12. Apparatus as defined by claim 9 wherein said third magnetic gradient has different moments for two signal detection sequences during which said first nuclear spin signals and said second nuclear spin signals are detected.

13. Apparatus as defined by claim 8 wherein the phases of said first and second detected nuclear spins for moving material are different due to differences in said first moments.

14. Apparatus for selectively projection imaging moving material using magnetic resonance techniques comprising

first means for establishing a first magnetic field including a first magnetic gradient field for image/slice selection,

second means for exciting nuclear spins in a selected image slice,

third means for applying a second magnetic gradient following excitation of nuclear spins and a third magnetic gradient during detection of nuclear spin signals,

means for detecting nuclear spin signals during a readout period,

fourth means for obtaining first image signals from a first sequence of first nuclear spin signals and second image signals from a second sequence of second nuclear spin signals, and

fifth means for subtracting the amplitudes of said first image signals from the amplitudes of said second image signals to obtain image signals of moving material, said first and second nuclear spin signals resulting from the application of magnetic gradients whose waveforms have different first moments, and means for imaging the difference in said nuclear spin signals to provide a projection image of moving material.

15. Apparatus as defined by claim 14 wherein a gradient waveform used in obtaining said first image signals has a first moment of approximately zero value.

16. A method of selectively projection-imaging material using magnetic resonance techniques comprising the steps of

obtaining first image data signals of a body using a first gradient field, the waveform of said first gradient field having a first moment of a first non-zero value,

obtaining second image data signals of said body using a second gradient field, the waveform of said second gradient field having a first moment value different from said first non-zero value, and

subtracting the amplitude of said first image data signals from the amplitude of said second image data signals.