MRI navigator methods and systems

• US 7,561,909 B1
• Filed: 09/16/2002
• Issued: 07/14/2009
• Est. Priority Date: 09/16/2002
• Status: Active Grant

• Current Assignee: United States Department Of Health And Human Services (Government of the United States of America)
• Original Assignee: United States Department Of Health And Human Services (Government of the United States of America)
• Inventors: Wen, Han, Pai, Vinay M.
• Primary Examiner(s): Winakur; Eric F
• Assistant Examiner(s): Fernandez; Katherine L
• Application Number:
  US10/244,903
• Time in Patent Office: 2,493 Days
• Field of Search: 600/410, 600/411, 600/413, 600/419, 600/407, 324/307, 324308-309
• US Class Current: 600/410
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/7292 Prospective gating, i.e. predicting the occurrence of a physiological event for use as a synchronisation signal
• CPC Class Codes: G01R 33/5613 Generating steady state signals, e.g. low flip angle sequences [FLASH]
• CPC Class Codes: G01R 33/56316 involving phase contrast techniques
• CPC Class Codes: G01R 33/56509 due to motion, displacement or flow, e.g. gradient moment nulling G01R33/567 takes precedence
• CPC Class Codes: G01R 33/5673 Gating or triggering based on a physiological signal other than an MR signal, e.g. ECG gating or motion monitoring using optical systems for monitoring the motion of a fiducial marker
• CPC Class Codes: G01R 33/5676 Gating or triggering based on an MR signal, e.g. involving one or more navigator echoes for motion monitoring and correction

Abstract

Navigator methods are disclosed that are based on detecting a flow-sensitive signal within a subject, and using the position of the signal to track subject motion between imaging sequences. In a disclosed embodiment, the fast-moving blood volume in the left ventricle of the heart is detected and used as a reference point to correct for cardiac motion that results from respiratory motion in a subject. The navigator based on the position of the fast-moving blood volume in the left ventricle may be applied prospectively to shift a subsequent imaging slice to compensate for subject motion, and thereby provide MRI images with increased clarity and resolution.

Claims

1. A method for correcting a magnetic resonance image for subject motion during image acquisition, comprising:

exciting a volume within a subject with a flow encoded pulse sequence;

detecting a flow-sensitive signal associated with blood flow within the volume of the subject;

identifying a reference position within the volume based on the flow-sensitive signal; and

using the reference position as a navigator for tracking and correcting for subject motion between image acquisition events.

2. The method of claim 1, wherein the volume excited is a volume that includes at least a portion of the left ventricle of the heart.

3. The method of claim 2, wherein exciting occurs at mid-systole or mid-diastole.

4. The method of claim 1, wherein the flow encoded pulse sequence comprises a bipolar velocity-encoding gradient.

5. The method of claim 4, wherein the flow encoded pulse sequence comprises a FLASH sequence incorporating the bipolar velocity-encoding gradient.

6. The method of claim 4, wherein detecting comprises calculating the complex difference between a transverse magnetization detected after a first bipolar velocity encoding gradient, and a transverse magnetization detected after a second bipolar gradient.

7. The method of claim 1, wherein the reference position is used to prospectively shift a position of a subsequent k-space imaging slice to compensate for subject motion between a first imaging sequence of pulses and a second imaging sequence of pulses.

8. A method for correcting a magnetic resonance image of the heart for subject motion during image acquisition, comprising:

exciting a region of a subject including at least a portion of the blood volume of the heart with a flow-encoded pulse sequence;

detecting a signal associated with blood flow in the heart based on the flow-encoded pulse sequence;

determining a position associated with blood flow in the heart based on the detected signal; and

using the determined position as a reference position for correcting the image of the heart for subject motion during image acquisition.

9. The method of claim 8, wherein the volume excited is a volume that includes at least a portion of the left ventricle of the heart.

10. The method of claim 9, wherein exciting occurs at mid-systole or mid-diastole.

11. The method of claim 8, wherein the flow-encoded pulse sequence comprises a bipolar velocity-encoding gradient.

12. The method of claim 11, wherein the flow-encoded pulse sequence comprises a FLASH sequence incorporating the bipolar velocity-encoding gradient.

13. The method of claim 11, wherein the detecting comprises calculating the complex difference between a transverse magnetization detected after a first bipolar velocity encoding gradient, and a transverse magnetization detected after a second bipolar gradient.

14. The method of claim 8, wherein the reference position is used to prospectively shift a position of a subsequent k-space imaging slice to compensate for subject motion between a first imaging sequence of pulses and a second imaging sequence of pulses.

15. A method for correcting for subject motion in an MRI image, comprising:

exciting a volume within a subject with a flow-encoded pulse sequence;

detecting a flow-sensitive signal associated with fluid flow in the volume;

calculating a current position within the volume based on the detected signal relative to a reference position previously established based on a reference flow-sensitive signal; and

translating a subsequent imaging slice to compensate for a difference between the current and reference positions.

16. The method of claim 15, wherein the volume includes at least a portion of the blood volume of the heart.

17. The method of claim 16, wherein exciting is timed relative to an ECG signal to occur at mid-systole or mid-diastole.

18. The method of claim 15, wherein the detecting comprises calculating the complex difference between a transverse magnetization detected after a first bipolar velocity encoding gradient, and a transverse magnetization detected after a second bipolar gradient.

19. The method of claim 18, wherein calculating a current position relative to a reference position comprises applying a one-dimensional Fast Fourier transform to a complex difference calculated for the reference flow-sensitive signal to provide a reference spectrum, applying a one-dimensional Fast Fourier transform to the current flow-sensitive signal to provide a current spectrum, multiplying the current spectrum with a mirror image of the reference spectrum to provide a product, and applying a Fast Fourier transform to the product to provide a measure of the difference between the current and reference positions.

20. An MRI system, comprising:

a magnet for producing a polarizing magnetic field;

an RF system for exciting spins in a subject positioned in the polarizing magnetic field;

a gradient system for producing magnetic field gradients in the subject;

a pulse generator connected to the RF system and the gradient system and capable of providing a flow-encoded pulse sequence; and

a computer system, the computer system having stored thereon computer-executable instructions for generating a blood flow-sensitive navigator signal and for shifting an imaging slice in response to a change in position of the subject based on the blood flow sensitive navigator signal.

21. An MRI system, comprising:

a magnet for producing a polarizing magnetic field;

an RF system for exciting spins in a subject positioned in the polarizing magnetic field;

a gradient system for producing magnetic field gradients in the subject;

a pulse generator connected to the RF system and the gradient system and capable of providing a flow-encoded pulse sequence; and

a computer system, the computer system having stored thereon computer-executable instructions for carrying out the method comprising;

exciting a volume within a subject with a flow-encoded pulse sequence;

detecting a flow-sensitive signal associated with blood flow within the volume of the subject;

identifying a reference position within the volume based on the flow-sensitive signal; and

using the reference position as a navigator for tracking subject motion between image acquisition events.

22. A computer-readable medium having stored thereon computer-executable instructions for implementing a method comprising:

exciting a volume within a subject with a flow-encoded pulse sequence;

detecting a flow-sensitive signal associated with blood flow within the volume of the subject;

identifying a reference position within the volume based on the flow-sensitive signal; and

using the reference position as a navigator for tracking subject motion between image acquisition events.

23. A computer-readable medium having stored thereon computer-executable instructions for implementing a method comprising:

exciting a region of a subject including at least a portion of the blood volume of the heart with a flow-encoded pulse sequence;

detecting a signal associated with blood flow in the heart at a position within the region of the subject excited by the flow-encoded pulse sequence; and

using the position of the signal as a reference position for correcting the image of the heart for subject motion during image acquisition.

24. A computer-readable medium having stored thereon computer-executable instructions for implementing a method comprising:

exciting a volume within a subject with a flow-encoded pulse sequence;

detecting a flow-sensitive signal associated with fluid flow in the volume;

calculating a current position within the volume based on the detected signal relative to a reference position previously established based on a reference flow-sensitive signal; and

translating a subsequent imaging slice to compensate for a difference between the current and reference positions.

25. A method for compensating subject motion in an MRI image, comprising:

exciting a volume within a subject with a motion-encoded pulse sequence;

detecting a motion-sensitive signal associated with subject motion in the volume based on the motion-encoded pulse sequence;

calculating a current position within the volume based on the detected motion sensitive-signal relative to a reference position; and

compensating a subsequent imaging slice based on a difference between the current and reference positions.

26. The method of claim 25, wherein the excited volume includes at least a portion of the left ventricle of the heart.

27. The method of claim 26, wherein exciting occurs at mid-systole or mid-diastole.

28. The method of claim 25, wherein the motion-encoded pulse sequence comprises a bipolar velocity-encoding gradient.

29. The method of claim 28, wherein the motion-encoded pulse sequence comprises a FLASH sequence incorporating the bipolar velocity-encoding gradient.

30. The method of claim 28, wherein the current position within the volume is calculated with respect to the reference position based on a complex difference between a transverse magnetization detected after a first bipolar velocity-encoding gradient, and a transverse magnetization detected after a second bipolar velocity-encoding gradient.

31. The method of claim 25, further comprising prospectively shifting a position of a subsequent imaging slice to compensate for subject motion between a first imaging sequence and a second imaging sequence.