Method and apparatus for efficient stenosis identification and assessment using MR imaging

• US 6,741,880 B1
• Filed: 06/16/2000
• Issued: 05/25/2004
• Est. Priority Date: 06/16/2000
• Status: Expired due to Term

• Current Assignee: General Electric Company, Uniformed Services University of the Health Sciences (Government of the United States of America)
• Original Assignee: General Electric Company
• Inventors: Ho, Vincent B., Saranathan, Manojkumar, Foo, Thomas K. F.
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): Jung, William C.
• Application Number:
  US09/595,117
• Time in Patent Office: 1,439 Days
• Field of Search: 600/410, 600/419, 600/420, 600/407, 382/128, 324/300, 324/307
• US Class Current: 600/419
• CPC Class Codes: A61B 5/0263 using NMR
• CPC Class Codes: G01R 33/54 Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
• CPC Class Codes: G01R 33/56 Image enhancement or correction, e.g. subtraction or averaging techniques , e.g. improvement of signal-to-noise ratio and resolution

Abstract

A method and apparatus is disclosed in which a two-tiered approach is taken to first grade a patient to identify the presence of any suspected stenosis, and then a second step is used to acquire more detailed information to grade the stenosis. The invention includes performing a screening study by acquiring a first MR image having a low resolution to scan a suspected stenosis region. After analyzing the first MR image to identify a suspected stenosis within the suspected stenosis region, a more detailed study is performed by acquiring a second MR image having a higher resolution than the first MR image to scan the identified suspected stenosis. If no lesions, or stenotic vessels, are identified after the first MR image, the second MR image need not be obtained. Since the first MR image is designed to be more sensitive to the detection of such stenosis, by increasing the conspicuity of the lesions, and using a fast acquisition sequence, this two-tiered approach increases the efficiency for accurate coronary artery stenosis detection and assessment.

Claims

1. A method of identifying a stenotic vessel using MR imaging comprising the steps of:

performing a screening study by;

acquiring a first MR image having a low resolution to scan a suspected stenosis region;

analyzing the first MR image to identify a suspected stenosis within the suspected stenosis region;

performing a detailed study by;

acquiring a second MR image having a higher resolution than the first MR image to scan the identified suspected stenosis; and

analyzing the second MR image to identify an actual stenosis.

2. The method of claim 1 further comprising the step of grading the actual stenosis using the second MR image.

3. The method of claim 1 wherein the first MR image acquired provides high sensitivity to lesion detection in the blood vessel.

4. The method of claim 1 wherein the steps of acquiring a second MR image and analyzing the second MR image are conditional upon identifying a suspected stenosis in the step of analyzing the first MR image.

5. The method of claim 1 further comprising the step of applying a pulse sequence with at least one flow-sensitizing bi-polar gradient.

6. The method of claim 5 further comprising the step of initially setting a velocity encoding (VENC) value of a first moment of the at least one flow-sensitizing bi-polar gradient to a nominally low value to establish a velocity distribution greater than 2p within each voxel.

7. The method of claim 1 wherein the step of analyzing the first MR image includes detecting flow voids as an indication of a suspected stenosis.

8. The method of claim 1 wherein the first MR image is acquired with high phase cancellation using at least one of:

(1) applying a pulse sequence with bi-polar gradients to accentuate phase cancellation; and

(2) increasing voxel size for greater distribution of velocity vectors;

to thereby increase flow dephasing.

9. The method of claim 1 wherein the second MR image is acquired with low phase cancellation and high resolution in order to isolate and grade the suspected stenosis by at least one of:

(1) comparing diameters of the blood vessel along a length of the suspected stenosis; and

(2) comparing a velocity gradient along the length of the suspected stenosis.

10. The method of claim 1 wherein the step of acquiring a first MR image includes applying a pulse sequence with bi-polar gradients to accentuate phase cancellation and thereby increase flow dephasing.

11. The method of claim 1 wherein the step of acquiring a first MR image includes increasing voxel size for greater distribution of velocity vectors to thereby increase flow dephasing.

12. An examination method to identify a lesion in a blood vessel and grade a stenosis resulting therefrom comprising the step of:

acquiring a first MR image using a gradient echo imaging pulse sequence having a flow sensitizing bi-polar gradient waveform;

detecting and localizing a suspected stenosis using the first MR image;

if a stenosis is detected and localized, acquiring a second MR image having a higher resolution than the first MR image in a region in which the suspected stenosis is detected and localized to grade the suspected stenosis; and

if a stenosis is not detected and localized in the step detecting and localizing, ending the examination method without further MR image acquisition.

13. The method of claim 12 wherein the first MR image is a low resolution image with high sensitivity to velocity flow for detecting a lesion on a blood vessel.

14. The method of claim 13 wherein the step of detecting a lesion includes detecting velocity flow voids in the first MR image.

15. The method of claim 12 further comprising the step of increasing intra-voxel flow dephasing effects.

16. The method of claim 12 further comprising the step of applying flow sensitizing gradients in all three directions to provide insensitivity to orientation of the blood vessel.

17. The method of claim 12 wherein the first MR image is acquired with high phase cancellation to increase flow dephasing using at least one of:

(1) applying a pulse sequence with bi-polar gradients to accentuate phase cancellation; and

(2) increasing voxel size for greater distribution of velocity vectors.

18. The method of claim 12 wherein the second MR image is acquired to isolate and grade the suspected stenosis by at least one of:

(1) comparing diameters of the blood vessel along a length of the suspected stenosis; and

(2) comparing a velocity gradient along the length of the suspected stenosis.

19. An MRI apparatus to conduct MR stenosis screening, and if necessary, grade a stenotic vessel comprising:

a magnetic resonance imaging (MRI) system having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images; and

a computer programmed to operate the MRI system in two modes to efficiently conduct a stenosis exam,

the first mode programmed to;

acquire at least one first MR image with low resolution over a relatively large region;

allow a user to analyze the at least one first MR image for an indication of a suspected stenosis;

receive input to either end the stenosis exam or switch to the second mode;

the second mode programmed to;

create a localized region of the relatively large region to target the suspected stenosis; and

acquire at least one second MR image with resolution higher than that of the at least one first MR image of the localized region.

20. The MRI apparatus of claim 19 wherein the computer is further programmed to:

use a first pulse sequence for the acquisition of the at least one first MR image, the first pulse sequence having a flow-sensitizing bi-polar gradient waveform; and

use a second pulse sequence for the acquisition of the at least one second MR image, the second pulse sequence providing less phase cancellation than the first pulse sequence.

21. The MRI apparatus of claim 20 wherein the first pulse sequence includes a VENC value of a first moment of the flow-sensitizing bi-polar gradient waveform set to a nominally low value.

22. The MRI apparatus of claim 21 wherein the VENC value is set substantially lower than that of the second pulse sequence.

23. The MRI apparatus of claim 19 wherein an encoded velocity distribution is greater than 2p within each voxel for the first MR image.

24. The MRI apparatus of claim 19 wherein the computer is further programmed to increase flow dephasing in the first MR image.

25. The MRI apparatus of claim 24 wherein the increase in flow dephasing is accomplished by an increase in voxel size for greater distribution of velocity vectors.

26. A computer readable storage medium having stored thereon a computer program comprising instructions which, when executed by a computer, cause the computer to:

acquire a first MR image of a relatively large region, the first MR image having high phase cancellation to screen a patient for possible arterial lesions; and

limit a FOV to a target region within the relatively large region if a possible arterial lesion is located, then

acquire a second MR image of the targeted region, the second MR image having a resolution higher than that of the first MR image.

27. The computer readable storage medium of claim 26 wherein the first MR image is acquired with high phase cancellation using at least one of:

(1) applying a pulse sequence with bi-polar gradients to accentuate phase cancellation; and

(2) increasing voxel size for greater distribution of velocity vectors;

to thereby increase flow dephasing.

28. The computer readable storage medium of claim 26 wherein the computer is further programmed to:

use a first pulse sequence for the acquisition of the at least one first MR image, the first pulse sequence having a flow-sensitizing bi-polar gradient waveform; and

use a second pulse sequence for the acquisition of the at least one second MR image, the second pulse sequence providing less phase cancellation than the first pulse sequence.

29. The computer readable storage medium of claim 26 wherein the computer is further programmed to:

apply a pulse sequence with at least one flow-sensitizing bi-polar gradient; and

initially set a velocity encoding (VENC) value of a first moment of the at least one flow-sensitizing bi-polar gradient to a nominally low value to establish a velocity distribution greater than 2p within each voxel.

30. The computer readable storage medium of claim 26 wherein the computer is further programmed to detect lesions by detecting velocity flow voids in the first MR image.

31. The computer readable storage medium of claim 26 wherein the computer is further programmed to acquire the second MR image with low phase cancellation and high resolution in order to isolate and grade the suspected stenosis by at least one of:

(1) comparing diameters of the blood vessel along a length of the suspected stenosis; and

(2) comparing a velocity gradient along the length of the suspected stenosis.