Contrast detection and guided reconstruction in contrast-enhanced magnetic resonance angiography

• US 6,195,579 B1
• Filed: 12/18/1998
• Issued: 02/27/2001
• Est. Priority Date: 12/18/1998
• Status: Expired due to Term

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Mistretta, Charles A., Carroll, Timothy J.
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): SHAW, SHAWNA JEANNINE
• Application Number:
  US09/215,755
• Time in Patent Office: 802 Days
• Field of Search: 600/420, 600/410, 600/419, 324/306, 324/309, 382/130
• US Class Current: 600/420
• CPC Class Codes: G01R 33/561 by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
• CPC Class Codes: G01R 33/56308 Characterization of motion or flow; Dynamic imaging

Abstract

A dynamic MRA study is performed using a 3D fast gradient recalled echo pulse sequence. A signal strength indicator for each acquired k-space data set is calculated and these indicator values are employed to produce a contrast curve. This contrast curve is used to select data for use in forming a CONTRAST k-space data set and a MASK k-space data set. The MASK is subtracted from the CONTRAST data set and the result is used to reconstruct an image.

Claims

1. A method for producing a contrast enhanced MRA image of a subject using an MRI system, the steps comprising:

a) injecting a contrast agent into the subject;

b) acquiring a series of k-space data sets over a period of time during which the contrast agent enters a region of interest in the subject being imaged;

c) calculating a signal strength indicator for each k-space data set from k-space data therein;

d) selecting a first k-space data set having a high calculated signal strength indicator to form a final k-space data set; and

e) reconstructing an image using the final k-space data set.

2. The method as recited in claim 1 in which the signal strength indicator for a k-space data set is calculated by summing together the square root of the sum of the square of a real component and the square of an imaginary component for a set of k-space samples in the k-space data set.

3. The method as recited in claim 1 which includes:

f) selecting a second k-space data set having a low calculated signal strength indicator; and

g) subtracting the second k-space data set from the first k-space data set to form the final k-space data set.

4. The method as recited in claim 1 in which an additional k-space data set having a calculated signal strength indicator above a threshold amount is combined with the first k-space data set to form a CONTRAST k-space data set which is used to form the final k-space data set.

5. The method as recited in claim 4 which includes:

f) selecting and combining together to form a MASK k-space data set a plurality of k-space data sets having calculated signal strength indicators below a second threshold amount; and

g) subtracting the MASK k-space data set from the CONTRAST k-space data set to form the final k-space data set.

6. The method as recited in claim 1 which includes:

producing a contrast curve using the calculated signal strength indicators of k-space data sets; and

step d) is performed by selecting a k-space data set near the peak value indicated by the contrast curve.

7. The method as recited in claim 1 in which the acquired k-space data sets include:

a plurality of central region k-space data sets that each contain k-space samples from a central region of k-space; and

a plurality of peripheral region k-space data sets that each contain k-space samples from a peripheral region of k-space.

8. The method as recited in claim 7 which includes:

renormalizing the calculated signal strength indicators for each acquired k-space data set; and

producing a contrast curve using the renormalized signal strength indicators for k-space data sets; and

step d) is performed by selecting a central region k-space data set and a peripheral k-space data set near a peak value in the contrast curve.

9. The method as recited in claim 7 in which the final k-space data set is formed by selecting a central region k-space data set having a high signal strength indicator and combining it with a selected peripheral region k-space data set having a high signal strength indicator.

10. The method as recited in claim 7 in which the final k-space data set is formed by averaging a plurality of central region k-space data sets having high signal strength indicators and combining it with the average of a plurality of peripheral region k-space data sets having high signal strength indicators.

11. The method as recited in claim 9 which includes:

f) selecting a second k-space data set by combining a central region k-space data set having a low signal strength indicator with a peripheral region k-space data set having a low signal strength indicator; and

g) subtracting the second k-space data set from the first k-space data set to form the final k-space data set.

12. The method as recited in claim 1 in which the image is reconstructed by Fourier transforming the final k-space data set.

13. The method as recited in claim 1 in which step d) includes selecting a plurality of said k-space data sets and combining the selected k-space data sets to form the final k-space data set.

14. The method as recited in claim 13 which includes:

calculating the mean value of the signal strength indicators of the k-space data sets; and

weighting each selected k-space data set before combining it to form the final k-space data set.

15. The method as recited in claim 14 in which the weighting is performed by multiplying values in the selected k-space data set by a weighting factor proportional to the difference between the mean value of the signal strength indicators of the k-space data sets and the signal strength indicator of the selected k-space data set.

16. A method for detecting the arrival of an injected contrast agent in a field of view in a subject placed in an MRI system, the steps comprising:

a) performing a pulse sequence with the MRI system to acquire NMR data which samples k-space in the field of view;

b) repeating step a) a plurality of times to acquire a plurality of k-space samples from the field of view;

c) calculating a signal strength indicator for the acquired plurality of k-space samples;

d) repeating steps a) through c) a plurality of times to produce a series of calculated signal strength indicators; and

e) indicating the arrival of the contrast agent in the field of view when a calculated signal strength indicator exceeds a threshold value.

17. The method as recited in claim 16 in which a time delay Δ

t is measured between the injection of the contrast agent in the subject and its indicated arrival in the field of view.

18. The method as recited in claim 17 in which a second injection of contrast agent is made in the patient and an MRA image is acquired with the MRI system by:

signaling the patient to breath-hold at a time after the second injection based upon the value Δ

t;

acquiring NMR image data after commencement of the breath-hold; and

reconstructing an MRA image from the acquired NMR image data.