# US 2001/0027262 A1 · Magnetic resonance angiography using undersampled 3D projection imaging

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- Number: US 2001/0027262 A1
- Document ID: US20010027262A1
- Status: Published application
- Kind: A1
- Application number: 09/767,757
- Filed: 2001-01-23
- Published: 2001-10-04
- Earliest claimed: 1998-04-10
- Assignees: Wisconsin Alumni Research Foundation
- Inventors: Charles A. Mistretta; Andrew V. Barger; Walter F. Block
- Web page: https://patentgrep.com/patent/US20010027262A1

## CPC

- G01R 33/4824: {using a non-Cartesian trajectory}
- G01R 33/54: Signal processing systems, e.g. using pulse sequences {; Generation or control of pulse sequences; Operator console}
- G01R 33/563: of moving material, e.g. flow contrast angiography
- G01R 33/281: {Means for the use of in vitro contrast agents (G01R33/282 takes precedence; involving use of a contrast agent in MR imaging G01R33/5601; in vivo contrast agents A61K49/0002)}
- G01R 33/561: by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R 33/5611: {Parallel magnetic resonance imaging, e.g. sensitivity encoding [SENSE], simultaneous acquisition of spatial harmonics [SMASH], unaliasing by Fourier encoding of the overlaps using the temporal dimension [UNFOLD], k-t-broad-use linear acquisition speed-up technique [k-t-BLAST], k-t-SENSE (structural details of arrays of sub-coils G01R33/3415)}
- G01R 33/5619: {by temporal sharing of data, e.g. keyhole, block regional interpolation scheme for k-Space [BRISK]}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A 3D projection reconstruction pulse sequence is employed to acquire CEMRA images. In one application of the invention an undersampled, high resolution abdominal CEMRA image is acquired in a single breathhold. In another application of the invention a series of undersampled image frames are acquired during a CEMRA dynamic study Each image is produced by combining peripheral k-space data from adjacent image frames with the central and peripheral k-space data of an acquired image frame.

## Claims

### Claim 1

A method for producing a magnetic resonance image of a patient using a magnetic resonance imaging (MRI) system, the steps comprising:
a) operating the MRI system to acquire a k-space image data set using a three-dimensional projection reconstruction pulse sequence that is repeated to sample k-space throughout a k-space volume having a radius R, and wherein the three-dimensional projection reconstruction pulse sequence is repeated a sufficient number of times to sample in accordance with the Nyquist condition, a central region of k-space having a radius r that is substantially smaller than the radius R but not a sufficient number of times to sample a peripheral region of k-space in accordance with the Nyquist condition; and
b) reconstructing an image using substantially the entire, undersampled acquired k-space image data set and wherein the number of repetitions of the three-dimensional projection reconstruction pulse sequence is substantially less than one-half the number of repetitions necessary to fully sample the entire k-space volume in accordance with the Nyquist condition.

### Claim 2 (depends on 1)

The method as recited in claim 1 in which step b) includes:
i) producing a three-dimensional array of k-space data by regridding the acquired k-space data set; and
ii) performing a three-dimensional Fourier transformation on the three-dimensional array of k-space data.

### Claim 3 (depends on 1)

The method as recited in claim 1 in which the resolution of the reconstructed image is isotropic.

### Claim 4 (depends on 1)

The method as recited in claim 1 in which the pulse sequence is performed by:
i) producing an rf excitation pulse that produces transverse magnetization in spins located throughout the field of view of the reconstructed image; and
ii) acquiring an NMR signal in the presence of a readout gradient to sample k-space in a trajectory that starts at one point on an outer boundary of the sampled k-space volume, passes through the center of k-space and extends out to another point on the outer boundary of the sampled k-space volume.

### Claim 5 (depends on 4)

The method as recited in claim 4 in which the sampling trajectory is a straight line.

### Claim 6 (depends on 1)

The method as recited in claim 1 in which the pulse sequence is performed by:
i) producing an rf excitation pulse that produces transverse magnetization in spins located throughout the field of view of the reconstructed image;
ii) acquiring an NMR signal in the presence of a readout gradient to sample k-space in a trajectory that extends from one point on an outer boundary of the k-space volume and extends through the center of k-space; and
the method further includes the step of synthesizing from the k-space samples acquired in step ii) further k-space samples that extend the trajectory to another point on the outer boundary of the k-space volume.

### Claim 7 (depends on 1)

The method as recited in claim 1 in which step b) includes performing a filtered back projection image reconstruction using the k-space image data set.

### Claim 8

A method for producing a magnetic resonance angiogram of selected vasculature in a patient using a magnetic resonance imaging system (MRI) system, the steps comprising:
a) injecting the patient with a contrast agent which flows into the selected vasculature;
b) operating the MRI system to perform a three-dimensional projection reconstruction pulse sequence;
c) acquiring an NMR signal produced by spins in the selected vasculature to sample k-space along a trajectory that extends substantially radially from the center of k-space;
d) repeating steps b) and c) with a different readout gradient in the three-dimensional projection reconstruction pulse sequence to sample k-space along a different trajectory that extends substantially radially from the center of k-space;
e) producing an image data set by repeating step d) to sample k-space throughout a three-dimensional k-space volume with substantially uniform spacing between trajectories and with the spacing between acquired k-space samples from adjacent trajectories at the periphery of the sampled k-space volume being substantially more than twice the spacing necessary to satisfy the Nyquist condition; and
f) reconstructing an image of the selected vasculature using substantially all the k-space samples in the acquired image data set.

### Claim 9 (depends on 8)

The method as recited in claim 8 in which step f) includes:
i) producing a three-dimensional array of k-space data by regridding the acquired k-space samples; and
ii) performing a three-dimensional Fourier transformation on the three-dimensional array of k-space data.

### Claim 10 (depends on 8)

The method as recited in claim 8 in which the resolution of the reconstructed image is isotropic throughout the selected vasculature.

### Claim 11 (depends on 8)

The method as recited in claim 8 which includes:
timing the performance of steps b) through e) such that the acquired NMR signals are enhanced by the arrival of contrast agent in the selected vasculature.

### Claim 12 (depends on 8)

The method as recited in claim 8 which includes, repeating steps b) through e) to acquire additional image data sets as the contrast agent flows into the selected vasculature, and step f) includes, combining k-space samples from a plurality of acquired image data sets, and reconstructing said image using the combined k-space samples.

### Claim 13 (depends on 12)

The method as recited in claim 12 in which successively acquired image data sets sample different locations in k-space and k-space samples from successive image data sets are combined and used to reconstruct said image.

### Claim 14 (depends on 13)

The method as recited in claim 13 in which the k-space samples from one acquired image data set are combined with peripheral region k-space samples from a successively acquired image data set.

### Claim 15 (depends on 13)

The method as recited in claim 13 in which image data sets from three different and interleaved locations in k-space are successively and repeatedly acquired, and k-space samples from three successive image data sets are combined and used to reconstruct said image.

### Claim 16 (depends on 15)

The method as recited in claim 15 in which all the k-space samples from the second of said three successive image data sets are combined with peripheral region k-space samples from the first and the third of said three successive image data sets.

### Claim 17 (depends on 16)

The method as recited in claim 16 in which the spacing between k-space samples in a central region of each image data set satisfies the Nyquist condition.

### Claim 18 (depends on 12)

The method as recited in claim 12 in which the three-dimensional projection reconstruction pulse sequence produces a velocity encoding gradient;
successively acquired image data sets are velocity encoded for spin motion along different axes; and
k-space samples from successively acquired image data sets are combined and used to reconstruct said image.

### Claim 19 (depends on 18)

The method as recited in claim 18 in which image data sets with three different velocity encoding directions are successively acquired, and k-space samples from three successive image data sets are combined and used to reconstruct said image.

### Claim 20 (depends on 13)

The method as recited in claim 13 in which the radial k-space sampling trajectories of the different image data sets are interleaved.

### Claim 21 (depends on 8)

The method as recited in claim 8 in which the k-space sampling trajectories acquired in step c) extend from the center of k-space in substantially opposite directions therefrom and to substantially opposite points on an outer boundary of the sampled k-space volume.