Accelerated Shells Trajectory MRI Acquisition

• US 20080183067A1
• Filed: 01/24/2008
• Published: 07/31/2008
• Est. Priority Date: 01/26/2007
• Status: Active Grant

• Current Assignee: Mayo Foundation For Medical Education And Research (Mayo Clinic)
• Original Assignee: Mayo Foundation For Medical Education And Research (Mayo Clinic)
• Inventors: Bernstein, Matthew A., Shu, Yunhong
• Granted Patent: US 8,214,013 B2
• Time in Patent Office: Days
• US Class Current: 600/410
• CPC Class Codes: G01R 33/4824 using a non-Cartesian trajectory
• 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 33/5635 Angiography, e.g. contrast-enhanced angiography [CE-MRA] or time-of-flight angiography [TOF-MRA]

Abstract

A method for prescribing a scan on an MRI system includes selecting a general pulse sequence to be used during a time-resolved imaging process of a subject using an MRI system. The method also includes setting a first set of scan parameters to more specifically prescribe the general pulse sequence and setting a second set of scan parameters using a formula that relates time resolution and spatial resolution resulting from the first set of scan parameters. The method then includes performing the time-resolved imaging process using the general pulse sequence, the first set of scan parameters, and the second set of scan parameters.

Claims

1. A method for prescribing a scan on an MRI system, the steps comprising:

a) selecting a general pulse sequence to be used during an time-resolved imaging process of a subject using an MRI system;

b) setting a first set of scan parameters to more specifically prescribe the general pulse sequence;

c) setting a second set of scan parameters using a formula that relates time resolution and spatial resolution resulting from the first set of scan parameters; and

d) performing the time-resolved imaging process using the general pulse sequence, the first set of scan parameters, and the second set of scan parameters.

2. The method of claim 1 wherein the general pulse sequence includes a shell pulse sequence and the first set of scan parameters includes a number of fixed scan parameters including a flip angle and field of view.

3. The method of claim 1 wherein step c) includes setting variable scan parameters including temporal resolution and spatial resolution using the formula and the first set of scan parameters.

4. The method of claim 1 wherein the second set of scan parameters include scan parameters that can be changed to affect the spatial readout time resolution of the time-resolved scan.

5. The method of claim 1 wherein the formula controls a trade-off between spatial and temporal resolution of the time-resolved imaging process by adjusting a multi-dimensional k-space cutoff radius parameter, K_c.

6. The method of claim 1 wherein the formula provides a quantitative criterion to specify particular time-frames in the time-resolved imaging process acquired using the general pulse sequence with the first set of scan parameters in various regions of the spatial k-space.

7. The method of claim 1 wherein the formula is:

$f_t=\frac{1}{\mathrm{\Delta <br><br>}<br><br><br><br>t}<br><br>\sqrt{1-{\left(\frac{k_x}{k_{0<br><br>x}}\right)}^2-{\left(\frac{k_y}{k_{0<br><br>y}}\right)}^2-{\left(\frac{k_z}{k_{0<br><br>z}}\right)}^2}$

where;

k_0x=extent of k-space sampling along x-axis;

k_0y=extent of k-space sampling along y-axis;

k_0z=extent of k-space sampling along z-axis;

Δ

t=temporal resolution of acquired image frames; and

f_t=is the sampling frequency of acquired image frames.

8. The method of claim 7 wherein step d) includes a Cartesian acquisition and wherein k_x is sampled along a parallel path for each readout so that the formula reduces to:

$f_t=\frac{1}{\mathrm{\Delta <br><br>}<br><br><br><br>t}<br><br>\sqrt{1-{\left(\frac{k_y}{k_{0<br><br>y}}\right)}^2-{\left(\frac{k_z}{k_{0<br><br>z}}\right)}^2}.$

9. The method of claim 1 wherein the second set of scan parameters is selected to determine a degree of undersampling to include in the time-resolved imaging process.

10. The method of claim 1 wherein the general pulse sequence employs a shell k-space sampling trajectory of a prescribed radius and a prescribed transmit repeat time (TR).

11. The method of claim 10 wherein step d) includes repeatedly performing the general pulse sequence using the first set of scan parameters and the second set of scan parameters a plurality of times at different prescribed radii to acquire a k-space image data set, and wherein the prescribed TR for small radii shell trajectories is shorter than the prescribed TR for large radii shell trajectories.

12. The method of claim 11 further comprising step e) reconstructing an image of the subject from the k-space image data set.

13. The method of claim 11 wherein peripheral k-space is sampled with a plurality of interleaved shell trajectories, each having a respective radius.

14. The method of claim 13 wherein step d) includes deleting interleaved shell trajectories in accordance with the result of step c).

15. The method of claim 13 wherein each respective radius of the interleaved shell trajectories have the same radius.

16. The method of claim 13 wherein each repetition of the general pulse sequence has a prescribed readout time and the readout time for small radii shell trajectories is shorter than the readout time for large radii shell trajectories.