MAGNETIC RESONANCE IMAGING USING ADDITIONAL GRADIENT PULSES

• US 20200132795A1
• Filed: 10/28/2019
• Published: 04/30/2020
• Est. Priority Date: 10/29/2018
• Status: Active Grant

• Current Assignee: Siemens Healthineers AG (Siemens AG)
• Original Assignee: Siemens Healthcare GMBH (Siemens AG)
• Inventors: Beck, Thomas, Polak, Daniel
• Granted Patent: US 10,935,618 B2
• Time in Patent Office: Days
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/482 using a Cartesian trajectory
• CPC Class Codes: G01R 33/4835 of multiple slices
• CPC Class Codes: G01R 33/543 Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription G01R33/546 takes precedence
• CPC Class Codes: 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
• CPC Class Codes: G01R 33/5613 Generating steady state signals, e.g. low flip angle sequences [FLASH]
• CPC Class Codes: G01R 33/56572 caused by a distortion of a gradient magnetic field, e.g. non-linearity of a gradient magnetic field G01R33/56509, G01R33/56518, G01R33/56536 take precedence
• CPC Class Codes: G01R 33/58 Calibration of imaging systems, e.g. using test probes , Phantoms; Calibration objects or fiducial markers such as active or passive RF coils surrounding an MR active material

Abstract

Method for MR imaging of an acquisition region during a patient examination. In order to determine a point spread function, in a prior measurement for each of additional gradient output directions, the method includes choosing, in the acquisition region, a slice lying outside of an isocenter of the MR device, which slice extends in a plane perpendicular to the additional gradient output direction under consideration; following a respective slice-selective excitation of the selected slice, acquiring first calibration data using the additional gradient pulse of the additional gradient output direction under consideration, and acquiring second calibration data omitting the additional gradient pulse in each case along a k-space line, wherein a same timing sequence of additional gradient pulse and readout time window is used as in the MR sequence; and calculating, from the first and second calibration data, the point spread function for the additional gradient output direction under consideration.

Claims

1. A method for magnetic resonance imaging of an acquisition region during an examination of a patient by means of a magnetic resonance device, using a magnetic resonance sequence which applies an additional gradient pulse of a predefined gradient shape along at least one additional gradient output direction perpendicular to a readout direction during a readout time window of the magnetic resonance sequence referred to a k-space line during Cartesian sampling, using a point spread function describing an actual sampling trajectory distorted by the additional gradient pulse in order to determine a magnetic resonance dataset from magnetic resonance signals acquired by means of the magnetic resonance sequence to take into account the additional gradient pulse, wherein in order to determine the point spread function, in a prior measurement for each of the additional gradient output directions, the method comprising:

choosing, in the acquisition region, a slice lying outside of the isocenter of the magnetic resonance device, which slice extends in a plane perpendicular to the additional gradient output direction under consideration;

following a respective slice-selective excitation of the selected slice, acquiring first calibration data using the additional gradient pulse of the additional gradient output direction under consideration, and acquiring second calibration data omitting the additional gradient pulse in each case along a k-space line, wherein a same timing sequence of additional gradient pulse and readout time window is used as in the magnetic resonance sequence; and

calculating, from the first and second calibration data, the point spread function for the additional gradient output direction under consideration.

2. The method as claimed in claim 1, further comprising:

realizing a Wave-CAIPI method by using a sinusoidal gradient shape for the additional gradient pulse.

3. The method as claimed in claim 1, further comprising:

choosing the k-space line that is to be read out from the selected slice as a k-space line intersecting the k-space center.

4. The method as claimed in claim 1, further comprising:

repeating the acquisition of the first and second calibration data multiple times for statistical combining.

5. The method as claimed in claim 1, further comprising:

selecting, in the acquisition region, a slice spaced at a furthest possible distance from the isocenter and containing a part of the object.

6. The method as claimed in claim 1, further comprising recalculating the point spread function without reacquisition of calibration data if there is a change in a resolution for the examination that is to be carried out or a change in a position of the acquisition region.

7. The method as claimed in claim 1, wherein the acquisition of the first and second calibration data comprises a FLASH imaging technique.

8. A magnetic resonance device, comprising:

a controller configured to perform the method as claimed in claim 1.

9. A non-transitory computer-readable medium comprising a computer program for performing the steps of the method of claim 1, when executed on a control device of a magnetic resonance device.