Pre-emphasis techniques based on temperature dependent gradient system behavior for trajectory correction in magnetic resonance imaging

Patent metadata

Field	Value
Publication number	US-11112472-B2
Application number	US-201916699415-A
Country	US
Kind code	B2
Filing date	Nov 29, 2019
Priority date	Apr 18, 2019
Publication date	Sep 7, 2021
Grant date	Sep 7, 2021

Abstract

A gradient system characterization function (e.g., a gradient system transfer function) may be developed by measuring a behavior of the MR device at a target temperature and developing at least one gradient system characterization function for a gradient coil of a magnetic resonance (MR) device at the target temperature based on the measured behavior. A patient may be subsequently imaged by the MR device, wherein the imaging process comprises measuring a temperature of a gradient coil, determining a gradient system characterization function at the measured temperature, calculating a pre-emphasized gradient of the gradient coil, and imaging the patient using the pre-emphasized magnetic field component.

First claim

The invention claimed is:

1. A method for developing at least one gradient system characterization function for a magnetic resonance (MR) device, the method comprising:
setting at least one gradient coil of the MR device at a target temperature;
measuring a behavior of the MR device at the target temperature at different frequencies of the at least one gradient coil, wherein the different frequencies are generated by varying current through the at least one gradient coil; and
developing, by a processor of the MR device, at least one gradient system characterization function for the at least one gradient coil of the MR device at the target temperature based on the measured behavior.

2. The method of claim 1 , wherein the gradient system characterization function is a gradient system transfer function.

3. The method of claim 2 , wherein the gradient system transfer function is developed for a zeroth order, first order, second order, third order field term, or a combination thereof.

4. The method of claim 1 , further comprising:
repeating the setting, the measuring, and the developing for at least one additional target temperature to provide a plurality of gradient system characterization functions for the at least one gradient coil of the MR device at a plurality of target temperatures; and
storing the plurality of gradient system characterization functions in a database of the MR device.

5. The method of claim 4 , wherein the plurality of target temperatures is predetermined by an operating temperature range of the MR device.

6. The method of claim 4 , wherein the plurality of gradient system characterization functions is a plurality of gradient system transfer functions,
wherein the at least one gradient coil comprises a first gradient coil for an x-axis, a second gradient coil for a y-axis, and a third gradient coil for a z-axis of the MR device,
wherein the behavior of the MR device is measured independently for each gradient coil at each target temperature, and
wherein a gradient system transfer function is developed for each axis of the MR device at each target temperature of the plurality of target temperatures.

7. The method of claim 1 , wherein the setting of the target temperature comprises heating at least one gradient coil by running an electrical current through the at least one gradient coil.

8. The method of claim 1 , wherein the target temperature of the MR device is monitored by at least one temperature sensor associated with a respective gradient coil.

9. A method of imaging a patient using a magnetic resonance (MR) device, the method comprising:
measuring a temperature of at least one gradient coil of the MR device using at least one temperature sensor associated with the respective gradient coil;
determining, using a processor of the MR device, a gradient system characterization function for the at least one gradient coil based on the measured temperature of the respective gradient coil;
calculating a pre-emphasized gradient for the at least one gradient coil using the determined gradient system characterization function; and
imaging the patient using the pre-emphasized gradient.

10. The method of claim 9 , wherein the at least one temperature sensor comprises a plurality of temperature sensors, and
wherein the measured temperature of the respective gradient coil is based on temperature measurements for more than one temperature sensor of the plurality of temperature sensors.

11. The method of claim 9 , wherein the determining of the gradient system characterization function comprises:
retrieving, from a database of the MR device, at least one stored characterization function for the respective gradient coil, each stored characterization function based on a measured behavior of the MR device at a target temperature at different frequencies of the respective gradient coil which has been generated by through a varying of current through the respective gradient coil; and
modeling, by the processor, the gradient system characterization function using the at least one stored characterization function and any temperature difference between the measured temperature of the respective gradient coil and the target temperature of a respective stored characterization function.

12. The method of claim 11 , wherein the modeling comprises interpolating the gradient system characterization function for the measured temperature between a first stored transfer function at a target temperature greater than the measured temperature and a second stored characterization function at a target temperature less than the measured temperature.

13. The method of claim 11 , wherein the modeling comprises extrapolating the gradient system characterization function for the measured temperature from at least two stored characterization functions having target temperatures that are either greater than or less than the measured temperature.

14. The method of claim 9 , wherein the at least one gradient coil comprises a plurality of gradient coils including a first gradient coil for an x-axis, a second gradient coil for a y-axis, and a third gradient coil for a z-axis of the MR device,
wherein temperatures are measured for each gradient coil of the plurality of gradient coils,
wherein gradient system characterization functions are determined for each gradient coil of the plurality of gradient coils,
wherein pre-emphasized gradients are calculated for each gradient coil of the plurality of gradient coils, and
wherein the patient is imaged using the pre-emphasized gradients for the plurality of gradient coils.

15. The method of claim 9 , wherein the gradient system characterization function is a gradient system transfer function.

16. The method of claim 15 , wherein the pre-emphasized gradient is a first order magnetic field term calculated using the following formula:
g pre,1 T ( t )= −1 {G nom,l ( f )· GSTF l,l T −1 ( f )}

wherein:
g pre,l T (t)=the pre-emphasized gradient for direction l and Temperature T,
=Fourier transform,
G nom,l (f)=nominal uncorrected gradient at frequency f, direction l (for a reference temperature state, and
GSTF l,l T −1 (f)=gradient system transfer function at the frequency f and the direction l (for a specific temperature state T).

17. The method of claim 9 , further comprising:
reconstructing an image of the patient, wherein the reconstructed image comprises a reduced number of artifacts in comparison to a MR image acquisition process without use of the pre-emphasized gradient in the imaging.

18. A magnetic resonance (MR) device comprising:
a plurality of gradient coils having a first gradient coil for an x-axis, a second gradient coil for a y-axis, and a third gradient coil for a z-axis of the MR device;
at least one temperature sensor for each gradient coil of the plurality of gradient coils, the at least one temperature sensor configured to monitor a temperature of the respective gradient coil;
at least one processor configured to set at least one gradient coil to a target temperature, measure a behavior of the MR device for the at least one gradient coil at different frequencies generated by varying current through the at least one gradient coil, and develop at least one characterization function for the at least one gradient coil at the target temperature based on the measured behavior; and
a database or non-transitory memory configured to store the at least one characterization function of the at least one gradient coil of the plurality of gradient coils.

Assignees

• Ruyters Gudrun
• Dewdney Andrew
• Stich Manuel
• Koestler Herbert
• Pfaff Christiane
• Wech Tobias
• Campbell Adrienne
• Siemens Healthcare Gmbh
• Univ Wuerzburg J Maximilians
• Us Health

Inventors

• Ruyters Gudrun
• Dewdney Andrew
• Stich Manuel
• Köstler Herbert
• Pfaff Christiane
• Wech Tobias
• Campbell Adrienne

Classifications

• G01R33/3856 Primary

  Means for cooling the gradient coils or thermal shielding of the gradient coils · CPC title

• G01R33/3852

  Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer · CPC title

• G01R33/56518

  due to eddy currents, e.g. caused by switching of the gradient magnetic field · CPC title

• G01R33/56572 Primary

  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 title