SPATIOTEMPORAL MAGNETIC FIELD MONITORING WITH HALL EFFECT SENSORS DURING THE MRI SCAN

• US 20180292502A1
• Filed: 04/06/2018
• Published: 10/11/2018
• Est. Priority Date: 04/06/2017
• Status: Active Grant

• Current Assignee: Bilkent University
• Original Assignee: Bilkent University
• Inventors: Atalar, Ergin, Taraghinia, Soheil, Ertan, Niyazi Koray, Tasdelen, Bilal
• Granted Patent: US 10,641,858 B2
• Time in Patent Office: Days
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration
• CPC Class Codes: G01R 33/072 Constructional adaptation of the sensor to specific applications
• CPC Class Codes: G01R 33/3852 Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer
• CPC Class Codes: G01R 33/4625 Processing of acquired signals, e.g. elimination of phase errors, baseline fitting, chemometric analysis
• CPC Class Codes: G01R 33/4633 Sequences for multi-dimensional NMR
• 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

Abstract

An MRI system includes a gantry having a longitudinal axis (herein “z-axis”) and a magnet disposed about the gantry for generating a static magnetic field along the longitudinal axis. Additionally, the system comprises a first gradient magnet for generating a gradient magnetic field along the longitudinal axis; a second gradient magnet for generating a gradient magnetic field along a first transverse direction (herein “x-axis”) orthogonal the longitudinal axis; and a third gradient magnet for generating a gradient magnetic field along a second transverse direction (herein “y-axis”) orthogonal to the longitudinal axis and the first transverse direction. Magnetic sensors are positioned relative to the gantry to measure gradients of transverse components of magnetic field along one or more of the x, y and z axes. A controller receives measurement signals from the sensors and operates on those signals to determine gradients of the gradient magnetic field along the longitudinal axis.

Claims

1. A magnetic resonance imaging (MRI) system, comprising:

a gantry for receiving a subject, said gantry having a longitudinal axis (herein “

z-axis”

);

a magnet disposed about said gantry for generating a static magnetic field along said longitudinal axis of the gantry;

a first gradient magnet for generating a gradient magnetic field along said longitudinal axis;

a second gradient magnet for generating a gradient magnetic field along a first transverse direction (herein “

x-axis”

) orthogonal said longitudinal axis;

a third gradient magnet for generating a gradient magnetic field along a second transverse direction (herein “

y-axis”

) orthogonal to said longitudinal axis and said first transverse direction;

a plurality of magnetic sensors positioned relative to the gantry for measuring gradients of transverse components of magnetic field along one or more of the x, y and z axes, said magnetic sensors generating signals indicative of said measured transverse magnetic field gradients; and

a controller for receiving said signals and operating on said signals to determine gradients of the gradient magnetic field along said longitudinal axis.

2. The MRI system of claim 1, wherein said magnetic sensors comprise Hall effect sensors.

3. The MRI system of claim 1, wherein said controller determines said longitudinal magnetic field gradients for said at least one location by using the following relations:

4. The MRI system of claim 1, wherein said controller receives calibration signals from said plurality of sensors in absence of applied magnetic fields and employs said calibration signals for calibrating said magnetic sensors.

5. The MRI system of claim 1, further comprising a mechanical holder to which said plurality of magnetic sensors can be mounted, said mechanical holder being positioned relative to said gantry and being configured to provide coordinates of each of said plurality of magnetic sensors along x, y, and z-axes.

6. The MRI system of claim 1, further comprising at least one alignment mechanism for aligning at least one of said plurality of magnetic sensors along any of said x and y-axes for measuring magnetic fields along said axes.

7. The MRI system of claim 6, wherein said at least one alignment mechanism comprises a piezoelectric actuator coupled to said at least one of said plurality of magnetic sensors.

8. The MRI system of claim 7, wherein said at least one alignment mechanism operates under control of said controller.

9. The MRI system of claim 8, wherein said controller instructs said alignment mechanism to adjust an orientation of said at least one sensor based on an output voltage signal generated by said least one sensor.

10. The MRI system of claim 9, wherein said alignment mechanism is configured to rotate said sensor in response to a control signal from said controller so as to align said at least one sensor along on of said x and y-axes.

11. A method for measuring a gradient magnetic field in a magnetic resonance system, comprising:

positioning a plurality of magnetic sensors relative to a longitudinal axis (herein “

z-axis”

) of a gantry;

using the plurality of magnetic sensors to collect measurements indicative of;

a measurement of a gradient magnetic field along a first transverse direction (herein “

x-axis”

) orthogonal to the longitudinal axis, and

a measurement of a gradient magnetic field along a second transverse direction (herein “

y-axis”

) orthogonal to the longitudinal axis and the first transverse direction;

determining a measurement of a gradient magnetic field along the z-axis based on the measurement of the gradient magnetic field along the x-axis and the measurement of a gradient magnetic field along the y-axis.

12. The method of claim 11, wherein the magnetic sensors comprise Hall effect sensors.

13. The method of claim 11, wherein the plurality of magnetic sensors is located within a mechanical holder and positioning the plurality of magnetic sensors relative to the z-axis comprises:

aligning the mechanical holder with the z-axis.

14. The method of claim 13, wherein the mechanical holder is aligned using a piezoelectric actuator.

15. The method of claim 14, wherein the piezoelectric actuator aligns the mechanical holder based on signals generated by the plurality of magnetic sensors.

16. A magnetic resonance imaging (MRI) system, comprising:

a plurality of magnetic sensors positioned relative to a longitudinal axis (herein “

z-axis”

) of a gantry, wherein the plurality of magnetic sensors are configured to collect measurements during an MRI scan comprising;

a measurement of a gradient magnetic field along a first transverse direction (herein “

x-axis”

) orthogonal to the longitudinal axis, and

a measurement of a gradient magnetic field along a second transverse direction (herein “

y-axis”

) orthogonal to the longitudinal axis and the first transverse direction; and

one or more computers configured to determine a measurement of a gradient magnetic field along the z-axis based on the measurement of the gradient magnetic field along the x-axis and the measurement of the gradient magnetic field along the y-axis;

17. The MRI system of claim 16, wherein the y-axis is orthogonal the x-axis.

18. The MRI system of claim 16, wherein the one or more computers are further configured to:

estimate a k-space trajectory of the MRI scan based on the measurement of the gradient magnetic field along the x-axis and the measurement of the gradient magnetic field along the y-axis; and

use the k-space trajectory to reconstruct one or more images based on k-space data acquired during the MRI scan.

19. The MRI system of claim 17, wherein the one or more computers are further configured to:

estimate patient motion data based on the measurement of the gradient magnetic field along the x-axis and the measurement of the gradient magnetic field along the y-axis; and

using the patient motion data to perform motion correction on the one or more images.

20. The MRI system of claim 16, wherein the plurality of magnetic sensors are Hall effect sensors.