System and method for image warp correction for magnetic resonance imaging

Patent metadata

Field	Value
Publication number	US-9529068-B2
Application number	US-201514903636-A
Country	US
Kind code	B2
Filing date	Apr 27, 2015
Priority date	Apr 27, 2015
Publication date	Dec 27, 2016
Grant date	Dec 27, 2016

Abstract

A method of correcting warping of an acquired image in an MRI system, caused by non-linearities in gradient field profiles of gradient coils is set forth, comprising a) constructing a computer model representing conducting pathways for each gradient coil in said MRI system; b) calculating a predicted magnetic field at each point in space for each said gradient coil in said model; c) measuring actual magnetic field at each point in space for each said gradient coil in said MRI system; d) verifying accuracy of said model by comparing said predicted magnetic field to said actual magnetic field at each said point in space and in the event said model is not accurate then repeating a)-d), and in the event said model is accurate then; constructing a distortion map for mapping coordinates in real space to coordinates in warped space of said acquired image based on deviations of said predicted magnetic field from linearity; and unwarping said warping of the acquired image using said distortion map.

First claim

We claim:

1. A method of correcting warping of an acquired image in an MRI system, caused by non-linearities in gradient field profiles of gradient coils, comprising:
a) constructing a computer model representing conducting pathways for each gradient coil in said MRI system;
b) calculating a predicted magnetic field at each point in space for each said gradient coil in said model;
c) measuring actual magnetic field at each point in space for each said gradient coil in said MRI system;
d) verifying accuracy of said model by comparing said predicted magnetic field to said actual magnetic field at each said point in space and in the event said model is not accurate then repeating a)-d), and in the event said model is accurate then;
e) constructing a distortion map for mapping coordinates in real space to coordinates in warped space of said acquired image based on deviations of said predicted magnetic field from linearity; and
f) unwarping said warping of the acquired image using said distortion map,
wherein said predicted magnetic field is calculated using one of either Biot-Savart equations or an equivalent thereof,
wherein said distortion map is constructed for mapping each point x,y,z in real space to a point x′,y′,z′ of the image in warped space by obtaining B(x,y,z) values from said Biot-Savart equations or equivalent for each said gradient coil,
wherein values of x′, y′ are computed directly from k-space data using inverse gridding from uniform to non-uniform sample locations, and
wherein said inverse gridding is effected by performing an apodization correction in k-space, followed by an Inverse Fourier Transform and then using convolution interpolation in image space with a Kaiser-Bessel kernel.

2. The method of claim 1 , wherein said measuring is performed using a field measuring device.

3. The method of claim 2 , wherein said field measuring device comprises 3-axis Hall probe.

4. The method of claim 1 , wherein said computer model is an element array model of a gradient coil electromagnet comprising a set of elements joined together to form a spatial representation of a wire pattern for each said gradient coil.

5. The method of claim 1 , wherein said Biot-Savart equations or equivalent comprise:

x
′

=

⁢

B
z
x

⁡

(

x
,
y
,
z

)

G
x

=

f
x

⁡

(

x
,
y
,
z

)

y
′

=

⁢

B
z
y

⁡

(

x
,
y
,
z

)

G
y

=

f
y

⁡

(

x
,
y
,
z

)

z
′

=

⁢

B
z
z

⁡

(

x
,
y
,
z

)

G
z

=

f
z

⁡

(

x
,
y
,
z

)

and wherein f is a function of x, y, z, B x represents a component coaxial with a main static field of the predicted magnetic field produced along the X-axis of said MRI system, B y represents a component coaxial with the main static field of the predicted magnetic field produced along the Y-axis of said MRI system, and B z represents a component coaxial with the main static field of the predicted magnetic field produced along the Z-axis of said MRI system.

6. The method of claim 1 , wherein said unwarping is performed in image space using one of either nearest neighbor, linear, or cubic interpolation.

7. The method of claim 1 , wherein the size of the Fourier Transform

Assignees

• Panther Alexander Gyles
• Harris Chad Tyler
• Beatty Phillip J
• Synaptive Medical Barbados Inc

Inventors

• Panther Alexander Gyles
• Harris Chad Tyler
• Beatty Phillip J

Classifications

• G01R33/4818 Primary

  MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space · 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

• G01R33/385

  using gradient magnetic field coils · CPC title

• G01R33/4822

  in three dimensions · CPC title