Reducing artifacts in magnetic resonance images acquired using propeller echo planar imaging

Patent metadata

Field	Value
Publication number	US-9612307-B2
Application number	US-201214113044-A
Country	US
Kind code	B2
Filing date	Apr 23, 2012
Priority date	Apr 21, 2011
Publication date	Apr 4, 2017
Grant date	Apr 4, 2017

Abstract

In PROPELLER utilizing EPI k-space sampling, phase errors arising primarily from eddy currents can considerably degrade image quality. The phase errors include spatially constant phase errors, spatially linear phase errors, and oblique phase errors. Methods to measure and correct for these phase errors are disclosed. Two or three reference scans are acquired, each reference scan being mutually orthogonal along the orthogonal physical gradient axes in a MRI system. A spatially constant phase error and a spatially linear phase error are determined from each of the reference scans for each relevant physical gradient axis. These phase errors can be used to predict the constant, linear, and oblique phase errors in each blade of an EPI PROPELLER k-space data set. With the known phase errors for each blade, constant, linear, and/or oblique phase correction is applied prior to or during PROPELLER image reconstruction, producing an image with substantially reduced artifacts.

First claim

What is claimed:

1. A method comprising:
acquiring a first reference scan of an object in a magnetic resonance imaging system, wherein acquiring the first reference scan comprises applying a first reference readout gradient along a first axis;
based on the first reference scan, determining a constant phase error c x associated with the first axis and a linear phase error l x along the first axis;
acquiring a second reference scan of the object, wherein acquiring the second reference scan comprises applying a second reference readout gradient along a second axis, the second axis being orthogonal to the first axis;
based on the second reference scan, determining a constant phase error c y associated with the second axis and a linear phase error l y along the second axis;
acquiring a third reference scan of the object, wherein acquiring the third reference scan comprises applying a third reference readout gradient along a third axis, the third axis being orthogonal to the first axis and the second axis;
based on the third reference scan, determining a constant phase error c z associated with the third axis and a linear phase error l z along the third axis;
acquiring a plurality of intersecting blades around a center of k-space, the plurality of intersecting blades being in an imaging plane of k-space, wherein:
each of the plurality of intersecting blades is offset from the first axis by a respective blade angle θ, and
the imaging plane is defined by a rotation matrix A given by:

A
=

[

a
0

a
1

a
2

a
3

a
4

a
5

a
6

a
7

a
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;

for each of the plurality of intersecting blades, determining a constant phase error c θ , a linear phase error l θ , and an oblique phase error o θ , wherein:
the constant phase error c θ is given by:
c θ =( a 0 cosθ+ a 1 sinθ) c x +( a 3 cosθ+ a 4 sinθ) c y +( a 6 cosθ+ a 7 sinθ) c z ;

the linear phase error l θ is given by:
l θ =( a 0 cosθ+ a 1 sinθ) 2 l x +( a 3 cosθ+ a 4 sinθ) 2 l y +( a 6 cosθ+ a 7 sinθ) 2 l z ;

the oblique phase error is given by:

o
θ

=

F
⁢

⁢
O
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⁢

V
pe

F
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⁢
O
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⁢

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ro

·

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ro

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pe

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sin
⁢

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2
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(

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2

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a
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2

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l
x

+

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Assignees

• Zhou Xiaohong Joe
• Univ Illinois

Inventors

• Zhou Xiaohong Joe

Classifications

• G01R33/5616

  using gradient refocusing, e.g. EPI · CPC title

• G01R33/565 Primary

  Correction of image distortions, e.g. due to magnetic field inhomogeneities · CPC title

• G01R33/4824 Primary

  using a non-Cartesian trajectory · CPC title

• G01R33/56518

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

• G01R33/56554

  caused by acquiring plural, differently encoded echo signals after one RF excitation, e.g. correction for readout gradients of alternating polarity in EPI · CPC title