METHOD AND MAGNETIC RESONANCE SYSTEM FOR IMAGING A PARTIAL REGION OF AN EXAMINATION SUBJECT

• US 20130057282A1
• Filed: 09/07/2012
• Published: 03/07/2013
• Est. Priority Date: 09/07/2011
• Status: Active Grant

• Current Assignee: Siemens Healthineers AG (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Blumhagen, Jan Ole, Fenchel, Matthias, Ladebeck, Ralf
• Granted Patent: US 9,753,113 B2
• Time in Patent Office: Days
• US Class Current: 324/309
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/481 MR combined with positron emission tomography [PET] or single photon emission computed tomography [SPECT]
• CPC Class Codes: G01R 33/56563 caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 G01R33/56509, G01R33/56518, G01R33/56536 take precedence
• 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

In a method and magnetic resonance (MR) apparatus to image a partial region of an examination subject by means of a multislice measurement, which partial region includes at least two measurement slices, and is located at least in part at the edge of a field of view of the magnetic resonance apparatus, for each voxel to be optimized that is located at the edge of the field of view, a gradient field is configured for each measurement slice of the partial region that is to be measured and is used to acquire magnetic resonance data in the multislice measurement. The gradient field is configured so as to cause a nonlinearity of the gradient field and a B₀ field inhomogeneity to cancel at each of the aforementioned voxel to be optimized at the partial region at the edge of the field of view. An image of the partial region of the examination subject is determined from the magnetic resonance data acquired in this manner.

Claims

1. A method to image a partial region of an examination subject in a magnetic resonance system across at least two measurement slices, comprising:

positioning an examination subject in a magnetic resonance data acquisition unit, having a field of view, with a partial region of the examination subject, of which a magnetic resonance image is to be obtained, being located at least in part at an edge of said field of view;

configuring gradients of gradient fields to be generated by a gradient coil system of the data acquisition unit to cause each voxel in said image, that is located at said edge of said field of view, to be optimized in each of said measurement slices of said partial region, and determining said gradients such that a distortion caused by a non-linearity of said gradient field, and a distortion caused by a basic magnetic field inhomogeneity of a basic magnetic field generated in said magnetic resonance data acquisition unit, cancel at each of said voxels to be optimized at said edge of said field of view;

operating said data acquisition unit to acquire magnetic resonance data of said partial region in a multi-slice measurement using said gradients configured for each voxel to be optimized; and

reconstructing an image of said partial region from said magnetic resonance data.

2. A method as claimed in claim 1 comprising operating said magnetic resonance data acquisition unit with the respective gradients configured for the respective gradient fields being used as at least one of a readout gradient field and a slice selection gradient field.

3. A method as claimed in claim 1 comprising configuring each gradient by:

determining a relative gradient error at the respective voxel at the edge of the field of view;

determining said basic magnetic field inhomogeneity at the respective voxel at the edge of the field of view; and

determining the configured gradient dependent on the relative gradient error and the basic magnetic field inhomogeneity for the respective voxel.

4. A method as claimed in claim 3 comprising configuring each gradient G of each gradient field according to:

G=−

dB₀(Δ

x,Δ

y,Δ

z)/c(Δ

x,Δ

y,Δ

z)

wherein dB₀ is the basic magnetic field inhomogeneity at the respective voxel (Δ

x,Δ

y,Δ

z) at said edge of said field of view, and wherein c is the relative gradient error at the respective voxel (Δ

x,Δ

y,Δ

z) at the edge of the field of view.

5. A method as claimed in claim 1 comprising selecting said partial region of said examination subject to comprise an anatomical structure of a patient that is located at said edge of said field of view of said magnetic resonance data acquisition unit.

6. A method as claimed in claim 5 comprising selecting said partial region to encompass an arm of a human as said examination subject.

7. A method as claimed in claim 1 wherein said data acquisition unit comprises a tunnel-shaped opening in which said examination subject is located, and wherein said edge of said field of view comprises a sleeve proceeding along an inner surface of said tunnel-shaped opening.

8. A method as claimed in claim 7 wherein said sleeve has a sleeve thickness of approximately 5 cm.

9. A method as claimed in claim 1 comprising operating said magnetic resonance data acquisition unit to acquire said magnetic resonance data in a transverse plane with respect to the examination subject.

10. A method as claimed in claim 1 comprising, in a processor, determining an attenuation correction for acquisition of positron emission tomography data, dependent on said image of said partial region.

11. A magnetic resonance apparatus comprising:

a magnetic resonance data acquisition unit having a field of view, a gradient coil system that generates respective gradient fields, each exhibiting a gradient, and a basic field magnet that generates a basic magnetic field;

said magnetic resonance data acquisition unit having a patient opening therein configured to receive an examination subject in the magnetic resonance data acquisition unit, with a partial region of the examination subject, of which a magnetic resonance image is to be obtained, being located at least in part at an edge of said field of view;

a processor configured to configure gradients of gradient fields to be generated by the gradient coil system of the data acquisition unit to cause each voxel in said image, that is located at said edge of said field of view, to be optimized in each of said measurement slices of said partial region, and determining said gradients such that a distortion caused by a non-linearity of said gradient field, and a distortion caused by a basic magnetic field inhomogeneity of a basic magnetic field generated in said magnetic resonance data acquisition unit, cancel at each of said voxels to be optimized at said edge of said field of view;

a control unit configured to operate said data acquisition unit to acquire magnetic resonance data of said partial region in a multi-slice measurement using said gradients configured for each voxel to be optimized; and

an image computer configured to reconstruct an image of said partial region from said magnetic resonance data.

12. A magnetic resonance system as claimed in claim 11 comprising a positron emission tomography data acquisition unit, and wherein said processor is configured to determine positron emission tomography data acquisition unit parameters for operating said positron emission tomography data acquisition unit, dependent on said image of said partial region.

13. A non-transitory, computer-readable data storage medium encoded with programming instructions, said data storage medium being loaded into a computerized control and evaluation unit of a magnetic resonance apparatus, said magnetic resonance apparatus comprising a field of view, a gradient coil system that generates respective gradient fields, each exhibiting a gradient, and a basic field magnet that generates a basic magnetic field, and an opening configured to receive an examination subject in the magnetic resonance data acquisition unit with a partial region of the examination subject, of which a magnetic resonance image is to be obtained, being located at least in part at an edge of said field of view;

said programming instructions causing said control and evaluation system to;

configure gradients of gradient fields to be generated by a gradient coil system of the data acquisition unit to cause each voxel in said image, that is located at said edge of said field of view, to be optimized in each of said measurement slices of said partial region, and determining said gradients such that a distortion caused by a non-linearity of said gradient field, and a distortion caused by a basic magnetic field inhomogeneity of a basic magnetic field generated in said magnetic resonance data acquisition unit, cancel at each of said voxels to be optimized at said edge of said field of view;

operate said data acquisition unit to acquire magnetic resonance data of said partial region in a multi-slice measurement using said gradients configured for each voxel to be optimized; and

reconstruct an image of said partial region from said magnetic resonance data.

14. A non-transitory, computer-readable data storage medium as claimed in claim 13 wherein said programming instructions cause said control and evaluation system to determine positron emission tomography data acquisition parameters dependent on said image of said partial region, and to operate a positron emission tomography data acquisition unit with said parameters to acquire positron emission tomography data from said partial region.