Determining a position of a subarea of an object under examination and the structure thereof in a magnetic resonance system

1. A method for determining a location of a subarea of an object under examination in a magnetic resonance system, the subarea being arranged at an edge of a field-of-view of the magnetic resonance system, the method comprising:

determining at least one slice position for an MR image, in which a field at the edge of the MR image fulfills a homogeneity criterion;

acquiring an MR image in the determined at least one slice position, the acquired MR image containing the subarea at the edge of the field-of-view; and

determining the location of the subarea of the object under examination through a location of the subarea in the acquired MR image.

2. The method as claimed in claim 1 , wherein the MR image is acquired in a first slice plane and wherein, to determine the at least one slice position for the MR image in which the field at the edge of the MR image fulfils the homogeneity criterion, a further MR image is acquired in a second slice plane and in the further MR image, at least one slice position for the MR image is determined in which signal values at the edge of the further MR image fulfill a signal value criterion.

3. The method according to claim 2 , wherein the second slice plane is a plane of the object under examination.

4. The method as claimed in claim 1 , wherein, the step of determining the at least one slice position for the MR image in which the field at the edge of the MR image fulfills the homogeneity criterion includes:

acquiring a number of MR images in slice planes parallel to the plane of the MR image; and

determining the at least one slice position for the MR image as a function of slice positions of those of the number of MR images in which signal values at the edge fulfill a signal value criterion.

5. The method as claimed in claim 2 , wherein the signal values at the edge which exceed a threshold value fulfill the signal value criterion.

6. The method as claimed in claim 2 , wherein the signal values at the edge which have a signal value relationship to adjacent signal values fulfill the signal value criterion.

7. The method according to claim 1 , wherein, for determining the at least one slice position for the MR image in which the field at the edge of the MR image fulfils the homogeneity criterion, a field distribution in the field of view including the edge of the field of view is determined.

8. The method as claimed in claim 1 , wherein the subarea of the object under examination includes an anatomical structure of a patient which is arranged at the edge of the field-of-view of the magnetic resonance system.

9. The method as claimed in claim 8 , wherein the anatomical structure includes an arm of the patient.

10. The method as claimed in claim 1 , wherein the magnetic resonance system includes a tunnel-shaped opening to accommodate the object under examination, with the edge of the field-of-view comprising an inner casing area along an inner surface of the tunnel-shaped opening.

11. The method as claimed in claim 10 , wherein the inner casing area has an inner casing thickness of approximately 5 cm.

12. The method as claimed in claim 1 , wherein the MR image is acquired in a transversal plane.

13. The method as claimed in claim 1 , wherein the attenuation correction for a positron emission tomography is determined as a function of the specified location of the subarea of the object under examination.

14. A magnetic resonance system, comprising:

a magnetic resonance system including

a control unit to control a tomograph with a magnet for generating a field in a field-of-view of the magnetic resonance system, and to receive signals detected by the tomograph, and

an evaluation facility to evaluate the received signals and to create MT images, wherein the magnetic resonance system is embodied to

determine at least one slice position for an MR image in which a field at an edge of the MR image fulfills a homogeneity criterion,

acquire an MR image in the at least one slice position determined, the acquired MR image containing a subarea of an object under examination at an edge of a field-of-view of the magnetic resonance system, and

determine a location of the subarea of the object under examination through a location of the subarea in the acquired MR image.

15. The magnetic resonance system as claimed in claim 14 , wherein the magnetic resonance system also includes a positron emission tomograph, wherein the attenuation correction for a positron emission tomography is determined as a function of the specified location of the subarea of the object under examination.

16. A computer program product, capable of being loaded directly into a memory of a programmable control unit of a magnetic resonance system, comprising program code for executing a method, for determining a location of a subarea of an object under examination in the magnetic resonance system, the subarea being arranged at an edge of a field-of-view of the magnetic resonance system, when the program is executed in the programmable control unit of the magnetic resonance system, the method comprising:

determining at least one slice position for an MR image, in which a field at the edge of the MR image fulfills a homogeneity criterion;

acquiring an MR image in the determined at least one slice position, the acquired MR image containing the subarea at the edge of the field-of-view; and determining the location of the subarea of the object under examination through a location of the subarea in the acquired MR image.

17. An electronically-readable data medium including electronically-readable control information stored thereon, which is embodied, when the data medium is used in a control unit of a magnetic resonance system, to execute a method for determining a location of a subarea of an object under examination in the magnetic resonance system, the subarea being arranged at an edge of a field-of-view of the magnetic resonance system, the method comprising:

determining at least one slice position for an MR image, in which a field at the edge of the MR image fulfills a homogeneity criterion;

acquiring an MR image in the determined at least one slice position, the acquired MR image containing the subarea at the edge of the field-of-view; and

determining the location of the subarea of the object under examination through a location of the subarea in the acquired MR image.

18. A non-transitory computer readable medium including program segments for, when executed in a control unit of a magnetic resonance system, causing the control unit to implement a method, for determining a location of a subarea of an object under examination in the magnetic resonance system, the subarea being arranged at an edge of a field-of-view of the magnetic resonance system, when the program is executed in the programmable control unit of the magnetic resonance system, the method comprising:

determining at least one slice position for an MR image, in which a field at the edge of the MR image fulfills a homogeneity criterion;

acquiring an MR image in the determined at least one slice position, the acquired MR image containing the subarea at the edge of the field-of-view; and

determining the location of the subarea of the object under examination through a location of the subarea in the acquired MR image.

19. The method as claimed in claim 4 , wherein the signal values at the edge which exceed a threshold value fulfill the signal value criterion.

20. The method as claimed in claim 4 , wherein the signal values at the edge which have a signal value relationship to adjacent signal values fulfill the signal value criterion.