Method for determining magnetic resonance data
According to an embodiment of a method, a first readout gradient field is determined in such a way that a distortion caused by a non-linearity of the first readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a first location of a field of view of the magnetic resonance facility. Moreover, a second readout gradient field is determined in such a way that a distortion caused by a non-linearity of the second readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a different second location of the field of view. Finally, a multiecho sequence is performed, wherein first magnetic resonance data is captured using the first readout gradient field after a 180° pulse and second magnetic resonance data is captured using the second readout gradient field after a further 180° pulse.
1. A method for determining magnetic resonance data of an examination object in a magnetic resonance facility, comprising:
determining a first readout gradient field in such a way that a distortion caused by a non-linearity of the first readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a first location of a field of view of the magnetic resonance facility;
determining a second readout gradient field in such a way that a distortion caused by a non-linearity of the second readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a second location of the field of view, the second location being different than the first location; and
performing a multiecho sequence, wherein first magnetic resonance data of a first spin echo is captured using the determined first readout gradient field after a 180° pulse and second magnetic resonance data of a second spin echo is captured using the determined second readout gradient field after a further 180° pulse.
2. A method for determining magnetic resonance data of an examination object in a magnetic resonance facility, comprising:
determining a first readout gradient field in such a way that a distortion caused by a non-linearity of the first readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a first location of a field of view of the magnetic resonance facility;
determining a second readout gradient field in such a way that a distortion caused by a non-linearity of the second readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a second location of the field of view, the second location being different than the first location; and
performing a combined spin echo/gradient echo sequence, wherein first magnetic resonance data of a first spin echo is captured using the determined first readout gradient field after a 180° pulse of the spin echo sequence, and second magnetic resonance data is then captured using the determined second readout gradient field.
3. The method of claim 1 , wherein the first location and the second location are arranged in a layer of a magnetic resonance recording, determined on the basis of the captured first and second magnetic resonance data.
4. The method of claim 1 , wherein the first readout gradient field and the second readout gradient field have a common gradient direction, wherein the first location and the second location are arranged at essentially opposite ends of the field of view of the magnetic resonance facility in the gradient direction.
5. The method of claim 1 , wherein the determining of the first readout gradient field involves a calculation of a strength and polarity of the first readout gradient field, and wherein a determining of the second readout gradient field involves a calculation of a strength and polarity of the second readout gradient field.
6. The method of claim 1 , wherein provision is further made for checking whether a gradient moment of the first readout gradient field and of the second readout gradient field for the second spin echo is cancelled, and the method further comprising, if the gradient moment is not cancelled, using an additional gradient field in a readout direction before the second readout gradient field, such that the gradient moment of the first readout gradient field, of the additional gradient field and of the second readout gradient field for the second spin echo, are cancelled.
7. The method of claim 1 , wherein the steps for determining the first and second readout gradient field further comprise:
determining a first relative gradient error at the first location,
determining a B 0 field inhomogeneity at the first location,
determining a second relative gradient error at the second location,
determining a B 0 field inhomogeneity at the second location,
determining a first gradient of the first readout gradient field as a function of the first relative gradient error and the B 0 field inhomogeneity at the first location, and
determining a second gradient of the second readout gradient field as a function of the second relative gradient error and the B 0 field inhomogeneity at the second location.
8. The method of claim 7 , wherein the first gradient G 1 and the second gradient G 2 are determined in accordance with the equations
G 1 =−dB 0( x 1 ,y 1 ,z 1 )/ c 1 ( x 1, y 1 ,z 1 ) and
G 2 =−dB 0( x 2 ,y 2 ,z 2 )/ c 2 ( x 2 ,y 2 ,z 2 )
where dB 0 (x 1 ,y 1 ,z 1 ) is the B 0 field inhomogeneity at the first location x 1 ,y 1 ,z 1 , c 1 is the first relative gradient error at the first location x 1 ,y 1 ,z 1 , dB 0 (x 2 ,y 2 ,z 2 ) is the B 0 field inhomogeneity at the second location x 2 ,y 2 ,z 2 , and c 2 is the second relative gradient error at the second location x 2 ,y 2 ,z 2 .
9. The method of claim 1 , wherein the magnetic resonance facility features a tunnel-shaped opening for accommodating the examination object, wherein a margin of the field of view of the magnetic resonance facility comprises a circumferential region along an inner surface of the tunnel-shaped opening, and wherein the first location and the second location are situated in the margin of the field of view.
10. The method of claim 9 , wherein a part region of the examination object is arranged in the margin of the field of view of the magnetic resonance facility, and wherein the part region comprises an anatomical structure of a patient.
11. The method of claim 10 , wherein the anatomical structure comprises an arm of the patient.
12. The method of claim 9 , wherein the circumferential region includes a thickness of approximately 5 cm.
13. The method of claim 10 , wherein image points of a magnetic resonance recording for the first location are determined as a function of the first magnetic resonance data, and image points of the magnetic resonance recording for the second location are determined as a function of the second magnetic resonance data.
14. The method of claim 13 , wherein the magnetic resonance recording is determined in a transverse plane relative to the examination object.
15. The method of claim 13 , wherein a representation of the part region of the examination object at the first location and the second location is determined as a function of the magnetic resonance recording.
16. The method of claim 15 , wherein an attenuation adjustment for a positron emission tomography recording is determined as a function of the representation of the part region of the examination object.
17. A magnetic resonance facility, comprising:
a basic field magnet;
a gradient field system;
a high-frequency antenna; and
a control device configured to activate the gradient field system and the high-frequency antenna, configured to receive measurement signals picked by the high-frequency antenna, configured to evaluate the measurement signals, and configured to produce magnetic resonance recordings, the control device being further configured
to determine a first readout gradient field in such a way that a distortion caused by a non-linearity of the first readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a first location of a field of view of the magnetic resonance facility,
to determine a second readout gradient field in such a way that a distortion caused by a non-linearity of the second readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a second location of the field of view, the second location being different than the first location, and
to perform a multiecho sequence, wherein first magnetic resonance data is captured using the determined first readout gradient field after a 180° pulse and second magnetic resonance data is captured using the determined second readout gradient field after a further 180° pulse.
18. A magnetic resonance facility, comprising:
a basic field magnet;
a gradient field system;
a high-frequency antenna; and
a control device configured to activate the gradient field system and the high-frequency antenna, configured to receive measurement signals picked by the high-frequency antenna, configured to evaluate the measurement signals, and configured to produce magnetic resonance recordings, the control device being configured
to determine a first readout gradient field in such a way that a distortion caused by a non-linearity of the first readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a first location of a field of view of the magnetic resonance facility,
to determine a second readout gradient field in such a way that a distortion caused by a non-linearity of the second readout gradient field and a distortion caused by a B 0 field inhomogeneity are essentially cancelled at a second location of the field of view, the second location being different than the first location, and
to perform a combined spin echo/gradient echo sequence, wherein first magnetic resonance data of a first spin echo is captured using the determined first readout gradient field after a 180° pulse of the spin echo sequence, and second magnetic resonance data is then captured using the determined second readout gradient field.
19. The magnetic resonance facility as claimed in claim 17 , wherein the magnetic resonance facility further comprises a positron emission tomograph.
20. The magnetic resonance facility as claimed in claim 18 , wherein the magnetic resonance facility further comprises a positron emission tomograph.
21. A non-transitory computer program product, directly loadable into a memory of a programmable control device of a magnetic resonance facility, comprising program segments for executing the method as claimed in claim 1 when the program is executed in a control device of the magnetic resonance facility.
22. A non-transitory electronically readable data medium including electronically readable control information stored thereon and configured as to perform, when executed, the method as claimed in claim 1 when the data medium is used in a control device of a magnetic resonance facility.
23. The method of claim 1 , wherein moreover image points of a magnetic resonance recording for the first location are determined as a function of the first magnetic resonance data, and image points of the magnetic resonance recording for the second location are determined as a function of the second magnetic resonance data.
24. The method of claim 2 , wherein the first location and the second location are arranged in a layer of a magnetic resonance recording, determined on the basis of the captured first and second magnetic resonance data.
25. The method of claim 2 , wherein the first readout gradient field and the second readout gradient field have a common gradient direction, wherein the first location and the second location are arranged at essentially opposite ends of the field of view of the magnetic resonance facility in the gradient direction.
26. The method of claim 2 , wherein the determining of the first readout gradient field involves a calculation of a strength and polarity of the first readout gradient field, and wherein a determining of the second readout gradient field involves a calculation of a strength and polarity of the second readout gradient field.
27. The method of claim 2 , wherein provision is further made for checking whether a gradient moment of the first readout gradient field and of the second readout gradient field for the second spin echo is cancelled, and the method further comprising, if the gradient moment is not cancelled, using an additional gradient field in a readout direction before the second readout gradient field, such that the gradient moment of the first readout gradient field, of the additional gradient field and of the second readout gradient field for the second spin echo, are cancelled.
28. The method of claim 2 , wherein the steps for determining the first and second readout gradient field further comprise:
determining a first relative gradient error at the first location,
determining a B 0 field inhomogeneity at the first location,
determining a second relative gradient error at the second location,
determining a B 0 field inhomogeneity at the second location,
determining a first gradient of the first readout gradient field as a function of the first relative gradient error and the B 0 field inhomogeneity at the first location, and
determining a second gradient of the second readout gradient field as a function of the second relative gradient error and the B 0 field inhomogeneity at the second location.
29. The method of claim 28 , wherein the first gradient G 1 and the second gradient G 2 are determined in accordance with the equations
G 1 =−dB 0( x 1 ,y 1 ,z 1 )/ c 1 ( x 1, y 1 ,z 1 ) and
G 2 =−dB 0( x 2 ,y 2 ,z 2 )/ c 2 ( x 2 ,y 2 ,z 2 ),
where dB 0 (x 1 ,y 1 ,z 1 ) is the B 0 field inhomogeneity at the first location x 1 ,y 1 ,z 1 , c 1 is the first relative gradient error at the first location x 1 ,y 1 ,z 1 dB 0 (x 2 ,y 2 ,z 2 ) is the B 0 field inhomogeneity at the second location x 2 ,y 2 ,z 2 , and c 2 is the second relative gradient error at the second location x 2 ,y 2 ,z 2 .
30. The method of claim 2 , wherein the magnetic resonance facility features a tunnel-shaped opening for accommodating the examination object, wherein a margin of the field of view of the magnetic resonance facility comprises a circumferential region along an inner surface of the tunnel-shaped opening, and wherein the first location and the second location are situated in the margin of the field of view.
31. The method of claim 30 , wherein a part region of the examination object is arranged in the margin of the field of view of the magnetic resonance facility, and wherein the part region comprises an anatomical structure of a patient.
32. The method of claim 31 , wherein the anatomical structure comprises an arm of the patient.
33. The method of claim 30 , wherein the circumferential region includes a thickness of approximately 5 cm.
34. The method of claim 31 , wherein image points of a magnetic resonance recording for the first location are determined as a function of the first magnetic resonance data, and image points of the magnetic resonance recording for the second location are determined as a function of the second magnetic resonance data.
35. The method of claim 34 , wherein the magnetic resonance recording is determined in a transverse plane relative to the examination object.
36. The method of claim 34 , wherein a representation of the part region of the examination object at the first location and the second location is determined as a function of the magnetic resonance recording.
37. The method of claim 36 , wherein an attenuation adjustment for a positron emission tomography recording is determined as a function of the representation of the part region of the examination object.
38. A non-transitory computer program product, directly loadable into a memory of a programmable control device of a magnetic resonance facility, comprising program segments for executing the method as claimed in claim 2 when the program is executed in a control device of the magnetic resonance facility.
39. A non-transitory electronically readable data medium including electronically readable control information stored thereon and configured as to perform, when executed, the method as claimed in claim 2 when the data medium is used in a control device of a magnetic resonance facility.
40. A non-transitory computer readable medium including program segments for, when executed on a computer device, causing the computer device to implement the method of claim 1 .
41. A non-transitory computer readable medium including program segments for, when executed on a computer device, causing the computer device to implement the method of claim 2 .